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Servlet Example To Display Mysql Clob Data


What is Clob? 

A Clob is a Character Large Object in a Database. Clob can be very large depending on the Database up to 4 GB. It is a rich data type of JDBC. A large character data file can be stored as CLOB type. JDBC provides java.sql.Clob interface for handling large character/text object.

Mysql Clob

According to the Mysql, there are four text types TINYTEXT, TEXT, MEDIUMTEXT and LONGTEXT which can be taken as CLOB type and have the maximum lengths and storage requirements. The maximum length of TINYTEXT has 255 character (8 bits), TEXT has 16,535 character (16 bits), MEDIUMTEXT has 16,777,216 character (24 bits) and LONGTEXT has 4,294,967,295 character (32 bits).

How to define Clob Datatype in Mysql Table

In the table below, you can see "Body" field as "longtext" type in the table "article". Here, Body field represents Clob data.

CREATE TABLE `article` ( 
             `ID` int(11) NOT NULL, 
              `Subject` varchar(256) NOT NULL, 
              `Body` longtext, 
              PRIMARY KEY (`ID`) 

Display Mysql Clob Data

We have developed a servlet (DisplayClobExample) that accepts the ID of a file and displays the associated file.


import java.io.IOException;
import java.sql.Clob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DisplayClobExample extends HttpServlet {
  public void doGet(HttpServletRequest request, HttpServletResponse response
    throws IOException,ServletException{
    Clob clobFile = null;
    Connection con = null;
    Statement stmt = null;
    ResultSet rs = null;

    Integer id = 1;
    String query = "select Body from article where id = " + id;
    ServletOutputStream out = response.getOutputStream();
    out.println("<html><head><title>Display Clob Example</title></head>");
    try {
      con =DriverManager.getConnection ("jdbc:mysql://",
      stmt = con.createStatement();
      rs = stmt.executeQuery(query);
      if (rs.next()) {
        clobFile = rs.getClob(1);
      else {
        out.println("<body><h4><font color='red'>There are no any File on id="
        + id + "</font></h4></body></html>");
      long length = clobFile.length();
      String fileData = clobFile.getSubString(1(intlength);
      out.println("<body><h4><font color='green'>Successfully Display The Record:
    catch (Exception e) {
      out.println("<body><h4><font color='red'>Unable to display" 
        + e.getMessage()"</font></h4></body></html>");
    finally {
      try {
      catch (SQLException e) {

Mapping of servlet (DisplayClobExample) in web.xml


Run the servlet (DisplayClobExample) by url: http://localhost:8080/JavaExample/DisplayClobExample . The data of the file will be displayed as below:

and if in case any error in database connection exists and there is no file on given id then the following message will be displayed.

Download Source Code


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