How to read from BLOB and Write to a file in user readable format.

Question

Hi,
     I am trying to read from a BLOB column and write the content to a file in user readable format. So far I was able to read the Blob column using dbms_lob, but not able to write to a file. Kindly let me know the method to do this.

Answer 1

Hi, with this Java Code from Oracle Technet it's a easy thing:
// classpath= /ORACLE/u01/app/oracle/product/10.2.0.3/jdbc/lib/ojdbc14.jar
// Java SQL classes
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
// Oracle JDBC driver class
import oracle.jdbc.OracleDriver;
// Java IO classes
import java.io.IOException;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
//Java Util classes
import java.util.Properties;
* This class demonstrates the Oracle JDBC 10g enhanced features for inserting
* and retrieving CLOB data from the database. Using the new features, large
* data of more than 32765 bytes can be inserted into the database using the
* existing PreparedStatement.setString() and PreparedStatement.getString()
* methods.
public class ClobMan {
/* Database Connection object */
private Connection conn = null;
/* Variables to hold database details */
private String url = null;
private String user = null;
private String password = null;
// Create a property object to hold the username, password and
// the new property SetBigStringTryClob.
private Properties props = new Properties();
/* String to hold file name */
private String fileName = null;
* Default Constructor to instantiate and get a handle to class methods
* and variables.
public ClobMan(String fileName) {
this.fileName = fileName;
* Main runnable class.
public static void main(String[] args) throws SQLException {
// Instantiate the main class.
ClobMan clobMan = new ClobMan(args[0]);
// Load the Oracle JDBC driver class.
DriverManager.registerDriver(new OracleDriver());
// Load the database details into the variables.
String dbUrl = "jdbc:oracle:thin:@pmol:1550:dbpmol";
clobMan.url = dbUrl;
clobMan.user = "gh10";
clobMan.password = "secret";
// Populate the property object to hold the username, password and
// the new property 'SetBigStringTryClob' which is set to true. Setting
// this property allows inserting of large data using the existing
// setString() method, to a CLOB column in the database.
clobMan.props.put("user", clobMan.user );
clobMan.props.put("password", clobMan.password);
clobMan.props.put("SetBigStringTryClob", "true");
// Check if the table 'CLOB_TAB' is present in the database.
//clobMan.checkTables();
// Call the methods to insert and select CLOB from the database.
//clobMan.insertClob();
clobMan.selectClob();
* This method will insert the data into a CLOB column in the database.
* Oracle JDBC 10g has enhanced the existing PreparedStatement.setString()
* method for setting the data more than 32765 bytes. So, using setString(),
* it is now easy to insert CLOB data into the database directly.
private void insertClob() throws SQLException {
// Create a PreparedStatement object.
PreparedStatement pstmt = null;
try {
// Create the database connection, if it is closed.
if ((conn==null)||conn.isClosed()){
// Connect to the database.
conn = DriverManager.getConnection( this.url, this.props );
// Create SQL query to insert data into the CLOB column in the database.
String sql = "INSERT INTO clob_tab VALUES(?)";
// Read a big file(larger than 32765 bytes)
String str = this.readFile();
// Create the OraclePreparedStatement object
pstmt = conn.prepareStatement(sql);
// Use the same setString() method which is enhanced to insert
// the CLOB data. The string data is automatically transformed into a
// clob and inserted into the database column. Make sure that the
// Connection property - 'SetBigStringTryClob' is set to true for
// the insert to happen.
pstmt.setString(1,str);
// Execute the PreparedStatement
pstmt.executeUpdate();
} catch (SQLException sqlex) {
// Catch Exceptions and display messages accordingly.
System.out.println("SQLException while connecting and inserting into " +
"the database table: " + sqlex.toString());
} catch (Exception ex) {
System.out.println("Exception while connecting and inserting into the" +
" database table: " + ex.toString());
} finally {
// Close the Statement and the connection objects.
if (pstmt!=null) pstmt.close();
if (conn!=null) conn.close();
* This method reads the CLOB data from the database by using getString()
* method.
private void selectClob() throws SQLException {
// Create a PreparedStatement object
PreparedStatement pstmt = null;
// Create a ResultSet to hold the records retrieved.
ResultSet rset = null;
try {
// Create the database connection, if it is closed.
if ((conn==null)||conn.isClosed()){
// Connect to the database.
conn = DriverManager.getConnection( this.url, this.props );
// Create SQL query statement to retrieve records having CLOB data from
// the database.
String sqlCall = "SELECT rownum, name, sourcetext FROM t_source";
pstmt= conn.prepareStatement(sqlCall);
// Execute the PrepareStatement
rset = pstmt.executeQuery();
String rownum = null;
String o_name =null;
String clobVal = null;
// Get the CLOB value from the resultset
//java.io.BufferedWriter out = new java.io.BufferedWriter(new java.io.FileWriter("pr_all.sql"));
while (rset.next()) {
rownum = rset.getString(1);
     o_name = rset.getString(2);
     clobVal = rset.getString(3);
System.out.println(" length: "+clobVal.length()+" "+o_name+" "+rownum);
     java.io.BufferedWriter out =
     new java.io.BufferedWriter(new java.io.FileWriter(o_name+".prc"));
     out.write(clobVal);
     out.newLine();
     out.write("/");
     out.newLine();
     out.newLine();
out.flush();
out.close();
} catch (SQLException sqlex) {
// Catch Exceptions and display messages accordingly.
System.out.println("SQLException while connecting and querying the " +
"database table: " + sqlex.toString());
} catch (Exception ex) {
System.out.println("Exception while connecting and querying the " +
"database table: " + ex.toString());
} finally {
// Close the resultset, statement and the connection objects.
if (rset !=null) rset.close();
if (pstmt!=null) pstmt.close();
if (conn!=null) conn.close();
* Method to check if the table ('CLOB_TAB') exists in the database; if not
* then it is created.
* Table Name: CLOB_TAB
* Column Name Type
* col_col CLOB
private void checkTables() {
Statement stmt = null;
ResultSet rset = null;
try {
// Create the database connection, if it is closed.
if ((conn==null)||conn.isClosed()){
// Connect to the database.
conn = DriverManager.getConnection( this.url, this.props );
// Create Statement object
stmt = conn.createStatement();
// Check if the table is present
rset = stmt.executeQuery(" SELECT table_name FROM user_tables "+
" WHERE table_name = 'CLOB_TAB' ");
// If the table is not present, then create the table.
if (!rset.next()) {
// Table does not exist, create it
stmt.executeUpdate(" CREATE TABLE clob_tab(clob_col CLOB)");
} catch (SQLException sqlEx) {
System.out.println("Could not create table clob_tab : "
+sqlEx.toString());
} finally {
try {
if( rset != null ) rset.close();
if( stmt != null ) stmt.close();
if (conn!=null) conn.close();
} catch(SQLException ex) {
System.out.println("Could not close objects in checkTables method : "
+ex.toString());
* This method reads the specified text file and, returns the content
* as a string.
private String readFile()
throws FileNotFoundException, IOException{
// Read the file whose content has to be passed as String
BufferedReader br = new BufferedReader(new FileReader(fileName));
String nextLine = "";
StringBuffer sb = new StringBuffer();
while ((nextLine = br.readLine()) != null) {
sb.append(nextLine);
// Convert the content into to a string
String clobData = sb.toString();
// Return the data.
return clobData;
}