JDBC Tutorials - Herong's Tutorial Examples - Version 2.21, by Dr. Herong Yang

Retrieving CLOB Values with getClob() Method

This section describes how to retrieve CLOB values with the ResultSet.getClob() method.

If you like to work with java.sql.Clob objects, you can retrieve CLOB values with the getClob() method on ResultSet objects. The Clob object offers some interesting methods:

  • length() - Returns the number of characters in the Clob object. The return value has a type of "long". You may need to convert it to "int" to be used in other motheds.
  • getSubString(long pos, int length) - Returns a substring of characters from the Clob object with a specified starting position and length. Note the start position is "long" value, but the length is "int" value.
  • getCharacterStream() - Returns a Reader object from the Clob object so that you can read the content as a stream.
  • free() - Releases the resources that the Clob object holds. This was added in JDBC 4.0 (Java 1.6).

Here is my test program on getClob() method:

/**
 * OracleClobGetClob.java
 * Copyright (c) 2007 by Dr. Herong Yang. All rights reserved.
 */
import java.io.*;
import java.sql.*;
public class OracleClobGetClob {
  public static void main(String [] args) {
    Connection con = null;
    try {
      oracle.jdbc.pool.OracleDataSource ds 
        = new oracle.jdbc.pool.OracleDataSource();
      ds.setDriverType("thin");
      ds.setServerName("localhost");
      ds.setPortNumber(1521);
      ds.setDatabaseName("XE");
      ds.setUser("Herong");
      ds.setPassword("TopSecret");
      con = ds.getConnection();

// Retrieving CLOB value with getClob()
      Statement sta = con.createStatement(); 
      ResultSet res = sta.executeQuery("SELECT * FROM Article"); 
      int i = 0;
      while (res.next() && i<3) {
        i++;
        System.out.println("Record ID: "+res.getInt("ID"));
        System.out.println("   Subject = "+res.getString("Subject"));
        Clob bodyOut = res.getClob("Body");
        int length = (int) bodyOut.length();
        System.out.println("   Body Size = "+length);
        String body = bodyOut.getSubString(1, length);
        if (body.length() > 100) body = body.substring(0,100);
        System.out.println("   Body = "+body+"...");
//      bodyOut.free(); // new in JDBC 4.0
      }
      res.close();

      sta.close();
      con.close();
    } catch (Exception e) {
      System.err.println("Exception: "+e.getMessage());
      e.printStackTrace();
    }
  }
}

The output confirms that the getClob() method and Clob objects are not hard to use:

C:\>java -cp .;\local\lib\ojdbc14.jar OracleClobGetClob

Record ID: 1
   Subject = Test on INSERT statement
   Body Size = 84
   Body = A BLOB (Binary Large OBject) is a large chunk of data 
which is stored in a database....

Record ID: 2
   Subject = Test of the setString() method
   Body Size = 304
   Body = He is wonderful and strange and who knows how old he is, 
he thought. Never have I had such a strong...

Record ID: 3
   Subject = Test of setCharacterStream() methods
   Body Size = 2232
   Body = /**
 * OracleClobSetCharacterStream.java
 * Copyright (c) 2007 by Dr. Herong Yang. All rights reserv...

Table of Contents

 About This Book

 JDBC (Java Database Connectivity) Introduction

 Downloading and Installing JDK - Java SE

 Installing and Running Java DB - Derby

 Derby (Java DB) JDBC Driver

 Derby (Java DB) JDBC DataSource Objects

 Java DB (Derby) - DML Statements

 Java DB (Derby) - ResultSet Objects of Queries

 Java DB (Derby) - PreparedStatement

 MySQL Installation on Windows

 MySQL JDBC Driver (MySQL Connector/J)

 MySQL - PreparedStatement

 MySQL - Reference Implementation of JdbcRowSet

 MySQL - JBDC CallableStatement

 MySQL CLOB (Character Large Object) - TEXT

 MySQL BLOB (Binary Large Object) - BLOB

 Oracle Express Edition Installation on Windows

 Oracle JDBC Drivers

 Oracle - Reference Implementation of JdbcRowSet

 Oracle - PreparedStatement

 Oracle - JBDC CallableStatement

Oracle CLOB (Character Large Object) - TEXT

 Overview of CLOB (Character Large Object)

 Create Tables with CLOB Columns

 Inserting CLOB Values with SQL INSERT Statements

 Inserting CLOB Values with setString() Method

 Inserting CLOB Values with setCharacterStream() Method

 Closing InputStream Too Early on setCharacterStream()

 Retrieving CLOB Values with getString() Method

 Retrieving CLOB Values with getCharacterStream() Method

Retrieving CLOB Values with getClob() Method

 Inserting CLOB Values with setClob() Method

 Oracle BLOB (Binary Large Object) - BLOB

 Microsoft SQL Server 2005 Express Edition

 Microsoft JDBC Driver for SQL Server - sqljdbc.jar

 Microsoft JDBC Driver - Query Statements and Result Sets

 Microsoft JDBC Driver - DatabaseMetaData Object

 Microsoft JDBC Driver - DDL Statements

 Microsoft JDBC Driver - DML Statements

 SQL Server - PreparedStatement

 SQL Server CLOB (Character Large Object) - TEXT

 SQL Server BLOB (Binary Large Object) - BLOB

 JDBC-ODBC Bridge Driver - sun.jdbc.odbc.JdbcOdbcDriver

 JDBC-ODBC Bridge Driver - Flat Text Files

 JDBC-ODBC Bridge Driver - MS Access

 JDBC-ODBC Bridge Driver - MS SQL Server

 Summary of JDBC Drivers and Database Servers

 Additional Tutorial Notes to Be Added

 References

 PDF Printing Version

Retrieving CLOB Values with getClob() Method - Updated in 2014, by Dr. Herong Yang