How can we retrieve file from database using JDBC?

The ResultSet interface provides the methods named getClob() and getCharacterStream() to retrieve Clob datatype, In which the contents of a file are typically stored.

These methods accept an integer representing the index of the column (or, a String value representing the name of the column) and retrieves the value at the specified column.

The difference is the getClob() method returns a Clob object and the getCgaracterStream() method returns a Reader object which holds the contents of the Clob datatype.

Example

Assume we have created a table named Articles in the database with the following description.

+---------+--------------+------+-----+---------+-------+
| Field   | Type         | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+-------+
| Name    | varchar(255) | YES  |     | NULL    |       |
| Article | longtext     | YES  |     | NULL    |       |
+---------+--------------+------+-----+---------+-------+

And, we have inserted three articles in it with names article 1, article 2 and, article 3 as shown below:

Example

Following program retrieves the contents of the table Articles using the getString() and getClob() methods and saves it in the specified files.

import java.io.FileWriter;
import java.io.Reader;
import java.sql.Clob;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
public class RetrievingFileFromDatabase {
   public static void main(String args[]) throws Exception {
      //Registering the Driver
      DriverManager.registerDriver(new com.mysql.jdbc.Driver());
      //Getting the connection
      String mysqlUrl = "jdbc:mysql://localhost/sampleDB";
      Connection con = DriverManager.getConnection(mysqlUrl, "root", "password");
      System.out.println("Connection established......");
      //Creating aStatement
      Statement stmt = con.createStatement();
      //Retrieving the data
      ResultSet rs = stmt.executeQuery("select * from Articles");
      int j = 0;
      System.out.println("Contents of the table are: ");
      while(rs.next()) {
         System.out.println(rs.getString("Name"));
         Clob clob = rs.getClob("Article");
         Reader reader = clob.getCharacterStream();
         String filePath = "E:\\Data\\clob_output"+j+".txt";
         FileWriter writer = new FileWriter(filePath);
         int i;
         while ((i = reader.read())!=-1) {
            writer.write(i);
         }
         writer.close();
         System.out.println(filePath);
         j++;
      }
   }
}

Output

Connection established......
Contents of the table are:
article1
E:\Data\clob_output0.txt
article2
E:\Data\clob_output1.txt
article3
E:\Data\clob_output2.txt

Krantik Chavan

Published on 22-Mar-2019 11:21:43

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