13 Working with Oracle Object Types

Retrieving STRUCT Objects and Attributes

This section discusses how to retrieve and manipulate Oracle objects and their attributes, using either Oracle-specific features or JDBC 2.0 standard features.

Retrieving an Oracle Object as a java.sql.Struct Object

Alternatively, in the preceding example, you can use standard JDBC functionality, such as getObject, to retrieve an Oracle object from the database as an instance of java.sql.Struct. The getObject method returns a java.lang.Object, so, you must cast the output of the method to Struct. For example:

ResultSet rs= stmt.executeQuery("SELECT * FROM struct_table");
java.sql.Struct jdbcStruct = (java.sql.Struct)rs.getObject(1);

Retrieving Attributes as oracle.sql Types

If you want to retrieve Oracle object attributes from a STRUCT or Struct instance as oracle.sql types, then use the getOracleAttributes method of the oracle.sql.STRUCT class, as follows:

oracle.sql.Datum[] attrs = oracleSTRUCT.getOracleAttributes();

or:

oracle.sql.Datum[] attrs = ((oracle.sql.STRUCT)jdbcStruct).getOracleAttributes();

Retrieving Attributes as Standard Java Types

If you want to retrieve Oracle object attributes as standard Java types from a STRUCT or Struct instance, use the standard getAttributes method:

Object[] attrs = jdbcStruct.getAttributes();

Creating STRUCT Objects

For information about creating STRUCT objects, refer to "Overview of Class oracle.sql.STRUCT".

Binding STRUCT Objects into Statements

To bind an oracle.sql.STRUCT object to a prepared statement or callable statement, you can either use the standard setObject method (specifying the type code), or cast the statement object to an Oracle statement type and use the Oracle extension setOracleObject method. For example:

PreparedStatement ps= conn.prepareStatement("text_of_prepared_statement");
Struct mySTRUCT = conn.createStruct (...);
ps.setObject(1, mySTRUCT, Types.STRUCT);

or:

PreparedStatement ps= conn.prepareStatement("text_of_prepared_statement");
Struct mySTRUCT = conn.createStruct (...);
((OraclePreparedStatement)ps).setOracleObject(1, mySTRUCT);

STRUCT Automatic Attribute Buffering

Oracle JDBC driver furnishes public methods to enable and disable buffering of STRUCT attributes.

The following methods are included with the oracle.sql.STRUCT class:

• public void setAutoBuffering(boolean enable)

• public boolean getAutoBuffering()

The setAutoBuffering(boolean) method enables or disables auto-buffering. The getAutoBuffering method returns the current auto-buffering mode. By default, auto-buffering is disabled.

It is advisable to enable auto-buffering in a JDBC application when the STRUCT attributes are accessed more than once by the getAttributes and getArray methods, presuming the ARRAY data is able to fit into the Java Virtual Machine (JVM) memory without overflow.

When you enable auto-buffering, the oracle.sql.STRUCT object keeps a local copy of all the converted attributes. This data is retained so that subsequent access of this information does not require going through the data format conversion process.

Relative Advantages of OracleData versus SQLData

In deciding which of the two interface implementations to use, you need to consider the advantages of OracleData and SQLData.

The SQLData interface is for mapping SQL objects only. The OracleData interface is more flexible, enabling you to map SQL objects as well as any other SQL type for which you want to customize processing. You can create an OracleData implementation from any data type found in Oracle Database. This could be useful, for example, for serializing RAW data in Java.

Advantages of the OracleData Interface

The advantages of the OracleData interface are:

• It does not require an entry in the type map for the Oracle object.

• It has awareness of Oracle extensions.

• You can construct an OracleData from an oracle.sql.STRUCT. This is more efficient because it avoids unnecessary conversions to native Java types.

• You can obtain the corresponding JDBC object from OracleData, using the toJDBCObject method.

Advantages of SQLData

SQLData is a JDBC standard that makes your code portable.

Understanding Type Maps for SQLData Implementations

If you use the SQLData interface in a custom object class, then you must create type map entries that specify the custom object class to use in mapping the Oracle object type to Java. You can either use the default type map of the connection object or a type map that you specify when you retrieve the data from the result set. The getObject method of the ResultSet interface has a signature that lets you specify a type map. You can use either of the following:

rs.getObject(int columnIndex);

rs.getObject(int columnIndex, Map map);

When using a SQLData implementation, if you do not include a type map entry, then the object maps to the oracle.jdbc.OracleStruct interface by default. OracleData implementations, by contrast, have their own mapping functionality so that a type map entry is not required. When using an OracleData implementation, use the Oracle getObject(int columnindex, OracleDataFactory factory)method.

The type map relates a Java class to the SQL type name of an Oracle object. This one-to-one mapping is stored in a hash table as a keyword-value pair. When you read data from an Oracle object, the JDBC driver considers the type map to determine which Java class to use to materialize the data from the Oracle object type. When you write data to an Oracle object, the JDBC driver gets the SQL type name from the Java class by calling the getSQLTypeName method of the SQLData interface. The actual conversion between SQL and Java is performed by the driver.

The attributes of the Java class that corresponds to an Oracle object can use either Java native types or Oracle native types to store attributes.

Creating Type Map and Defining Mappings for a SQLData Implementation

When using a SQLData implementation, the JDBC applications programmer is responsible for providing a type map, which must be an instance of a class that implements the standard java.util.Map interface.

You have the option of creating your own class to accomplish this, but the standard java.util.Hashtable class meets the requirement.

Hashtable and other classes used for type maps implement a put method that takes keyword-value pairs as input, where each key is a fully qualified SQL type name and the corresponding value is an instance of a specified Java class.

A type map is associated with a connection instance. The standard java.sql.Connection interface and the Oracle-specific oracle.jdbc.OracleConnection interface include a getTypeMap method. Both return a Map object.

This section covers the following topics:

• Adding Entries to an Existing Type Map

• Creating a New Type Map

• Materializing Object Types not Specified in the Type Map

Reading and Writing Data with a SQLData Implementation

This section describes how to read data from an Oracle object or write data to an Oracle object if your corresponding Java class implements SQLData.

Reading SQLData Objects from a Result Set

The following text summarizes the steps to read data from an Oracle object into your Java application when you choose the SQLData implementation for your custom object class.

These steps assume you have already defined the Oracle object type, created the corresponding custom object class, updated the type map to define the mapping between the Oracle object and the Java class, and defined a statement object stmt.

1. Query the database to read the Oracle object into a JDBC result set.

   ResultSet rs = stmt.executeQuery("SELECT emp_col FROM personnel");
   

   The PERSONNEL table contains one column, EMP_COL, of SQL type EMP_OBJECT. This SQL type is defined in the type map to map to the Java class Employee.

2. Use the getObject method of Oracle result set to populate an instance of your custom object class with data from one row of the result set. The getObject method returns the user-defined SQLData object because the type map contains an entry for Employee.

   if (rs.next())
      Employee emp = (Employee)rs.getObject(1);
   

   Note that if the type map did not have an entry for the object, then the getObject method will return an oracle.jdbc.OracleStruct object. Cast the output to type OracleStruct because the getObject method signature returns the generic java.lang.Object type.

   if (rs.next())
      OracleStruct empstruct = (OracleStruct)rs.getObject(1);
   

   The getObject method calls readSQL, which, in turn, calls readXXX from the SQLData interface.

   Note:

   If you want to avoid using the defined type map, then use the getSTRUCT method. This method always returns a STRUCT object, even if there is a mapping entry in the type map.

3. If you have get methods in your custom object class, then use them to read data from your object attributes. For example, if EMPLOYEE has the attributes EmpName of type CHAR and EmpNum of type NUMBER, then provide a getEmpName method that returns a Java String and a getEmpNum method that returns an int value. Then call them in your Java application, as follows:

   String empname = emp.getEmpName();
   int empnumber = emp.getEmpNum();
    
   

Retrieving SQLData Objects from a Callable Statement OUT Parameter

Consider you have a CallableStatement instance, cs, that calls a PL/SQL function GETEMPLOYEE. The program passes an employee number to the function. The function returns the corresponding Employee object. To retrieve this object you do the following:

1. Prepare a CallableStatement to call the GETEMPLOYEE function, as follows:

   CallableStatement ocs = conn.prepareCall("{ ? = call GETEMPLOYEE(?) }");
   

2. Declare the empnumber as the input parameter to GETEMPLOYEE. Register the SQLData object as the OUT parameter, with the type code OracleTypes.STRUCT. Then, run the statement. This can be done as follows:

   cs.setInt(2, empnumber); 
   cs.registerOutParameter(1, OracleTypes.STRUCT, "EMP_OBJECT"); 
   cs.execute(); 
   

3. Use the getObject method to retrieve the employee object.

   Employee emp = (Employee)cs.getObject(1);
   

   If there is no type map entry, then the getObject method will return a java.sql.Struct object.

   Struct emp = cs.getObject(1);
   

Passing SQLData Objects to a Callable Statement as an IN Parameter

Suppose you have a PL/SQL function addEmployee(?) that takes an Employee object as an IN parameter and adds it to the PERSONNEL table. In this example, emp is a valid Employee object.

1. Prepare an CallableStatement to call the addEmployee(?) function.

   CallableStatement cs = 
     conn.prepareCall("{ call addEmployee(?) }");
   

2. Use setObject to pass the emp object as an IN parameter to the callable statement. Then, call the statement.

   cs.setObject(1, emp); 
   cs.execute();
   

Writing Data to an Oracle Object Using a SQLData Implementation

The following text describes the steps in writing data to an Oracle object from your Java application when you choose the SQLData implementation for your custom object class.

This description assumes you have already defined the Oracle object type, created the corresponding Java class, and updated the type map to define the mapping between the Oracle object and the Java class.

1. If you have set methods in your custom object class, then use them to write data from Java variables in your application to attributes of your Java data type object.

   emp.setEmpName(empname);
   emp.setEmpNum(empnumber);
   

2. Prepare a statement that updates an Oracle object in a row of a database table, as appropriate, using the data provided in your Java data type object.

   PreparedStatement pstmt = conn.prepareStatement
                             ("INSERT INTO PERSONNEL VALUES (?)");
   

3. Use the setObject method of the prepared statement to bind your Java data type object to the prepared statement.

   pstmt.setObject(1, emp);
   

4. Run the statement, which updates the database.

   pstmt.executeUpdate();
   

Understanding the OracleData Interface

You can create a custom object class that implements the oracle.jdbc.OracleData and the oracle.jdbc.OracleDataFactory interfaces to make an Oracle object and its attribute data available to Java applications. The OracleData and OracleDataFactory interfaces are Oracle-specific and are not a part of the JDBC standard.

Understanding the OracleData Interface Features

The OracleData interface has the following advantages:

• It supports Oracle extensions to the standard JDBC types.

• It does not require a type map to specify the names of the Java custom classes you want to create.

• It provides better performance. OracleData works directly with Datum types, the internal format the driver uses to hold Oracle objects.

The OracleData and the OracleDataFactory interfaces perform the following:

• The toJDBCObject method of the OracleData class transforms the data into an oracle.jdbc.* representation.

• OracleDataFactory specifies a create method equivalent to a constructor for the custom object class. It creates and returns an OracleData instance. The JDBC driver uses the create method to return an instance of the custom object class to your Java application or applet. It takes as input a java.lang.Object object and an integer indicating the corresponding SQL type code as specified in the OracleTypes class.

OracleData and OracleDataFactory have the following definitions:

package oracle.jdbc;
import java.sql.Connection;
import java.sql.SQLException;
public interface OracleData 
{
   public Object toJDBCObject(Connection conn) throws SQLException;
}

package oracle.jdbc;
import java.sql.SQLException;
public interface OracleDataFactory 
{
    public OracleData create(Object jdbcValue, int sqlType) throws SQLException;
  
}

Where conn represents the Connection object, jdbcValue represents an object of type java.lang.object that is to be used to initialize the Object being created, and sqlType represents the SQL type of the specified Datum object.

Retrieving and Inserting Object Data

The JDBC drivers provide the following methods to retrieve and insert object data as instances of OracleData.

You can retrieve the object data in one of the following ways:

• Use the following getObject method of the Oracle-specific OracleResultSet interface:

  ors.getObject(int col_index, OracleDataFactory factory
  );
  

  This method takes as input the column index of the data in your result set and an OracleDataFactory instance. For example, you can implement a getOracleDataFactory method in your custom object class to produce the OracleDataFactory instance to input to the getObject method. The type map is not required when using Java classes that implement OracleData.

• Use the standard getObject(index, map) method specified by the ResultSet interface to retrieve data as instances of OracleData. In this case, you must have an entry in the type map that identifies the factory class to be used for the given object type and its corresponding SQL type name.

You can insert object data in one of the following ways:

• Use the following setObject method of the Oracle-specific OraclePreparedStatement class:

  setObject(int bind_index, Object custom_object);
  

  This method takes as input the parameter index of the bind variable and an instance of OracleData as the name of the object containing the variable.

• Use the standard setObject method specified by the PreparedStatement interface. You can also use this method, in its different forms, to insert OracleData instances without requiring a type map.

The following sections describe the getObject and setObject methods.

To continue the example of an Oracle object EMPLOYEE, you might have something like the following in your Java application:

OracleData obj = ors.getObject(1, Employee.getOracleDataFactory());

In this example, ors is an instance of the OracleResultSet interface, getObject is a method in the OracleResultSet interface used to retrieve an OracleData object, and the EMPLOYEE is in column 1 of the result set. The static Employee.getOracleDataFactory method will return an OracleDataFactory to the JDBC driver. The JDBC driver will call create() from this object, returning to your Java application an instance of the Employee class populated with data from the result set.

Reading and Writing Data with an OracleData Implementation

This section describes how to read data from an Oracle object or write data to an Oracle object if your corresponding Java class implements OracleData.

Reading Data from an Oracle Object Using an OracleData Implementation

The following text summarizes the steps in reading data from an Oracle object into your Java application. These steps apply whether you implement OracleData manually or use JPublisher to produce your custom object classes.

These steps assume you have already defined the Oracle object type, created the corresponding custom object class or had JPublisher create it for you, and defined a statement object stmt.

1. Query the database to read the Oracle object into a result set, casting it to an Oracle result set.

   OracleResultSet ors = (OracleResultSet)stmt.executeQuery
                         ("SELECT Emp_col FROM PERSONNEL");
   

   Where PERSONNEL is a one-column table. The column name is Emp_col of type Employee_object.

2. Use the getObject method of Oracle result set to populate an instance of your custom object class with data from one row of the result set. The getObject method returns a java.lang.Object object, which you can cast to your specific custom object class.

   if (ors.next())
      Employee emp = (Employee)ors.getObject(1, Employee.getOracleDataFactory());
   

   or:

   if (ors.next())
      Object obj = ors.getObject(1, Employee.getOracleDataFactory());
   

   This example assumes that Employee is the name of your custom object class and ors is the name of your OracleResultSet instance.

   For example, if the SQL type name for your object is EMPLOYEE, then the corresponding Java class is Employee, which will implement OracleData. The corresponding Factory class is EmployeeFactory, which will implement OracleDataFactory.

   Use this statement to declare the EmployeeFactory entry for your type map:

   map.put ("EMPLOYEE", Class.forName ("EmployeeFactory")); 
   

   Then use the form of getObject where you specify the map object:

   Employee emp = (Employee) rs.getObject (1, map);
   

   If the default type map of the connection already has an entry that identifies the factory class to be used for the given object type and its corresponding SQL type name, then you can use this form of getObject:

   Employee emp = (Employee) rs.getObject (1); 
   

3. If you have get methods in your custom object class, then use them to read data from your object attributes into Java variables in your application. For example, if EMPLOYEE has EmpName of type CHAR and EmpNum of type NUMBER, provide a getEmpName method that returns a Java String and a getEmpNum method that returns an integer. Then call them in your Java application as follows:

   String empname = emp.getEmpName();
   int empnumber = emp.getEmpNum();
   

Writing Data to an Oracle Object Using an OracleData Implementation

The following text summarizes the steps in writing data to an Oracle object from your Java application. These steps apply whether you implement OracleData manually or use JPublisher to produce your custom object classes.

These steps assume you have already defined the Oracle object type and created the corresponding custom object class.

1. If you have set methods in your custom object class, then use them to write data from Java variables in your application to attributes of your Java data type object.

   emp.setEmpName(empname);
   emp.setEmpNum(empnumber);
   

2. Write an Oracle prepared statement that updates an Oracle object in a row of a database table, as appropriate, using the data provided in your Java data type object.

   OraclePreparedStatement opstmt = conn.prepareStatement
      ("UPDATE PERSONNEL SET Employee = ? WHERE Employee.EmpNum = 28959);
   

   This assumes conn is your Connection object.

3. Use the setObject method of the OraclePreparedStatement interface to bind your Java data type object to the prepared statement.

   opstmt.setObject(1,emp);
   

   The setObject method calls the toJDBCObject method of the custom object class instance to retrieve an oracle.jdbc.OracleStruct object that can be written to the database.

   Note:

   You can use your Java data type objects as either IN or OUT bind variables.

Additional Uses for OracleData

The OracleData interface offers far more flexibility than the SQLData interface. The SQLData interface is designed to let you customize the mapping of only Oracle object types to Java types of your choice. Implementing the SQLData interface lets the JDBC driver populate fields of a custom Java class instance from the original SQL object data, and the reverse, after performing the appropriate conversions between Java and SQL types.

The OracleData interface goes beyond supporting the customization of Oracle object types to Java types. It lets you provide a mapping between Java object types and any SQL type supported by the oracle.sql package.

You may find it useful to provide custom Java classes to wrap oracle.sql.* types and then implement customized conversions or functionality as well. The following are some possible scenarios:

• Performing encryption and decryption or validation of data

• Performing logging of values that have been read or are being written

• Parsing character columns, such as character fields containing URL information, into smaller components

• Mapping character strings into numeric constants

• Making data into more desirable Java formats, such as mapping a DATE field to java.util.Date format

• Customizing data representation, for example, data in a table column is in feet but you want it represented in meters after it is selected

• Serializing and deserializing Java objects

For example, use OracleData to store instances of Java objects that do not correspond to a particular SQL object type in the database in columns of SQL type RAW. The create method in OracleDataFactory would have to implement a conversion from an object of type oracle.sql.RAW to the desired Java object. The toJDBCObject method in OracleData would have to implement a conversion from the Java object to an oracle.sql.RAW object. You can also achieve this using Java serialization.

Upon retrieval, the JDBC driver transparently retrieves the raw bytes of data in the form of an oracle.sql.RAW and calls the create method of OracleDataFactory to convert the oracle.sql.RAW object to the desired Java class.

When you insert the Java object into the database, you can simply bind it to a column of type RAW to store it. The driver transparently calls the OracleData.toJDBCObject method to convert the Java object to an oracle.sql.RAW object. This object is then stored in a column of type RAW in the database.

Support for the OracleData interfaces is also highly efficient because the conversions are designed to work using oracle.sql.* formats, which happen to be the internal formats used by the JDBC drivers. Moreover, the type map, which is necessary for the SQLData interface, is not required when using Java classes that implement OracleData.

Creating Subtypes

Create custom object classes if you want to have Java classes that explicitly correspond to the Oracle object types. If you have a hierarchy of object types, you may want a corresponding hierarchy of Java classes.

The most common way to create a database subtype in JDBC is to run a SQL CREATE TYPE command using the execute method of the java.sql.Statement interface. For example, you want to create a type inheritance hierarchy as depicted in Figure 13-1:

Figure 13-1 Type Inheritance Hierarchy

Description of "Figure 13-1 Type Inheritance Hierarchy"

The JDBC code for this can be as follows:

Statement s = conn.createStatement();
s.execute ("CREATE TYPE Person_T (SSN NUMBER, name VARCHAR2(30),
  address VARCHAR2(255))");
s.execute ("CREATE TYPE Student_T UNDER Person_t (deptid NUMBER,
  major VARCHAR2(100))");
s.execute ("CREATE TYPE PartTimeStudent_t UNDER Student_t (numHours NUMBER)");

In the following code, the foo member procedure in type ST is overloaded and the member procedure print overwrites the copy it inherits from type T.

CREATE TYPE T AS OBJECT (..., 
  MEMBER PROCEDURE foo(x NUMBER), 
  MEMBER PROCEDURE Print(), 
  ... 
  NOT FINAL; 

CREATE TYPE ST UNDER T (..., 
  MEMBER PROCEDURE foo(x DATE),         <-- overload "foo" 
  OVERRIDING MEMBER PROCEDURE Print(),   <-- override "print" 
  STATIC FUNCTION bar(...) ... 
  ... 
  );

Once the subtypes have been created, they can be used as both columns of a base table as well as attributes of a object type.

Implementing Customized Classes for Subtypes

In most cases, a customized Java class represents a database object type. When you create a customized Java class for a subtype, the Java class can either mirror the database object type hierarchy or not.

You can use either the OracleData or SQLData solution in creating classes to map to the hierarchy of object types.

This section covers the following topics:

• Use of OracleData for Type Inheritance Hierarchy

• Use of SQLData for Type Inheritance Hierarchy

• JPublisher Utility

public static OracleDataFactory getOracleDataFactory() 
  { 
    return _personFactory; 
  } 
 
  public Person () {} 
 
  public Person(NUMBER ssn, CHAR name, CHAR address) 
  { 
    this.ssn = ssn; 
    this.name = name; 
    this.address = address; 
  } 
 
  public Object toJDBCObject(OracleConnection c) throws SQLException 
  { 
    Object [] attributes = { ssn, name, address };
 Struct struct = c.createStruct("HR.PERSON_T", attributes);
    return struct; 
  } 
 
  public OracleData create(Object jdbcValue, int sqlType) throws SQLException 
  { 
    if (d == null) return null; 
    Object [] attributes = ((STRUCT) d).getOracleAttributes(); 
    return new Person((NUMBER) attributes[0], 
                      (CHAR) attributes[1], 
                      (CHAR) attributes[2]); 
  } 
}

class Student extends Person 
{ 
  static final Student _studentFactory = new Student (); 
 
  public NUMBER deptid; 
  public CHAR major; 
 
  public static OracleDataFactory getOracleDataFactory() 
  { 
    return _studentFactory; 
  } 
 
  public Student () {} 
 
  public Student (NUMBER ssn, CHAR name, CHAR address, 
                  NUMBER deptid, CHAR major) 
  { 
    super (ssn, name, address); 
    this.deptid = deptid; 
    this.major = major; 
  } 
 
  public Object toJDBCObject(OracleConnection c) throws SQLException 
  { 
    Object [] attributes = { ssn, name, address, deptid, major };
    Struct struct = c.createStruct("HR.STUDENT_T", attributes);
    return struct; 
  } 
 
  public OracleData create(Object jdbcValue, int sqlType) throws SQLException 
  { 
    if (d == null) return null; 
    Object [] attributes = ((STRUCT) d).getOracleAttributes(); 
    return new Student((NUMBER) attributes[0], 
                       (CHAR) attributes[1], 
                       (CHAR) attributes[2], 
                       (NUMBER) attributes[3], 
                       (CHAR) attributes[4]); 
  } 
}

ResultSet rset = stmt.executeQuery ("select person from tab1"); 
while (rset.next()) 
{ 
  rset.getOracleData(1,Person.getOracleDataFactory());
  ... 
} 

class PersonFactory implements OracleDataFactory 
{ 
  static final PersonFactory _factory = new PersonFactory (); 
 
  public static OracleDataFactory getOracleDataFactory() 
  { 
    return _factory; 
  } 
 
  public OracleData create(Object jdbcValue, int sqlType) throws SQLException 
  { 
    STRUCT s = (STRUCT) jdbcValue; 
    if (s.getSQLTypeName ().equals ("HR.PERSON_T")) 
      return Person.getOracleDataFactory ().create (jdbcValue, sqlType); 
    else if (s.getSQLTypeName ().equals ("HR.STUDENT_T")) 
      return Student.getOracleDataFactory ().create(jdbcValue, sqlType); 
    else if (s.getSQLTypeName ().equals ("HR.PARTTIMESTUDENT_T")) 
      return ParttimeStudent.getOracleDataFactory ().create(jdbcValue, sqlType); 
    else 
      return null; 
  } 
}

CREATE TABLE tabl1 (idx NUMBER, person PERSON_T); 
INSERT INTO tabl1 VALUES (1, PERSON_T (1000, 'HR', '100 Oracle Parkway')); 
INSERT INTO tabl1 VALUES (2, STUDENT_T (1001, 'Peter', '200 Oracle Parkway', 101, 'CS')); 
INSERT INTO tabl1 VALUES (3, PARTTIMESTUDENT_T (1002, 'David', '300 Oracle Parkway', 102, 'EE')); 

import java.sql.*; 

public class Person implements SQLData 
{ 
  private String sql_type; 
  public int ssn; 
  public String name; 
  public String address; 

  public Person () {} 

  public String getSQLTypeName() throws SQLException { return sql_type; } 

  public void readSQL(SQLInput stream, String typeName) throws SQLException 
  { 
    sql_type = typeName; 
    ssn = stream.readInt(); 
    name = stream.readString(); 
    address = stream.readString(); 
  } 

  public void writeSQL(SQLOutput stream) throws SQLException 
  { 
    stream.writeInt (ssn); 
    stream.writeString (name); 
    stream.writeString (address); 
  } 
}

import java.sql.*; 

public class Student extends Person 
{ 
  private String sql_type; 
  public int deptid; 
  public String major; 

  public Student () { super(); } 

  public String getSQLTypeName() throws SQLException { return sql_type; } 

  public void readSQL(SQLInput stream, String typeName) throws SQLException 
  { 
    super.readSQL (stream, typeName);    // read supertype attributes 
    sql_type = typeName;
    deptid = stream.readInt(); 
    major = stream.readString(); 
  } 

  public void writeSQL(SQLOutput stream) throws SQLException 
  { 
    super.writeSQL (stream);        // write supertype
                                         // attributes 
    stream.writeInt (deptid); 
    stream.writeString (major); 
  } 
}

import java.sql.*; 

public class Student implements SQLData 
{ 
  private String sql_type; 

  public int ssn; 
  public String name; 
  public String address; 
  public int deptid; 
  public String major; 

  public Student () {} 

  public String getSQLTypeName() throws SQLException { return sql_type; } 

  public void readSQL(SQLInput stream, String typeName) throws SQLException 
  { 
    sql_type = typeName; 
    ssn = stream.readInt(); 
    name = stream.readString(); 
    address = stream.readString(); 
    deptid = stream.readInt(); 
    major = stream.readString(); 
  } 

  public void writeSQL(SQLOutput stream) throws SQLException 
  { 
    stream.writeInt (ssn); 
    stream.writeString (name); 
    stream.writeString (address); 
    stream.writeInt (deptid); 
    stream.writeString (major); 
  } 
}

Retrieving Subtype Objects

In a typical JDBC application, a subtype object is returned as one of the following:

• A query result

• A PL/SQL OUT parameter

• A type attribute

You can use either the default mapping or the SQLData mapping or the OracleData mapping to retrieve a subtype.

Using Default Mapping

By default, a database object is returned as an instance of the oracle.jdbc.OracleStruct interface. This instance may represent an object of either the declared type or subtype of the declared type. If the OracleStruct interface represents a subtype object in the database, then it contains the attributes of its supertype as well as those defined in the subtype.

Oracle JDBC driver returns database objects in their most specific type. The JDBC application can use the getSQLTypeName method of the OracleStruct interface to determine the SQL type of the STRUCT object. The following code shows this:

// tab1.person column can store PERSON_T, STUDENT_T and PARTIMESTUDENT_T objects 
ResultSet rset = stmt.executeQuery ("select person from tab1"); 
while (rset.next()) 
{ 
  oracle.sql.STRUCT s = (oracle.sql.STRUCT) rset.getObject(1); 
  if (s != null) 
    System.out.println (s.getSQLTypeName());    // print out the type name which 
    // may be HR.PERSON_T, HR.STUDENT_T or HR.PARTTIMESTUDENT_T
}

Using SQLData Mapping

With SQLData mapping, the JDBC driver returns the database object as an instance of the class implementing the SQLData interface.

To use SQLData mapping in retrieving database objects, do the following:

1. Implement the container classes that implement the SQLData interface for the desired object types.

2. Populate the connection type map with entries that specify what custom Java type corresponds to each Oracle object type.

3. Use the getObject method to access the SQL object values.

   The JDBC driver checks the type map for an entry match. If one exists, then the driver returns the database object as an instance of the class implementing the SQLData interface.

The following code shows the whole SQLData customized mapping process:

// The JDBC application developer implements Person.java for PERSON_T, 
// Student.java for STUDENT_T 
// and ParttimeStudent.java for PARTTIMESTUDEN_T. 

Connection conn = ...;  // make a JDBC connection 

// obtains the connection typemap 
java.util.Map map = conn.getTypeMap (); 

// populate the type map 
map.put ("HR.PERSON_T", Class.forName ("Person")); 
map.put ("HR.STUDENT_T", Class.forName ("Student")); 
map.put ("HR.PARTTIMESTUDENT_T", Class.forName ("ParttimeStudent")); 

// tab1.person column can store PERSON_T, STUDENT_T and PARTTIMESTUDENT_T objects 
ResultSet rset = stmt.executeQuery ("select person from tab1"); 
while (rset.next()) 
{ 
  // "s" is instance of Person, Student or ParttimeStudent 
  Object s = rset.getObject(1); 

  if (s != null) 
  { 
    if (s instanceof Person) 
      System.out.println ("This is a Person"); 
    else if (s instanceof Student) 
      System.out.println ("This is a Student"); 
    else if (s instanceof ParttimeStudent) 
      System.out.pritnln ("This is a PartimeStudent"); 
    else 
      System.out.println ("Unknown type"); 
  } 
}

The JDBC drivers check the connection type map for each call to the following:

• getObject method of the java.sql.ResultSet and java.sql.CallableStatement interfaces

• getAttribute method of the java.sql.Struct interface

• getArray method of the java.sql.Array interface

• getValue method of the oracle.sql.REF interface

Using OracleData Mapping

With OracleData mapping, the JDBC driver returns the database object as an instance of the class implementing the OracleData interface.

Oracle JDBC driver needs to be informed of what Java class is mapped to the Oracle object type. The following are the two ways to inform Oracle JDBC drivers:

• The JDBC application uses the getObject(int idx, OracleDataFactory f) method to access database objects. The second parameter of the getObject method specifies an instance of the factory class that produces the customized class. The getObject method is available in the OracleResultSet and OracleCallableStatement interfaces.

• The JDBC application populates the connection type map with entries that specify what custom Java type corresponds to each Oracle object type. The getObject method is used to access the Oracle object values.

The second approach involves the use of the standard getObject method. The following code example demonstrates the first approach:

// tab1.person column can store both PERSON_T and STUDENT_T objects 
ResultSet rset = stmt.executeQuery ("select person from tab1"); 
while (rset.next()) 
{ 
  Object s = rset.getObject(1, PersonFactory.getOracleDataFactory());
  if (s != null) 
  { 
    if (s instanceof Person) 
      System.out.println ("This is a Person"); 
    else if (s instanceof Student) 
      System.out.println ("This is a Student"); 
    else if (s instanceof ParttimeStudent) 
      System.out.pritnln ("This is a PartimeStudent"); 
    else 
      System.out.println ("Unknown type"); 
  } 
}

Creating Subtype Objects

There are cases where JDBC applications create database subtype objects with JDBC drivers. These objects are sent either to the database as bind variables or are used to exchange information within the JDBC application.

With customized mapping, the JDBC application creates either SQLData-based or OracleData-based objects, depending on the approach you choose, to represent database subtype objects. With default mapping, the JDBC application creates STRUCT objects to represent database subtype objects. All the data fields inherited from the supertype as well as all the fields defined in the subtype must have values. The following code demonstrates this:

Connection conn = ...   // make a JDBC connection 
...
Object[] attrs = { 
  new Integer(1234), "HR", "500 Oracle Parkway", // data fields defined in
                                                    // PERSON_T 
  new Integer(102), "CS",                           // data fields defined in
                                                    // STUDENT_T 
  new Integer(4)                                    // data fields defined in
                                                    // PARTTIMESTUDENT_T 
}; 
Struct s = conn.createStruct("HR.PARTTIMESTUDENT", attrs);

s is initialized with data fields inherited from PERSON_T and STUDENT_T, and data fields defined in PARTTIMESTUDENT_T.

Sending Subtype Objects

In a typical JDBC application, a Java object that represents a database object is sent to the databases as one of the following:

• A data manipulation language (DML) bind variable

• A PL/SQL IN parameter

• An object type attribute value

The Java object can be an instance of the STRUCT class or an instance of the class implementing either the SQLData or OracleData interface. Oracle JDBC driver will convert the Java object into the linearized format acceptable to the database SQL engine. Binding a subtype object is the same as binding a standard object.

Accessing Subtype Data Fields

While the logic to access subtype data fields is part of the customized class, this logic for default mapping is defined in the JDBC application itself. The database objects are returned as instances of the oracle.jdbc.OracleStruct class. The JDBC application needs to call one of the following access methods in the STRUCT class to access the data fields:

• Object[] getAttribute()

• oracle.sql.Datum[] getOracleAttribute()

Subtype Data Fields from the getAttribute Method

The getAttribute method of the java.sql.Struct interface is used in JDBC 2.0 to access object data fields. This method returns a java.lang.Object array, where each array element represents an object attribute. You can determine the individual element type by referencing the corresponding attribute type in the JDBC conversion matrix. For example, a SQL NUMBER attribute is converted to a java.math.BigDecimal object. The getAttribute method returns all the data fields defined in the supertype of the object type as well as data fields defined in the subtype. The supertype data fields are listed first followed by the subtype data fields.

Subtype Data Fields from the getOracleAttribute Method

The getOracleAttribute method is an Oracle extension method and is more efficient than the getAttribute method. The getOracleAttribute method returns an oracle.sql.Datum array to hold the data fields. Each element in the oracle.sql.Datum array represents an attribute. You can determine the individual element type by referencing the corresponding attribute type in the Oracle conversion matrix. For example, a SQL NUMBER attribute is converted to an oracle.sql.NUMBER object. The getOracleAttribute method returns all the attributes defined in the supertype of the object type, as well as attributes defined in the subtype. The supertype data fields are listed first followed by the subtype data fields.

The following code shows the use of the getAttribute method:

// tab1.person column can store PERSON_T, STUDENT_T and PARTIMESTUDENT_T objects 
ResultSet rset = stmt.executeQuery ("select person from tab1"); 
while (rset.next()) 
{ 
  oracle.sql.STRUCT s = (oracle.sql.STRUCT) rset.getObject(1); 
  if (s != null) 
  { 
    String sqlname = s.getSQLTypeName(); 

    Object[] attrs = s.getAttribute(); 

    if (sqlname.equals ("HR.PERSON") 
    { 
      System.out.println ("ssn="+((BigDecimal)attrs[0]).intValue()); 
      System.out.println ("name="+((String)attrs[1])); 
      System.out.println ("address="+((String)attrs[2])); 
    } 
    else if (sqlname.equals ("HR.STUDENT")) 
    { 
      System.out.println ("ssn="+((BigDecimal)attrs[0]).intValue()); 
      System.out.println ("name="+((String)attrs[1])); 
      System.out.println ("address="+((String)attrs[2])); 
      System.out.println ("deptid="+((BigDecimal)attrs[3]).intValue()); 
      System.out.println ("major="+((String)attrs[4])); 
    } 
    else if (sqlname.equals ("HR.PARTTIMESTUDENT")) 
    { 
      System.out.println ("ssn="+((BigDecimal)attrs[0]).intValue()); 
      System.out.println ("name="+((String)attrs[1])); 
      System.out.println ("address="+((String)attrs[2])); 
      System.out.println ("deptid="+((BigDecimal)attrs[3]).intValue()); 
      System.out.println ("major="+((String)attrs[4])); 
      System.out.println ("numHours="+((BigDecimal)attrs[5]).intValue()); 
    } 
    else 
      throw new Exception ("Invalid type name: "+sqlname); 
  } 
} 
rset.close (); 
stmt.close (); 
conn.close ();

Inheritance Metadata Methods

Oracle JDBC drivers provide a set of metadata methods to access inheritance properties. The inheritance metadata methods are defined in the oracle.sql.StructDescriptor and oracle.jdbc.StructMetaData classes.

The StructMetaData class provides inheritance metadata methods for subtype attributes. The getMetaData method of the StructDescriptor class returns an instance of StructMetaData of the type. The StructMetaData class contains the following inheritance metadata methods:

JPublisher Functionality

You can direct JPublisher to create custom object classes that implement either the SQLData interface or the OracleData interface, according to how you set the JPublisher type mappings.

If you use the OracleData interface, then JPublisher will also create a custom reference class to map to object references for the Oracle object type. If you use the SQLData interface, then JPublisher will not produce a custom reference class. You would use standard java.sql.Ref instances instead.

If you want additional functionality, you can subclass the custom object class and add features as desired. When you run JPublisher, there is a command-line option for specifying both a generated class name and the name of the subclass you will implement. For the SQL-Java mapping to work properly, JPublisher must know the subclass name, which is incorporated into some of the functionality of the generated class.

JPublisher Type Mappings

JPublisher offers various choices for how to map user-defined types and their attribute types between SQL and Java. This section lists categories of SQL types and the mapping options available for each category.

Categories of SQL Types

JPublisher categorizes SQL types into the following groups, with corresponding JPublisher options as specifies:

• User-defined types (UDT)

  This includes Oracle objects, references, and collections. You use the JPublisher -usertypes option to specify the type-mapping implementation for UDTs, either a standard SQLData implementation or an Oracle-specific OracleData implementation.

• Numeric types

  This includes anything stored in the database as the NUMBER SQL type. You use the JPublisher -numbertypes option to specify type-mapping for numeric types.

• Large object (LOB) types

  This includes the SQL types, BLOB and CLOB. You use the JPublisher -lobtypes option to specify type-mapping for LOB types.

• Built-in types

  This includes anything stored in the database as a SQL type not covered by the preceding categories. For example, CHAR, VARCHAR2, LONG, and RAW. You use the JPublisher -builtintypes option to specify type-mapping for built-in types.

Type-Mapping Modes

JPublisher defines the following type-mapping modes, two of which apply to numeric types only:

• JDBC mapping (setting jdbc)

  Uses standard default mappings between SQL types and Java native types. For a custom object class, uses a SQLData implementation.

• Oracle mapping (setting oracle)

  Uses corresponding oracle.sql types to map to SQL types. For a custom object, reference, or collection class, uses an OracleData implementation.

• Object-JDBC mapping (setting objectjdbc)

  Is an extension of the JDBC mapping. Where relevant, object-JDBC mapping uses numeric object types from the standard java.lang package, such as java.lang.Integer, Float, and Double, instead of primitive Java types, such as int, float, and double. The java.lang types are nullable, while the primitive types are not.

• BigDecimal mapping (setting bigdecimal)

  Uses java.math.BigDecimal to map to all numeric attributes. This is appropriate if you are dealing with large numbers but do not want to map to the oracle.sql.NUMBER class.

  Note:

  Using BigDecimal mapping can significantly degrade performance.

Mapping the Oracle object type to Java

Use the JPublisher -usertypes option to determine how JPublisher will implement the custom Java class that corresponds to an Oracle object type:

• A setting of -usertypes=oracle, which is the default setting, instructs JPublisher to create an OracleData implementation for the custom object class. This will also result in JPublisher producing an OracleData implementation for the corresponding custom reference class.

• A setting of -usertypes=jdbc instructs JPublisher to create a SQLData implementation for the custom object class. No custom reference class can be created. You must use java.sql.Ref, oracle.jdbc.OracleRef, or oracle.sql.REF for the reference type.

Mapping Attribute Types to Java

If you do not specify mappings for the attribute types of the Oracle object type, then JPublisher uses the following defaults:

• For numeric attribute types, the default mapping is object-JDBC.

• For LOB attribute types, the default mapping is Oracle.

• For built-in type attribute types, the default mapping is JDBC.

If you want alternate mappings, then use the -numbertypes, -lobtypes, and -builtintypes options, as necessary, depending on the attribute types you have and the mappings you desire.

If an attribute type is itself an Oracle object type, then it will be mapped according to the -usertypes setting.

Summary of SQL Type Categories and Mapping Settings

Table 13-1 summarizes JPublisher categories for SQL types, the mapping settings relevant for each category, and the default settings.

Functionality for Getting Object Metadata

The oracle.sql.StructDescriptor class includes functionality to retrieve metadata about a structured object type. The StructDescriptor class has a getMetaData method with the same functionality as the standard getMetaData method available in result set objects. It returns a set of attribute information, such as attribute names and types. Call this method on a StructDescriptor object to get metadata about the Oracle object type that the StructDescriptor object describes.

The signature of the StructDescriptor class getMetaData method is the same as the signature specified for getMetaData in the standard ResultSet interface. The signature is as follows:

ResultSetMetaData getMetaData() throws SQLException

However, this method actually returns an instance of oracle.jdbc.StructMetaData, a class that supports structured object metadata in the same way that the standard java.sql.ResultSetMetaData interface specifies support for result set metadata.

The following method is also supported by StructMetaData:

String getOracleColumnClassName(int column) throws SQLException

This method returns the fully qualified name of the oracle.sql.Datum subclass whose instances are manufactured if the OracleResultSet interface getOracleObject method is called to retrieve the value of the specified attribute. For example, oracle.sql.NUMBER.

To use the getOracleColumnClassName method, you must cast the ResultSetMetaData object, which that was returned by the getMetaData method, to StructMetaData.

• Note:

  In all the preceding method signatures, column is something of a misnomer. Where you specify a value of 4 for column, you really refer to the fourth attribute of the object.

Steps for Retrieving Object Metadata

Use the following steps to obtain metadata about a structured object type:

1. Create or acquire a StructDescriptor instance that describes the relevant structured object type.

2. Call the getMetaData method on the StructDescriptor instance.

3. Call the metadata getter methods, getColumnName, getColumnType, and getColumnTypeName, as desired.

   Note:

   If one of the structured object attributes is itself a structured object, repeat steps 1 through 3.

Example

The following method shows how to retrieve information about the attributes of a structured object type. This includes the initial step of creating a StructDescriptor instance.

// 
// Print out the ADT's attribute names and types 
// 
void getAttributeInfo (Connection conn, String type_name) throws SQLException 
{ 
  // get the type descriptor 
  StructDescriptor desc = StructDescriptor.createDescriptor (type_name, conn); 

  // get type metadata 
  ResultSetMetaData md = desc.getMetaData (); 

  // get # of attrs of this type 
  int numAttrs = desc.length (); 

  // temporary buffers 
  String attr_name; 
  int attr_type; 
  String attr_typeName; 

  System.out.println ("Attributes of "+type_name+" :"); 
  for (int i=0; i<numAttrs; i++) 
  { 
    attr_name = md.getColumnName (i+1); 
    attr_type = md.getColumnType (i+1); 
    System.out.println (" index"+(i+1)+" name="+attr_name+" type="+attr_type); 

    // drill down nested object 
    if (attrType == OracleTypes.STRUCT) 
    { 
      attr_typeName = md.getColumnTypeName (i+1); 

      // recursive calls to print out nested object metadata 
      getAttributeInfo (conn, attr_typeName); 
    } 
  } 
}