How to save java objects into database in java?

Saving Java objects into database and read it back from database using JDBC

Question:- How we can write binary objects into a database table, for that what type of data type should we use for the creation of database tables?

To Map an object with relational databases and vice versa is always a difficult task.
Very good solutions for that are serialize each Java object using the object stream and preserve the result into a database as a binary blob. As this is a valid scenario and the JDBC explicitly supports to perform this.

Questions: - What is Blob data type?

Answer:-

Binary large object or basic large object: - Large object data types store data ranging in size from 0 bytes to 2 GB. A BLOB is a collection of binary data stored as a single entity in a database. This data type can store binary data larger than VARBINARY (32K limit). Blobs are typically any objects, images, audio, other multimedia objects or other types of business or application-specific data. A BLOB is a varying-length binary string that can be up to 2,147,483,647 characters long.

For storing java objects into the database we can use BLOB datatype in the table.We can create a table using below CREATE TABLE command in MYSQL database.

Table Structure for MySql Database:-

CREATE TABLE persist_java_objects (

object_id int(14) NOT NULL auto_increment,

object_name varchar(30) default NULL,

java_object blob,

PRIMARY KEY  (object_id)

)

System Requirements:-

jdk1.5 and above(I am using jdk1.7)
Eclipse Editor or other(I am using Eclipse Helios).

Required Jars:-

mysql-connector-java-5.0.4-bin.jar

Sample Example to save a List of Objects into database and read back from database :-

SaveObject2Database.java

package com.gaurav.persistjavaobjects;

import java.io.ByteArrayInputStream;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.ObjectInputStream;

import java.io.ObjectOutputStream;

import java.sql.Blob;

import java.sql.Connection;

import java.sql.DriverManager;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.util.ArrayList;

import java.util.Date;

import java.util.List;

public class SaveObject2Database {

            /** This method will help to get mysql connection from database*/   

            private static Connection getConnection() throws Exception {

                        String driver = "com.mysql.jdbc.Driver";

                        String url = "jdbc:mysql://localhost:3306/test";

                        String username = "root";

                        String password = "root";

                        Class.forName(driver);

                        Connection con = DriverManager.getConnection(url, username, password);

                        return con;

            }

                    /** This method will help to convert any object into byte array*/            

                   private static byte[] convertObjectToByteArray(Object obj) throws IOException {

                        ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();

                        ObjectOutputStream objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);

                        objectOutputStream.writeObject(obj);

                        return byteArrayOutputStream.toByteArray();

            }

                        /** This method will help to save java objects into database*/            

                         private static long saveBlob(Connection con, Object javaObject2Persist) {

                        byte[] byteArray = null;

                        PreparedStatement preparedStatement = null;

                        String SQLQUERY_TO_SAVE_JAVAOBJECT = "INSERT INTO persist_java_objects(object_name, java_object) VALUES (?, ?)";

                        int persistObjectID = -1;

                        try {

                                    byteArray = convertObjectToByteArray(javaObject2Persist);

                                    preparedStatement = con.prepareStatement(

                                                            SQLQUERY_TO_SAVE_JAVAOBJECT,

                                                            PreparedStatement.RETURN_GENERATED_KEYS);

                                    preparedStatement.setString(1, javaObject2Persist.getClass()

                                                            .getName());

                                    preparedStatement.setBytes(2, byteArray);

                                    preparedStatement.executeUpdate();

                                    System.out

                                                            .println("Query - "

                                                                                    + SQLQUERY_TO_SAVE_JAVAOBJECT

                                                                                    + " is successfully executed for Java object serialization ");

                                    //Trying to get the Generated Key

                                    ResultSet rs = preparedStatement.getGeneratedKeys();

                                    if (rs.next()) {

                                                persistObjectID = rs.getInt(1);

                                                System.out

                                                                        .println("Object ID while saving the binary object is->"

                                                                                                + persistObjectID);

                                    }

                                    preparedStatement.close();

                        } catch (SQLException e) {

                                    e.printStackTrace();

                        } catch (Exception e) {

                                    e.printStackTrace();

                        }

                        return persistObjectID;

            }

/** This method will help to read java objects from database*/               

private static byte[] getBlob(Connection con, long objectId) {

                        String SQLQUERY_TO_READ_JAVAOBJECT= "SELECT java_object FROM persist_java_objects WHERE object_id = ?;";

                        PreparedStatement pstmt = null;

                        ResultSet resultSet = null;

                        Blob blob = null;

                        byte[] bytes = null;

                        try {

                                    pstmt = con.prepareStatement(SQLQUERY_TO_READ_JAVAOBJECT);

                                    System.out.println("Reading the saved Object from the database where the object Id is:->" + objectId);

                                    pstmt.setLong(1, objectId);

                                    resultSet = pstmt.executeQuery();

                                    while (resultSet.next()) {

                                                blob = resultSet.getBlob(1);

                                    }

                                    bytes = blob.getBytes(1, (int) (blob.length()));

                        } catch (SQLException e) {

                                    e.printStackTrace();

                        } catch (Exception e) {

                                    e.printStackTrace();

                        }

                        return bytes;

            }

            @SuppressWarnings("unchecked")

            public static void main(String args[]) throws Exception {

                        Connection connection = null;

                        byte[] retrievedArrayObject = null;

                        try {

                                    connection = getConnection();

                                    List<Object> listToSaveInDB = new ArrayList<Object>();

                                    listToSaveInDB.add(new Date());

                                    listToSaveInDB.add(new String("KUMAR GAURAV"));

                                    listToSaveInDB.add(new Integer(55));

                                    long persistObjectID = saveBlob(connection, listToSaveInDB);

                                    System.out.println(listToSaveInDB + " Object is saved sucessfully");

                                    retrievedArrayObject = getBlob(connection, persistObjectID);

                                    ObjectInputStream objectInputStream = null;

                                    if (retrievedArrayObject != null)

                                                objectInputStream = new ObjectInputStream(

                                                                        new ByteArrayInputStream(retrievedArrayObject));

                                    Object retrievingObject = objectInputStream.readObject();

                                    List<Object> dataListFromDB = (List<Object>) retrievingObject;

                                    for (Object object : dataListFromDB) {

                                                System.out.println("Retrieved Data is :->" + object.toString());

                                    }

                                    System.out

                                                            .println("Successfully retrieved java Object from Database");

                        } catch (Exception e) {

                                    e.printStackTrace();

                        } finally {

                                    connection.close();

                        }

            }

}

Result:->

Query - INSERT INTO persist_java_objects(object_name, java_object) VALUES (?, ?) is successfully executed for Java object serialization
Object ID while saving the binary object is->13
[Fri Aug 02 07:17:26 IST 2013, KUMAR GAURAV, 10055] Object is saved sucessfully
Reading the saved Object from the database where the object Id is:->13
Retrieved Data is :->Fri Aug 02 07:17:26 IST 2013
Retrieved Data is :->KUMAR GAURAV
Retrieved Data is :->10055
Successfully retrieved java Object from Database
 

Table Status after insertion java objects into database:-