The ResultSet interface provides the method named getClob() to retrieve clob datatype from a table in a database. In addition to this it also provides a method named getCharacterStream()
Like getClob() this method also accepts 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 unlike the getClob() method (which returns a Clob object) this method returns an object of the Reader class.
Example
Assume we have created a table named MyData 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 large textual data in it with name JavaFX. Following program retrieves the contents of the table MyData using the getString() and getCharacterStream() methods.
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 RetrievingClob_CharStream {
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 a Statement object
Statement stmt = con.createStatement();
//retrieving the data
ResultSet rs = stmt.executeQuery("select * from MyData");
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 r = clob.getCharacterStream();
String filePath = "E:\\Data\\clob_output"+j+".txt";
FileWriter writer = new FileWriter(filePath);
int i;
while ((i=r.read())!=-1) {
writer.write(i);
}
writer.close();
System.out.println(filePath);
j++;
}
}
}Output
Connection established...... Contents of the table...... JavaFX E:\Data\clob_output0.txt
If you observe the file in the obtained path you can see the contents of the Clob retrieved from the table as shown below:
