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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