BEA Home | Events | Solutions | Partners | Products | Services | Download | Developer Center | WebSUPPORT
| WebLogic Server Doc Home | WebLogic jDriver for Oracle | Previous Topic | Next Topic | Contents | View as PDF

Advanced Oracle Features

This section presents advanced Oracle features:

- Allowing Mixed Case Metadata

- Data Types

- WebLogic Server and Oracle's NUMBER Column

- Using Oracle Long Raw Data Types

- Waiting on Oracle Resources

- Support for JDBC Extended SQL

- Overview of JDBC 2.0 for Oracle

- Configuration Required to Support JDBC 2.0

- BLOBs and CLOBs

- Character and ASCII Streams

- New Date Methods

Allowing Mixed Case Metadata

WebLogic Server supports the setting of the allowMixedCaseMetaData property. When set to the boolean true, this property sets up the Connection such that mixed case is used in calls to DatabaseMetaData methods. If this property is set to false, Oracle defaults to UPPERCASE for database metadata.

The following sample code shows how to set up the properties to include this feature:

>     Properties props = new Properties();
>     props.put("user",                   "scott");
>     props.put("password",               "tiger");
>     props.put("server",                 "DEMO");
>     props.put("allowMixedCaseMetaData", "true");

>     Driver myDriver = (Driver)
>       Class.for.Name(weblogic.jdbc.oci.Driver).newInstance();

>     Connection conn =
>        myDriver.connect("jdbc:weblogic:oracle", props);

If you do not set this property, WebLogic Server defaults to the Oracle default, and UPPERCASE is used for database metadata.

Data Types

The following table shows the recommended mapping between Oracle data types and Java types. There are additional possibilities for representing Oracle data types in Java. If the getObject() method is called when result sets are being processed, it returns the default Java data type for the Oracle column being queried.

Figure 5-1 Oracle Types Mapped to WebLogic Server

Oracle | WebLogic Server
Varchar | String
Number | Tinyint
Number | Smallint
Number | Integer
Number | Long
Number | Float
Number | Numeric
Number | Double
Long | Longvarchar
RowID | String
Date | Timestamp
Raw | (var)Binary
Long raw | Longvarbinary
Char | (var)Char
Boolean* | Number OR Varchar
MLS label | String
Blob | Blob
Clob | Clob

* Note that when PreparedStatement.setBoolean() is called, it converts a VARCHAR type to 1 or 0 (string), and it converts a NUMBER type to 1 or 0 (number).

WebLogic Server and Oracle's NUMBER Column

Oracle provides a column type called NUMBER, which can be optionally specified with a precision and a scale, in the forms NUMBER(P) and NUMBER(P,S). Even in the simple unqualified NUMBER form, this column can hold all number types from small integer values to very large floating point numbers, with high precision.

WebLogic Server reliably converts the values in a column to the Java type requested when a WebLogic Server application asks for a value from such a column. Of course, if a value of 123.456 is asked for with getInt(), the value will be rounded.

The method getObject(), however, poses a little more complexity. WebLogic Server guarantees to return a Java object which will represent any value in a NUMBER column with no loss in precision. This means that a value of 1 can be returned in an Integer, but a value like 123434567890.123456789 can only be returned in a BigDecimal.

There is no metadata from Oracle to report the maximum precision of the values in the column, so WebLogic Server must decide what sort of object to return based on each value. This means that one ResultSet may return multiple Java types from getObject() for a given NUMBER column. A table full of integer values may all be returned as Integer from getObject(), whereas a table of floating point measurements may be returned primarily as Double, with some Integer if any value happens to be something like "123.00". Oracle does not provide any information to distinguish between a NUMBER value of "1" and a NUMBER of "1.0000000000".

There is some more reliable behavior with qualified NUMBER columns, that is, those defined with a specific precision. Oracle's metadata provides these parameters to the driver so WebLogic Server will always return a Java object appropriate for the given precision and scale, regardless of the values in the table.

Column Definition | Returned by getObject()
NUMBER(P <= 9) | Integer
NUMBER(P <= 18) | Long
NUMBER(P = 19) | BigDecimal
NUMBER(P <=16, S 0) | Double
NUMBER(P = 17, S 0) | BigDecimal

Using Oracle Long Raw Data Types

There are two properties available for use with WebLogic Server in support of Oracle's chunking of Blobs, Clobs, Long, and Long raw data types. Although Blob and Clob data types are only supported with Oracle Version 8 and JDBC 2.0, these properties also apply to Oracle's Long raw data type, which is available in Oracle Version 7.

Waiting on Oracle Resources

Note: The waitOnResources() method is not supported for use with the Oracle 8 API.

The WebLogic Server driver supports Oracle's oopt() C functionality, which allows a client to wait until resources become available. The Oracle C function sets options in cases in which requested resources are not available, such as whether to wait for locks.

A developer can specify whether a client will wait for DBMS resources, or will receive an immediate exception. The following code is an excerpt from a sample code file (examples/jdbc/oracle/waiton.java):

>     java.util.Properties props = new java.util.Properties();
>     props.put("user",     "scott");
>     props.put("password", "tiger");
>     props.put("server",   "myserver");

>     Driver myDriver = (Driver)
>       Class.forName("weblogic.jdbc.oci.Driver").newInstance();

>     // You must cast the Connection as a weblogic.jdbc.oci.Connection
>     // to take advantage of this extension

>     Connection conn =(weblogic.jdbc.oci.Connection)
>       myDriver.connect("jdbc:weblogic:oracle", props);

>     // After constructing the Connection object, immediately call
>     // the waitOnResources method

>     conn.waitOnResources(true);

Use of this method can cause several error return codes to be generated while the software waits for internal resources that are locked for short durations.

To take advantage of this feature, you must do the following:

1. Cast your Connection object as a weblogic.jdbc.oci.Connection.

2. Call the waitOnResources() method.

This functionality is described in section 4-97 of The OCI Functions for C.

Autocommit

The default transaction mode for JDBC WebLogic Server assumes autocommit to be true. You can improve the performance of your programs by setting autocommit to false, after creating a Connection object, with the following statement:

>        Connection.setAutoCommit(false);

Transaction Isolation Levels

WebLogic Server supports the following transaction isolation levels:

- SET TRANSACTION ISOLATION LEVEL READ COMMITTED

- SET TRANSACTION ISOLATION LEVEL SERIALIZABLE

The Oracle DBMS supports only these two isolation levels. Unlike other JDBC drivers, WebLogic Server throws an exception if you try to use an isolation level that is unsupported. Some drivers silently ignore attempts to set an unsupported isolation level.

The READ_UNCOMMITTED transaction isolation level is not supported.

Codeset Support

JDBC and the WebLogic Server driver handle character strings in Java as Unicode strings. Because the Oracle DBMS uses a different codeset, the driver must convert character strings from Unicode to the codeset used by Oracle. The WebLogic Server examines the value stored in the Oracle environment variable NLS_LANG and selects a codeset for the JDK to use for the conversion, using the mapping shown in Table 5-1. If the NLS_LANG variable is not set, or if it is set to a codeset not recognized by the JDK, the driver cannot determine the correct codeset. (For information about the correct syntax for setting NLS_LANG, see your Oracle documentation.)

If you are converting codesets, you should pass the following property to the WebLogic Server with the Driver.connect() method when you establish the connection in your code:

>     props.put("weblogic.oci.min_bind_size", 660);

This property defines the minimum size of buffers to be bound. The default is 2000 bytes, which is also the maximum value. If you are converting codesets, you should use this property to reduce the bind size to a maximum of 660, one-third of the maximum 2000 bytes, since Oracle codeset conversion triples the buffer to allow for expansion.

WebLogic Server provides the weblogic.codeset property to set the codeset from within your Java code. For example, to use the cp863 codeset, create a Properties object and set the weblogic.codeset property before calling Driver.connect(), as shown in the following example:

>     java.util.Properties props = new java.util.Properties();
>     props.put("weblogic.codeset", "cp863");
>     props.put("user", "scott");
>     props.put("password", "tiger");

>     String connectUrl = "jdbc:weblogic:oracle";

>     Driver myDriver = (Driver)
>      Class.forName("weblogic.jdbc.oci.Driver").newInstance();

>     Connection conn =
>          myDriver.connect(connectUrl, props);

Codeset support can vary with different JVMs. Check the documentation for the JDK you are using to determine whether a particular codeset is supported.

Note: You must also set the NLS_LANG environment variable in your Oracle client to the same or a corresponding codeset.

Table 5-1 NLS_LANG Settings Mapped to JDK Codesets

NLS_LANG | JDK codeset
al24utffss | UTF8
al32utf8 | UTF8
ar8iso8859p6 | ISO8859_6
cdn8pc863 | Cp863
cl8iso8859p5 | ISO8859_5
cl8maccyrillic | MacCyrillic
cl8mswin1251 | Cp1251
ee8iso8859p2 | ISO8859_2
ee8macce | MacCentralEurope
ee8maccroatian | MacCroatian
ee8mswin1250 | Cp1250
ee8pc852 | Cp852
el8iso8859p7 | ISO8859_7
el8macgreek | MacGreek
el8mswin1253 | Cp1253
el8pc737 | Cp737
is8macicelandic | MacIceland
is8pc861 | Cp861
iw8iso8859p8 | ISO8859_8
ja16euc | EUC_JP
ja16sjis | SJIS
ko16ksc5601 | EUC_KR
lt8pc772 | Cp772
lt8pc774 | Cp774
n8pc865 | Cp865
ne8iso8859p10 | ISO8859_10
nee8iso8859p4 | ISO8859_4
ru8pc855 | Cp855
ru8pc866 | Cp866
se8iso8859p3 | ISO8859_3
th8macthai | MacThai
tr8macturkish | MacTurkish
tr8pc857 | Cp857
us7ascii | ASCII
us8pc437 | Cp437
utf8 | UTF8
we8ebcdic37 | Cp1046
we8ebcdic500 | Cp500
we8iso8859p1 | ISO8859_1
we8iso8859p15 | ISO8859_15_FDIS
we8iso8859p9 | ISO8859_9
we8macroman8 | MacRoman
we8pc850 | Cp850
we8pc860 | Cp860
zht16big5 | Big5

Support for Oracle Array Fetches

WebLogic Server supports Oracle array fetches. When called for the first time, ResultSet.next() retrieves an array of rows (rather than a single row) and stores it in memory. Each time that next() is called subsequently, it reads a row from the rows in memory until they are exhausted, and only then will next() go back to the database.

You set a property (java.util.Property) to control the size of the array fetch. The property is weblogic.oci.cacheRows; it is set by default to 100. Here's an example of setting this property to 300, which means that calls to next() only hit the database once for each 300 rows retrieved by the client.

>     Properties props = new Properties();
>     props.put("user",                   "scott");
>     props.put("password",               "tiger");
>     props.put("server",                 "DEMO");
>     props.put("weblogic.oci.cacheRows", "300");

>     Driver myDriver = (Driver)
>       Class.forName("weblogic.jdbc.oci.Driver").newInstance();

>     Connection conn = myDriver.connect("jdbc:weblogic:oracle", props);

You can improve client performance and lower the load on the database server by taking advantage of this JDBC extension. Caching rows in the client, however, requires client resources. You should tune your application for the best balance between performance and client resources, depending upon your network configuration and your application.

If any columns in a SELECT are of type LONG, BLOB, or CLOB, WebLogic Server temporarily resets the cache size to 1 for the ResultSet associated with that select statement.

Using Stored Procedures

This section describes variations in the implementation of stored procedures that are specific to Oracle.

- Binding a Parameter to an Oracle Cursor

- Notes on Using CallableStatement

Binding a Parameter to an Oracle Cursor

WebLogic has created an extension to JDBC (weblogic.jdbc.oci.CallableStatement) that allows you to bind a parameter for a stored procedure to an Oracle cursor. You can create a JDBC ResultSet object with the results of the stored procedure. This allows you to return multiple ResultSets in an organized way. The ResultSets are determined at run time in the stored procedure.

Here is an example. First define the stored procedures as follows:

>     create or replace package
>     curs_types as
>     type EmpCurType is REF CURSOR RETURN emp%ROWTYPE;
>     end curs_types;
>     /

>     create or replace procedure
>     single_cursor(curs1 IN OUT curs_types.EmpCurType,
>     ctype in number) AS BEGIN
>       if ctype = 1 then
>         OPEN curs1 FOR SELECT * FROM emp;
>       elsif ctype = 2 then
>         OPEN curs1 FOR SELECT * FROM emp where sal  2000;
>       elsif ctype = 3 then
>         OPEN curs1 FOR SELECT * FROM emp where deptno = 20;
>       end if;
>     END single_cursor;
>     /
>     create or replace procedure
>     multi_cursor(curs1 IN OUT curs_types.EmpCurType,
>                  curs2 IN OUT curs_types.EmpCurType,
>                  curs3 IN OUT curs_types.EmpCurType) AS
>     BEGIN
>         OPEN curs1 FOR SELECT * FROM emp;
>         OPEN curs2 FOR SELECT * FROM emp where sal  2000;
>         OPEN curs3 FOR SELECT * FROM emp where deptno = 20;
>     END multi_cursor;
>     /

In your Java code, you'll construct CallableStatements with the stored procedures and register the output parameter as data type java.sql.Types.OTHER. When you retrieve the data into a ResultSet, use the output parameter index as an argument for the getResultSet() method.

>       java.sql.CallableStatement cstmt = conn.prepareCall(
>                            "BEGIN OPEN ? " +
>                            "FOR select * from emp; END;");
>       cstmt.registerOutParameter(1, java.sql.Types.OTHER);

>       cstmt.execute();
>       ResultSet rs = cstmt.getResultSet(1);
>       printResultSet(rs);
>       rs.close();
>       cstmt.close();

>       java.sql.CallableStatement cstmt2 = conn.prepareCall(
>                            "BEGIN single_cursor(?, ?); END;");
>       cstmt2.registerOutParameter(1, java.sql.Types.OTHER);

>       cstmt2.setInt(2, 1);
>       cstmt2.execute();
>       rs = cstmt2.getResultSet(1);
>       printResultSet(rs);

>       cstmt2.setInt(2, 2);
>       cstmt2.execute();
>       rs = cstmt2.getResultSet(1);}
>       printResultSet(rs);

>       cstmt2.setInt(2, 3);
>       cstmt2.execute();
>       rs = cstmt2.getResultSet(1);
>       printResultSet(rs);
>       cstmt2.close();

>       java.sql.CallableStatement cstmt3 = conn.prepareCall(
>                              "BEGIN multi_cursor(?, ?, ?); END;");
>       cstmt3.registerOutParameter(1, java.sql.Types.OTHER);
>       cstmt3.registerOutParameter(2, java.sql.Types.OTHER);
>       cstmt3.registerOutParameter(3, java.sql.Types.OTHER);

>       cstmt3.execute();

>       ResultSet rs1 = cstmt3.getResultSet(1);
>       ResultSet rs2 = cstmt3.getResultSet(2);
>       ResultSet rs3 = cstmt3.getResultSet(3);

For the full code for this example, including the printResultSet() method, see the examples in the samples/examples/jdbc/oracle/ directory.

Note that the default size of an Oracle stored procedure string is 256K.

Notes on Using CallableStatement

The default length of a string bound to an OUTPUT parameter of a CallableStatement is 128 characters. If the value you assign to the bound parameter exceeds that length, you'll get the following error:

>     ORA-6502: value or numeric error

You can adjust the length of the value of the bound parameter by passing an explicit length with the scale argument to the CallableStatement.registerOutputParameter() method. Here is a code example that binds a VARCHAR that will never be larger than 256 characters:

>       CallableStatement cstmt =
>         conn.prepareCall("BEGIN testproc(?); END;");

>       cstmt.registerOutputParameter(1, Types.VARCHAR, 256);
>       cstmt.execute();
>       System.out.println(cstmt.getString());
>       cstmt.close();

DatabaseMetaData Methods

This section describes some variations in the implementation of DatabaseMetaData methods that are specific to Oracle:

- As a general rule, the String catalog argument is ignored in all DatabaseMetaData methods.

- In the DatabaseMetaData.getProcedureColumns() method:

  - The String catalog argument is ignored.

  - The String schemaPattern argument accepts only exact matches (no pattern matching).

  - The String procedureNamePattern argument accepts only exact matches (no pattern matching).

  - The String columnNamePattern argument is ignored.

Support for JDBC Extended SQL

The JavaSoft JDBC specification includes SQL Extensions, also called SQL Escape Syntax. All WebLogic jDrivers support Extended SQL. Extended SQL provides access to common SQL extensions in a way that is portable between DBMSs.

For example, the function to extract the day name from a date is not defined by the SQL standards. For Oracle, the SQL is:

>       select to_char(date_column, 'DAY') from table_with_dates

The equivalent function for Sybase and Microsoft SQL Server is:

>       select datename(dw, date_column) from table_with_dates

Using Extended SQL, you can retrieve the day name for both DBMSs as follows:

>       select {fn dayname(date_column)} from table_with_dates

Here's an example that demonstrates several features of Extended SQL:

>       String query =
>       "-- This SQL includes comments and " +
>           "JDBC extended SQL syntax.\n" +
>       "select into date_table values( \n" +
>       "      {fn now()},        -- current time \n" +
>       "      {d '1997-05-24'},  -- a date       \n" +
>       "      {t '10:30:29' },   -- a time       \n" +
>       "      {ts '1997-05-24 10:30:29.123'},  -- a timestamp\n" +
>       "     '{string data with { or } will not be altered}'\n" +
>       "-- Also note that you can safely include" +
>          " { and } in comments or\n" +
>       "-- string data.";
>       Statement stmt = conn.createStatement();
>       stmt.executeUpdate(query);

Extended SQL is delimited with curly braces ("{}") to differentiate it from common SQL. Comments are preceded by two hyphens, and are ended by a new line ("\n"). The entire Extended SQL sequence, including comments, SQL, and Extended SQL, is placed within double quotes and passed to the execute() method of a Statement object. Here is Extended SQL used as part of a CallableStatement:

>        CallableStatement cstmt =
>         conn.prepareCall("{ ? = call func_squareInt(?)}");

This example shows that you can nest extended SQL expressions:

>        select {fn dayname({fn now()})}

You can retrieve lists of supported Extended SQL functions from a DatabaseMetaData object. This example shows how to list all the functions a JDBC driver supports:

>        DatabaseMetaData md = conn.getMetaData();
>        System.out.println("Numeric functions:     " +
>           md.getNumericFunctions());
>       System.out.println("\nString functions:    " +
>           md.getStringFunctions());
>       System.out.println("\nTime/date functions: " +
>           md.getTimeDateFunctions());
>       System.out.println("\nSystem functions:    " +
>           md.getSystemFunctions());
>       conn.close();

Overview of JDBC 2.0 for Oracle

The following JDBC 2.0 features are implemented in WebLogic jDriver for Oracle:

- BLOBs (Binary Large Objects)—WebLogic Server can now handle this Oracle data type.

- CLOBs (Character Large Objects)—WebLogic Server can now handle this Oracle data type.

- Character Streams for both ASCII and Unicode characters—A better way to handle characters streams, as streams of characters instead of as byte arrays.

- Batch Updates—You can now send multiple statements to the database as a single unit.

These features have been added to the existing JDBC functionality previously available in the WebLogic Server. All of your existing code for previous drivers will work with the new WebLogic jDriver for Oracle.

Configuration Required to Support JDBC 2.0

Since WebLogic Server Version 6.1 runs on JDK 1.3.1, this provides the Java 2 environment required by JDBC 2.0. For a complete list of supported configurations, see the WebLogic Platform support page.

BLOBs and CLOBs

The BLOB (Binary Large Object) and CLOB (Character Large Object) data types were made available with the release of Oracle version 8. The JDBC 2.0 specification and WebLogic Server also support these data types. This section contains information about using these data types.

Note: Please note the following limitation: You cannot use BLOBs and CLOBs when using the RMI driver in conjunction with the WebLogic jDriver for Oracle. BLOB and CLOB's are not serializable and therefore not supported with the JDBC RMI Driver used with WebLogic 6.x.

Transaction Boundaries

BLOBs and CLOBs in Oracle behave differently than other data types in regards to transactional boundaries (statements issued before an SQL commit or rollback statement). in that a BLOB or CLOB will be come inactive as soon as a transaction is committed. If AutoCommit is set to TRUE, the transaction will be automatically committed after each command issued on the connection, including SELECT statements. For this reason you will need to set AutoCommit to false if you need to have a BLOB or CLOB available across multiple SQL statements. You will then need to manually commit (or rollback) the transactions at the appropriate time. To set AutoCommit to false, enter the following command:

>     conn.setAutoCommit(false); // where conn is your connection object

BLOBs

The BLOB data type, available with Oracle version 8, allows you to store and retrieve large binary objects in an Oracle table. Although BLOBs are defined as part of the JDBC 2.0 specification, the specification does not provide methods to update BLOB columns in a table. The BEA WebLogic implementation of BLOBs, however, does provide this functionality by means of an extension to JDBC 2.0.

Connection Properties

  weblobic.oci.selectBlobChunkSize

  This property sets the size of an internal buffer used for sending bytes or characters to an I/O stream. When the Chunk size is reached, the driver will perform an implicit flush() operation, which will cause the data to be sent to the DBMS.

  Explicitly setting this value can be useful in controlling memory usage on the client.

  If the value of this property is not explicitly set, a default value of 65534 will be used.

  Set this property by passing it to the Connection object as a property. For example, this code fragment sets weblobic.oci.selectBlobChunkSize to 1200:

  Properties props = new Properties();
  props.put("user", "scott");
  props.put("password", "tiger");
  props.put("server", "DEMO");

  props.put ("weblobic.oci.selectBlobChunkSize","1200");

  Driver myDriver = (Driver)
  Class.forName("weblogic.jdbc.oci.Driver").newInstance();

  Connection conn =
  driver.connect("jdbc:weblogic:oracle:myServer", props);

  weblogic.oci.insertBlobChunkSize

  This property specifies the buffer size (in bytes) of input streams used internally by the driver.

  Set this property to a positive integer to insert Blobs into an Oracle DBMS with the Blob chunking feature. By default, this property is set to zero (0), which means that BLOB chunking is turned off.

Import Statements

To use the BLOB functionality described in this section, import the following classes in your client code:

>     import java.sql.*;
>     import java.util.*;
>     import java.io.*;
>     import weblogic.jdbc.common.*;

Initializing a BLOB Field

When you first insert a row containing a BLOB data type, you must insert the row with an "empty" BLOB before the field can be updated with real data. You can insert an empty BLOB with the Oracle EMPTY_BLOB() function.

To initialize a BLOB field:

1. Create a table with one or more columns defined as a BLOB data type.

2. Insert a new row with an empty BLOB column, using the Oracle EMPTY_BLOB() function:

   >     stmt.execute("INSERT into myTable values (1,EMPTY_BLOB()");

3. Obtain a "handle" to the BLOB column:

   >     java.sql.Blob myBlob = null;
   >     Statement stmt2 = conn.createStatement();
   >     stmt2.execute("SELECT myBlobColumn from myTable
   >       where pk = 1 for update");
   >     ResultSet rs = stmt2.getResultSet();
   >     rs.next() {
   >       myBlob = rs.getBlob("myBlobColumn");
   >       // do something with the BLOB
   >     }

4. You can now write data to the BLOB. Continue with the next section, Writing Binary Data to a BLOB.

Writing Binary Data to a BLOB

To write binary data to a BLOB column:

1. Obtain a handle to the BLOB field as described above, in Initializing a BLOB Field, step 3.

2. Create an InputStream object containing the binary data.

   >     java.io.InputStream is = // create your input stream

3. Create an output stream to which you write your BLOB data. Note that you must cast your BLOB object to weblogic.jdbc.common.OracleBlob.

   >     java.io.OutputStream os =
   >     ((weblogic.jdbc.common.OracleBlob)
   >     myBlob).getBinaryOutputStream();

4. Write the input stream containing your binary data to the output stream. The write operation is finalized when you call the flush() method on the OutputStream object.

   >     byte[] inBytes = new byte[65534]; // see note below
   >     		int numBytes = is.read(inBytes);
   >     while (numBytes > 0) {
   >       os.write(inBytes, 0, numBytes);
   >       numBytes = is.read(inBytes);
   >     }
   >     os.flush();

   Note: The value [65534] in the above code presumes that you have not set the weblogic.oci.select.BlobChunkSize property whose default is 65534. If you have set this property, setting the byte[] value to match the value set in the weblogic.oci.select.BlobChunkSize property will provide the most efficient handling of the data. For more information about this property, see Connection Properties.

5. Clean up:

   >     os.close();
   >     pstmt.close();
   >     conn.close();

Writing a BLOB Object

Writing a BLOB object to a table is performed with Prepared Statements. For example, to write the myBlob object to the table myOtherTable:

>     PreparedStatement pstmt = conn.preparedStatement(
>         "UPDATE myOtherTable SET myOtherBlobColumn = ? WHERE id = 12");

>     pstmt.setBlob(1, myBlob);

Updating a CLOB Value Using a Prepared Statement

If you use a prepared statement to update a CLOB and the new value is shorter than the previous value, the CLOB will retain the characters that were not specifically replaced during the update. For example, if the current value of a CLOB is abcdefghij and you update the CLOB using a prepared statement with zxyw, the value in the CLOB is updated to zxywefghij. To correct values updated with a prepared statement, you should use the dbms_lob.trim procedure to remove the excess characters left after the update. See the Oracle documentation for more information about the dbms_lob.trim procedure.

Reading BLOB Data

When you retrieve a BLOB column with the getBlob() method and then use a ResultSet from a SQL SELECT statement, only a pointer to the BLOB data is returned; the binary data is not actually transferred to the client until the getBinaryStream() method is called and the data is read into the stream object.

To read BLOB data from an Oracle table:

1. Execute a SELECT statement:

   >     stmt2.execute("SELECT myBlobColumn from myTable");

2. Use the results from the SELECT statement.

   >     int STREAM_SIZE = 10;
   >     byte[] r = new byte[STREAM_SIZE];

   >     ResultSet rs = stmt2.getResultSet();
   >     java.sql.Blob myBlob = null;
   >     while (rs.next) {
   >       myBlob = rs.getBlob("myBlobColumn");

   >      java.io.InputStream readis = myBlob.getBinaryStream();

   >      for (int i=0 ; i < STREAM_SIZE ; i++) {
   >           r[i] = (byte) readis.read();
   >          System.out.println("output [" + i + "] = " + r[i]);
   >      }

3. Clean up:

   >     rs.close();
   >     stmt2.close();

Note: You can also use a CallableStatement to generate a ResultSet. This ResultSet can then be used as shown above. See your JDK documentation under java.sql.CallableStatment for details.

Other Methods

The following methods of the java.sql.Blob interface are also implemented in the WebLogic Server JDBC 2.0 driver. For details, see your JDK documentation:

- getBinaryStream()

- getBytes()

- length()

The position() method is not implemented.

CLOBs

The CLOB data type, available with Oracle version 8, enables storage of large character strings in an Oracle table. Since the JDBC 2.0 specification does not include functionality to directly update CLOB columns, BEA has implemented the methods getAsciiOutputStream() (for ASCII data) and getCharacterOutputStream() (for Unicode data) to insert or update a CLOB.

Codeset Support

Depending on which version of the Oracle Server and client you are using you may need to set one of the following properties by passing them to the Connection object when you establish your connection the DBMS in your Java client code.

  weblogic.codeset

  This property allows you to set a codeset from within your Java code. You must also set the NLS_LANG Oracle environment variable.

  weblogic.oci.ncodeset

  This property sets the National codeset used by the Oracle server. You must also set the NLS_NCHAR Oracle environment variable.

  weblogic.oci.codeset_width

  This property tells the WebLogic Server which type you are using.

  Possible Values:

  0 for variable-width codesets

  1 for fixed-width codesets (1 is is the default value)

  2 or 3 for the width, in bytes, of the codeset

  weblogic.oci.ncodeset_width

  If you are using one of Oracle's National codesets, specify the width of that codeset with this property.

  Possible Values:

  0 for variable-width codesets

  1 for fixed-width codesets (1 is the default value)

  2 or 3 for the width, in bytes, of the codeset

Initializing a CLOB Field

When you first insert a row containing a CLOB data type, you must insert the row with an "empty" CLOB before the field can be updated with real data. You can insert an empty CLOB with the Oracle EMPTY_CLOB() function.

To initialize a CLOB column:

1. Create a table with one or more columns defined as a CLOB data type.

2. Insert a new row with an empty CLOB column, using the Oracle EMPTY_CLOB() function:

   >     stmt.execute("INSERT into myTable VALUES (1,EMPTY_CLOB()");

3. Obtain an object for the CLOB column:

   >     java.sql.Clob myClob = null;
   >     Statement stmt2 = conn.createStatement();
   >     stmt2.execute("SELECT myClobColumn from myTable
   >       where pk = 1 for update");
   >     ResultSet rs = stmt2.getResultSet();
   >     while (rs.next) {
   >       myClob = rs.getClob("myClobColumn");
   >     }

4. You can now write character data to the CLOB. If your data is in the ASCII format, Continue with the next section, Writing ASCII Data to a CLOB. If your character data is in Unicode format, see Writing Unicode Data to a CLOB

Writing ASCII Data to a CLOB

To write ASCII character data to a CLOB column:

1. Obtain a "handle" to the CLOB as described above, in Initializing a CLOB Field, step 3.

2. Create an object containing the character data:

   >     String s = // some ASCII data

3. Create an ASCII output stream to which you write your CLOB characters. Note that you must cast your CLOB object to weblogic.jdbc.common.OracleClob.

   >     java.io.OutputStream os =
   >     ((weblogic.jdbc.common.OracleClob)
   >     myclob).getAsciiOutputStream();

4. Write the input stream containing your ASCII data to the output stream. The write operation is finalized when you call the flush() method on the OutputStream object.

   >     byte[] b = s.getBytes("ASCII");

   >     os.write(b);
   >     os.flush();

5. Clean up:

   >     os.close();
   >     pstmt.close();
   >     conn.close();

Writing Unicode Data to a CLOB

To write Unicode character data to a CLOB column:

1. Obtain a "handle" to the CLOB as described earlier, in step 3 of "Initializing a CLOB Field."

2. Create an object containing the character data:

   >     String s = // some Unicode character data

3. Create a character output stream to which you write your CLOB characters. Note that you must cast your CLOB object to weblogic.jdbc.common.OracleClob.

   >     java.io.Writer wr =
   >     ((weblogic.jdbc.common.OracleClob)
   >     myclob).getCharacterOutputStream();

4. Write the input stream containing your ASCII data to the output stream. The write operation is finalized when you call the flush() method on the OutputStream object.

   >     char[] b = s.toCharArray(); // converts 's' to a character array

   >     wr.write(b);
   >     wr.flush();

5. Clean up:

   >     wr.close();
   >     pstmt.close();
   >     conn.close();

Writing CLOB Objects

Writing a CLOB object to a table is performed with Prepared Statements. For example, to write the myClob object to the table myOtherTable:

>     PreparedStatement pstmt = conn.preparedStatement(
>         "UPDATE myOtherTable SET myOtherClobColumn = ? WHERE id = 12");

>     pstmt.setClob(1, myClob);

Reading CLOB Data

When a CLOB column is retrieved using a result set from a SQL SELECT statement, only a pointer to the CLOB data is returned; the actual data is not transferred to the client with the result set until the getAsciiStream() method is called and the characters are read in to the stream.

To read CLOB data from an Oracle table:

1. Execute a SELECT statement:

   >     java.sql.Clob myClob = null;
   >     Statement stmt2 = conn.createStatement();
   >     stmt2.execute("SELECT myClobColumn from myTable");

2. Use the results from the SELECT statement:

   >     ResultSet rs = stmt2.getResultSet();

   >     while (rs.next) {
   >       myClob = rs.getClob("myClobColumn");
   >       java.io.InputStream readClobis =
   >           myReadClob.getAsciiStream();
   >       char[] c = new char[26];
   >       for (int i=0 ; i < 26  ; i++) {
   >           c[i] = (char) readClobis.read();
   >           System.out.println("output [" + i + "] = " + c[i]);
   >       }
   >     }

3. Clean up:

   >     rs.close();
   >     stmt2.close();

Note: You can also use a CallableStatement to generate a ResultSet. This ResultSet can then be used as shown above. See your JDK documentation under java.sql.CallableStatment for details.

Other Methods

The following methods of the java.sql.Clob interface are also implemented in the WebLogic Server (a JDBC 2.0 driver):

- getSubString()

- length()

For details about these methods, see the JDK documentation.

Note: The position() method is not implemented.

Character and ASCII Streams

Some new methods in the JDBC 2.0 specification allow character and ASCII streams to be manipulated as characters rather than as bytes, as in earlier versions. The following methods for handling character and ASCII streams are implemented in WebLogic Server.

Unicode Character Streams

  getCharacterStream()

  The java.sql.ResultSet interface uses this method for reading Unicode streams as the Java type java.io.Reader. This method replaces the deprecated getUnicodeStream() method.

  setCharacterStream()

  The java.sql.PreparedStatement interface uses this method for writing a java.io.Reader object. This method replaces the deprecated setUnicodeStream() method.

ASCII Character Streams

  getAsciiStream()

  The java.sql.ResultSet interface uses this method for reading ASCII streams as the Java type java.io.InputStream.

  setAsciiStream()

  The java.sql.PreparedStatement interface uses this method for writing a java.io.InputStream object.

For details about using these methods, see your JDK documentation.

Batch Updates

Batch updates are a feature of JDBC 2.0 that allows you to send multiple SQL update statements to the DBMS as a single unit. Depending on the application, this can provide improved performance over sending multiple update statements individually. The Batch update feature is available in the Statement interface and requires the use of SQL statements that return an update count and do not return a result set. Using Batch updates with the callableStatement or preparedStatement is not supported.

The following SQL statements can be used with Batch updates:

- INSERT INTO

- UPDATE

- DELETE

- CREATE TABLE

- DROP TABLE

- ALTER TABLE

Using Batch Updates

This is the basic procedure for using Batch updates:

1. Get a connection by using the WebLogic Server JDBC 2.0 driver as described in "Connecting to an Oracle DBMS" in Chapter 3, "Using WebLogic jDriver for Oracle." For this example, the connection object is called conn.

2. Create a statement object using the createStatement() method. For example:

   >     Statement stmt = conn.createStatement();

3. Use the addBatch() method to add SQL statements to the batch. These statements are not sent to the DBMS until the executeBatch() method is called. For example:

   >     stmt.addBatch("INSERT INTO batchTest VALUES ('JOE', 20,35)");
   >     stmt.addBatch("INSERT INTO batchTest VALUES ('Bob', 30,44)");
   >     stmt.addBatch("INSERT INTO batchTest VALUES ('Ed',  34,22)");

4. Use the executeBatch() method to send the batch to the DBMS for processing. For example:

   >     stmt.executeBatch();

   If any of the statements fail an exception is thrown, and none of the statements is executed.

Clearing the Batch

You may clear a batch of statements that was created with the addBatch() method, by using the clearBatch() method. For example:

>     stmt.clearBatch();

Update Counts

According to the JDBC 2.0 specification, the executeBatch() method should return an array of Integers containing the number of rows updated for each Statement. The Oracle DBMS, however, does not supply this information to the driver. Instead, the Oracle DBMS returns -2 for all updates.

New Date Methods

The following methods have a signature which takes a java.util.Calendar object as a parameter. java.util.Calendar allows you to specify time zone and location information that is used to translate dates. Consult your JDK API guide for details about using the java.util.Calendar class.

>     java.sql.ResultSet.getDate(int columnIndex, Calendar cal)

  (returns a java.sql.Date object)

>     java.sql.PreparedStatement.setDate
>       (int parameterIndex, Date x, Calendar cal)

Copyright © 2001 BEA Systems, Inc. All rights reserved. Required browser: Netscape 4.0 or higher, or Microsoft Internet Explorer 4.0 or higher.