how to use oracle clob data type which java?

Oracle provides some hints like this.

Example demonstrating the use of the JDBC 2.0 Clob
and Blob classes.  With the Oracle JDBC drivers version 8.1.6, these classes
can be used in place of oracle.sql.CLOB and oracle.sql.BLOB respectively.
The example requires the 8.1.6 JDBC driver (classes12.zip) to be used with
JDK version 1.2.  The program is written to connect via the thin driver.  You
need to update the connect string as appropriate for your database.

To run the program, first create the following table and data as scott/tiger:

create table test_lob (c1 number, c2 clob, c3 blob);

insert into test_lob values (10, 'This is some text for a clob column',
           utl_raw.cast_to_raw('This is some text for a blob column'));

Then ensure that you have your CLASSPATH pointing to JDK1.2 and classes12.zip.


References
----------

"Oracle8i JDBC Developer's Guide and Reference", (A64685-01)


Source Code
-----------

/*
 *  This example uses the JDK 1.2 (JDBC 2.0) Clob and Blob classes.  To
 *  build and run this program, you must use the 1.2 compiler and have the
 *  8.1.6 JDBC driver with classes12.zip on your classpath (not
 *  classes111.zip).
 *
 *  The example uses the following table and data:
 *
 *    create table test_lob (c1 number, c2 clob, c3 blob);
 *
 *    insert into test_lob values (10, 'This is some text for a clob column',
 *               utl_raw.cast_to_raw('This is some text for a blob column'));
 */

import java.sql.*;
import oracle.jdbc.driver.*;
import java.io.*;

public class selectLobs
{
   public static void main ( String args [] ) throws SQLException
   {
      Connection   conn;
      String       stmt;
      Clob         c_lob;
      Blob         b_lob;
      Reader       chr_instream;             // Unicode clob reader
      InputStream  raw_instream;              // Blob reader
      char         chr_buffer[];                 // Clob buffer
      byte         raw_buffer[];                 // Blob buffer
      String       out_buffer;                   // For binary -> String


      // Select for update so we can also write data.
      stmt = "select c1, c2, c3 from test_lob for update";

      try
      {
         // Connect.
         DriverManager.registerDriver( new oracle.jdbc.driver.OracleDriver() );
         conn = DriverManager.getConnection( "jdbc:oracle:thin:@s692:1521:V816",
                                             "scott","tiger" );
         
         // Turn off autocommit.
         conn.setAutoCommit( false );

         // Prepare the statement.
         PreparedStatement pstmt = conn.prepareStatement( stmt );

         // Execute.
         ResultSet results = pstmt.executeQuery();

         // Output the data.
         results.next();
         System.out.println( results.getInt( 1 ) );

         // Get the Clob contents.  Read as a single chunk using streaming.  
         // (If we were to read in a loop then we would read until -1 is
         // returned.)
         c_lob = results.getClob( 2 );
         chr_buffer = new char[(int)c_lob.length()];
         raw_buffer = new byte[(int)c_lob.length()*4];

         // First get as an ascii stream (byte array).
         raw_instream = c_lob.getAsciiStream();
         raw_instream.read( raw_buffer );

         // Need to convert from a byte array to a String so can output.
         out_buffer = new String( raw_buffer );
         System.out.println( out_buffer );
         raw_instream.close();

         // Now get as a unicode stream.
         chr_instream = c_lob.getCharacterStream();
         chr_instream.read( chr_buffer );
         System.out.println( chr_buffer );
         chr_instream.close();        

         // Get the Blob contents.
         b_lob = results.getBlob( 3 );
         raw_buffer = new byte[(int)b_lob.length()];

         // First via streaming as a single chunk.
         raw_instream = b_lob.getBinaryStream();
         raw_instream.read( raw_buffer );

         out_buffer = new String( raw_buffer );
         System.out.println( out_buffer );
         raw_instream.close();

         // Now directly as a byte array.
       raw_buffer = b_lob.getBytes( 1, (int)b_lob.length() );
         out_buffer = new String( raw_buffer );
         System.out.println( out_buffer );

         // Writing data to Lobs:
         // There are no methods to do this with java.sql.Clob/Blob.  
         //
         // For oracle.sql.CLOB there is getAsciiOutputStream() to write via
         // an ascii stream and getCharacterOutputStream() to write via a
         // unicode one, plus putChars() to write a char array and putString()
         // to write a String - both at a given position within the Clob.  For
         // oracle.sql.BLOB there is getBinaryOutputStream() and putBytes().  
         // There are also oracle.jdbc.driver classes to do similar that
         // take oracle.sql.CLOB/BLOB as appropriate, namely:
         //       OracleBlobOutputStream()
         //       OracleClobOutputStream()
         //       OracleClobWriter()
         // (Note all three classes have corresponding input/reader classes.)
         //
         // Hence to write data to the lobs here it is necessary to cast the
         // Clob and Blob to oracle.sql.CLOB and oracle.sql.BLOB respectively
         // and use one of the methods listed above.  E.g. to append to the
         // clob column:
         ((oracle.sql.CLOB)c_lob).putString( (int)c_lob.length()+1, "\nBye!" );

         // To check the data has been input correctly read it back via the
         // getSubString() method.  Note, unlike CLOB, Clob has no getChars()
         // method to return data as a char array.
         System.out.println( c_lob.getSubString( 1, (int)c_lob.length() ) );
         
         results.close();
         pstmt.close();

         // Commit.
         conn.commit();
      }
      catch ( Exception e )
      {
        System.out.println( "\nError occurred:\n" + e + "\n" );
      }
   }
}


Sample Output
-------------

10
This is some text for a clob column
This is some text for a clob column
This is some text for a blob column
This is some text for a blob column
This is some text for a clob column
Bye!