JDBC Complete Notes

Create Database

The CREATE DATABASE statement is used for creating a new database. The syntax is −

Example The following SQL statement creates a Database named EMP −

SQL> CREATE DATABASE DATABASE_NAME;

SQL> CREATE DATABASE EMP;

Drop Database

The DROP DATABASE statement is used for deleting an existing database. The syntax is −

Note − To create or drop a database you should have administrator privilege on your database server. Be careful, deleting a database would loss all the data stored in the database.

SQL> DROP DATABASE DATABASE_NAME;

Create Table

The CREATE TABLE statement is used for creating a new table. The syntax is −

Example The following SQL statement creates a table named Employees with four columns −

SQL> CREATE TABLE table_name
(
   column_name column_data_type,
   column_name column_data_type,
   column_name column_data_type
   ...
);

SQL> CREATE TABLE Employees
(
   id INT NOT NULL,
   age INT NOT NULL,
   first VARCHAR(255),
   last VARCHAR(255),
   PRIMARY KEY ( id )
);

Drop Table

The DROP TABLE statement is used for deleting an existing table. The syntax is −

Example The following SQL statement deletes a table named Employees −

SQL> DROP TABLE table_name;

SQL> DROP TABLE Employees;

INSERT Data

The syntax for INSERT, looks similar to the following, where column1, column2, and so on represents the new data to appear in the respective columns −

Example The following SQL INSERT statement inserts a new row in the Employees database created earlier −

SQL> INSERT INTO table_name VALUES (column1, column2, ...);

SQL> INSERT INTO Employees VALUES (100, 18, 'Zara', 'Ali');

SELECT Data

The SELECT statement is used to retrieve data from a database. The syntax for SELECT is −

The WHERE clause can use the comparison operators such as =, !=, <, >, <=,and >=, as well as the BETWEEN and LIKE operators.

Example The following SQL statement selects the age, first and last columns from the Employees table, where id column is 100 −

The following SQL statement selects the age, first and last columns from the Employees table where first column contains Zara −

SQL> SELECT column_name, column_name, ...
  FROM table_name
  WHERE conditions;

SQL> SELECT first, last, age
  FROM Employees
  WHERE id = 100;

SQL> SELECT first, last, age
  FROM Employees
  WHERE first LIKE '%Zara%';

UPDATE Data

The UPDATE statement is used to update data. The syntax for UPDATE is −

The WHERE clause can use the comparison operators such as =, !=, <, >, <=,and >=, as well as the BETWEEN and LIKE operators.

Example The following SQL UPDATE statement changes the age column of the employee whose id is 100 −

SQL> UPDATE table_name
  SET column_name = value, column_name = value, ...
  WHERE conditions;

SQL> UPDATE Employees SET age=20 WHERE id=100;

DELETE Data

The DELETE statement is used to delete data from tables. The syntax for DELETE is −

The WHERE clause can use the comparison operators such as =, !=, <, >, <=,and >=, as well as the BETWEEN and LIKE operators.

Example The following SQL DELETE statement deletes the record of the employee whose id is 100 −

SQL> DELETE FROM table_name WHERE conditions;

SQL> DELETE FROM Employees WHERE id=100;

Which Driver should be Used?

If you are accessing one type of database, such as Oracle, Sybase, or IBM, the preferred driver type is 4. If your Java application is accessing multiple types of databases at the same time, type 3 is the preferred driver. Type 2 drivers are useful in situations, where a type 3 or type 4 driver is not available yet for your database. The type 1 driver is not considered a deployment-level driver, and is typically used for development and testing purposes only

JDBC - Database Connections

Register JDBC Driver

You must register the driver in your program before you use it. Registering the driver is the process by which the Oracle driver's class file is loaded into the memory, so it can be utilized as an implementation of the JDBC interfaces. You need to do this registration only once in your program. You can register a driver in one of two ways.

Approach I - Class.forName()

The most common approach to register a driver is to use Java's Class.forName() method, to dynamically load the driver's class file into memory, which automatically registers it. This method is preferable because it allows you to make the driver registration configurable and portable. The following example uses Class.forName( ) to register the Oracle driver −

You can use getInstance() method to work around noncompliant JVMs, but then you'll have to code for two extra Exceptions as follows −

try {
  Class.forName("oracle.jdbc.driver.OracleDriver");
}
catch(ClassNotFoundException ex) {
  System.out.println("Error: unable to load driver class!");
  System.exit(1);
}

try {
  Class.forName("oracle.jdbc.driver.OracleDriver").newInstance();
}
catch(ClassNotFoundException ex) {
  System.out.println("Error: unable to load driver class!");
  System.exit(1);
catch(IllegalAccessException ex) {
  System.out.println("Error: access problem while loading!");
  System.exit(2);
catch(InstantiationException ex) {
  System.out.println("Error: unable to instantiate driver!");
  System.exit(3);
}

Approach II - DriverManager.registerDriver()

The second approach you can use to register a driver, is to use the static DriverManager.registerDriver() method.

You should use the registerDriver() method if you are using a non-JDK compliant JVM, such as the one provided by Microsoft. The following example uses registerDriver() to register the Oracle driver −

try {
  Driver myDriver = new oracle.jdbc.driver.OracleDriver();
  DriverManager.registerDriver( myDriver );
}
catch(ClassNotFoundException ex) {
  System.out.println("Error: unable to load driver class!");
  System.exit(1);
}

Database URL Formulation

After you've loaded the driver, you can establish a connection using the DriverManager.getConnection() method. For easy reference, let me list the three overloaded DriverManager.getConnection() methods −

• getConnection(String url)
• getConnection(String url, Properties prop)
• getConnection(String url, String user, String password)

Here each form requires a database URL. A database URL is an address that points to your database. Formulating a database URL is where most of the problems associated with establishing a connection occurs. Following table lists down the popular JDBC driver names and database URL.

RDBMS JDBC driver name URL format

MySQL com.mysql.jdbc.Driver jdbc:mysql://hostname/ databaseName

ORACLE oracle.jdbc.driver.OracleDriver jdbc:oracle:thin:@hostname:port Number:databaseName

DB2 COM.ibm.db2.jdbc.net.DB2Driver jdbc:db2:hostname:port Number/databaseName

Sybase com.sybase.jdbc.SybDriver jdbc:sybase:Tds:hostname: port Number/databaseName

All the highlighted part in URL format is static and you need to change only the remaining part as per your database setup.

Create Connection Object

We have listed down three forms of DriverManager.getConnection() method to create a connection object.

String URL = "jdbc:oracle:thin:@amrood:1521:EMP";
String USER = "username";
String PASS = "password"
Connection conn = DriverManager.getConnection(URL, USER, PASS);

DriverManager.getConnection(String url);

String URL = "jdbc:oracle:thin:username/password@amrood:1521:EMP";
Connection conn = DriverManager.getConnection(URL);

DriverManager.getConnection(String url, Properties info);

Using a Database URL with a username and password

The most commonly used form of getConnection() requires you to pass a database URL, a username, and a password − Assuming you are using Oracle's thin driver, you'll specify a host:port:databaseName value for the database portion of the URL. If you have a host at TCP/IP address 192.0.0.1 with a host name of amrood, and your Oracle listener is configured to listen on port 1521, and your database name is EMP, then complete database URL would be −

jdbc:oracle:thin:@amrood:1521:EMP

Now you have to call getConnection() method with appropriate username and password to get a Connection object as follows −

String URL = "jdbc:oracle:thin:@amrood:1521:EMP";\nString USER = "username";\nString PASS = "password"

Connection conn = DriverManager.getConnection(URL, USER, PASS);

Using Only a Database URL

A second form of the DriverManager.getConnection( ) method requires only a database URL −

DriverManager.getConnection(String url);

However, in this case, the database URL includes the username and password and has the following general form −

jdbc:oracle:driver:username/password@database

So, the above connection can be created as follows −

String URL = "jdbc:oracle:thin:username/password@amrood:1521:EMP";

Connection conn = DriverManager.getConnection(URL);

Using a Database URL and a Properties Object

A third form of the DriverManager.getConnection( ) method requires a database URL and a Properties object −

DriverManager.getConnection(String url, Properties info);

A Properties object holds a set of keyword-value pairs. It is used to pass driver properties to the driver during a call to the getConnection() method. To make the same connection made by the previous examples, use the following code −

import java.util.*;

String URL = "jdbc:oracle:thin:@amrood:1521:EMP";
Properties info = new Properties( );
info.put( "user", "username" );
info.put( "password", "password" );

Connection conn = DriverManager.getConnection(URL, info);

Closing JDBC Connections

At the end of your JDBC program, it is required explicitly to close all the connections to the database to end each database session. However, if you forget, Java's garbage collector will close the connection when it cleans up stale objects. Relying on the garbage collection, especially in database programming, is a very poor programming practice. You should make a habit of always closing the connection with the close() method associated with connection object. To ensure that a connection is closed, you could provide a 'finally' block in your code. A finally block always executes, regardless of an exception occurs or not. To close the above opened connection, you should call close() method as follows −

Explicitly closing a connection conserves DBMS resources, which will make your database administrator happy.

JDBC - Statements, PreparedStatement and CallableStatement Once a connection is obtained we can interact with the database. The JDBC Statement, CallableStatement, and PreparedStatement interfaces define the methods and properties that enable you to send SQL or PL/SQL commands and receive data from your database. They also define methods that help bridge data type differences between Java and SQL data types used in a database.

The following table provides a summary of each interface's purpose to decide on the interface to use.

Interfaces Recommended Use

 Statement                 Use this for general-purpose access to your database. Useful when you are using static S\n                           statements at runtime. The Statement interface cannot accept parameters.

 PreparedStatement         Use this when you plan to use the SQL statements many times. The PreparedStatement\n                           interface accepts input parameters at runtime.

 CallableStatement         Use this when you want to access the database stored procedures. The CallableStateme\n                           interface can also accept runtime input parameters.

conn.close();

The Statement Objects

Creating Statement Object

Before you can use a Statement object to execute a SQL statement, you need to create one using the Connection object's createStatement( ) method, as in the following example −

Once you've created a Statement object, you can then use it to execute an SQL statement with one of its three execute methods.

• boolean execute (String SQL): Returns a boolean value of true if a ResultSet

object can be retrieved; otherwise, it returns false. Use this method to execute SQL DDL statements or when you need to use truly dynamic SQL.

• int executeUpdate (String SQL) − Returns the number of rows affected by the

execution of the SQL statement. Use this method to execute SQL statements for which you expect to get a number of rows affected - for example, an INSERT, UPDATE, or DELETE statement.

• ResultSet executeQuery (String SQL) − Returns a ResultSet object. Use this

method when you expect to get a result set, as you would with a SELECT statement.

Statement stmt = null;
try {
  stmt = conn.createStatement( );
  ...
}
catch (SQLException e) {
  ...
}
finally {
  ...
}

Closing Statement Object

Just as you close a Connection object to save database resources, for the same reason you should also close the Statement object. A simple call to the close() method will do the job. If you close the Connection object first, it will close the Statement object as well. However, you should always explicitly close the

Statement object to ensure proper cleanup.

For a better understanding, we suggest you to study the Statement - Example tutorial.

Statement stmt = null;
try {
  stmt = conn.createStatement( );
  ...
}
catch (SQLException e) {
  ...
}
finally {
  stmt.close();
}

The PreparedStatement Objects

The PreparedStatement interface extends the Statement interface, which gives you added functionality with a couple of advantages over a generic Statement object. This statement gives you the flexibility of supplying arguments dynamically.

Creating PreparedStatement Object

All parameters in JDBC are represented by the ? symbol, which is known as the parameter marker. You must supply values for every parameter before executing the SQL statement. The setXXX() methods bind values to the parameters, where XXX represents the Java data type of the value you wish to bind to the input parameter. If you forget to supply the values, you will receive an SQLException.

Each parameter marker is referred by its ordinal position. The first marker represents position 1, the next position 2, and so forth. This method differs from that of Java array indices, which starts at 0. All of the Statement object's methods for interacting with the database (a) execute(), (b) executeQuery(), and (c) executeUpdate() also work with the PreparedStatement object. However, the methods are modified to use SQL statements that can input the parameters.

PreparedStatement pstmt = null;
try {
  String SQL = "Update Employees SET age = ? WHERE id = ?";
  pstmt = conn.prepareStatement(SQL);
  ...
}
catch (SQLException e) {
  ...
}
finally {
  ...
}

Closing PreparedStatement Object

Just as you close a Statement object, for the same reason you should also close the

PreparedStatement object.

A simple call to the close() method will do the job. If you close the Connection object first, it will close the PreparedStatement object as well. However, you should always explicitly close the PreparedStatement object to ensure proper cleanup.

For a better understanding, let us study Prepare - Example Code.

PreparedStatement pstmt = null;
try {
  String SQL = "Update Employees SET age = ? WHERE id = ?";
  pstmt = conn.prepareStatement(SQL);
  ...
}
catch (SQLException e) {
  ...
}
finally {
  pstmt.close();
}

The CallableStatement Objects

Just as a Connection object creates the Statement and PreparedStatement objects, it also creates the CallableStatement object, which would be used to execute a call to a database stored procedure.

Creating CallableStatement Object

Suppose, you need to execute the following Oracle stored procedure −

NOTE − Above stored procedure has been written for Oracle, but we are working with MySQL database so, let us write same stored procedure for MySQL as follows to create it in EMP database −

Three types of parameters exist: IN, OUT, and INOUT. The PreparedStatement object only uses the IN parameter. The CallableStatement object can use all the three. Here are the definitions of each −

Parameter Description

IN A parameter whose value is unknown when the SQL statement is created. You bind values IN parameters with the setXXX() methods.

OUT A parameter whose value is supplied by the SQL statement it returns. You retrieve values from theOUT parameters with the getXXX() methods.

INOUT A parameter that provides both input and output values. You bind variables with the setXX methods and retrieve values with the getXXX() methods.

The following code snippet shows how to employ the Connection.prepareCall() method to instantiate a CallableStatement object based on the preceding stored procedure −

The String variable SQL, represents the stored procedure, with parameter placeholders. Using the CallableStatement objects is much like using the PreparedStatement objects. You must bind values to all the parameters before executing the statement, or you will receive an SQLException. If you have IN parameters, just follow the same rules and techniques that apply to a

PreparedStatement object; use the setXXX() method that corresponds to the Java data type you

are binding. When you use OUT and INOUT parameters you must employ an additional CallableStatement method, registerOutParameter(). The registerOutParameter() method binds the JDBC data type, to the data type that the stored procedure is expected to return. Once you call your stored procedure, you retrieve the value from the OUT parameter with the appropriate getXXX() method. This method casts the retrieved value of SQL type to a Java data type.

Closing CallableStatement Object Just as you close other Statement object, for the same reason you should also close the

CallableStatement object.

A simple call to the close() method will do the job. If you close the Connection object first, it will close the CallableStatement object as well. However, you should always explicitly close the CallableStatement object to ensure proper cleanup.

CallableStatement cstmt = null;\ntry {\n   String SQL = "{call getEmpName (?, ?)}";\n   cstmt = conn.prepareCall (SQL);\n   . . .\n}\ncatch (SQLException e) {\n   . . .\n}\nfinally {\n   cstmt.close();\n                                   }

JDBC - Result Sets The SQL statements that read data from a database query, return the data in a result set. The SELECT statement is the standard way to select rows from a database and view them in a result set. The java.sql.ResultSet interface represents the result set of a database query. A ResultSet object maintains a cursor that points to the current row in the result set. The term "result set" refers to the row and column data contained in a ResultSet object. The methods of the ResultSet interface can be broken down into three categories −

• Navigational methods − Used to move the cursor around.
• Get methods − Used to view the data in the columns of the current row

being pointed by the cursor.

• Update methods − Used to update the data in the columns of the

current row. The updates can then be updated in the underlying database as well. The cursor is movable based on the properties of the ResultSet. These properties are designated when the corresponding Statement that generates the ResultSet is created. JDBC provides the following connection methods to create statements with desired ResultSet −

• createStatement(int RSType, int RSConcurrency);
• prepareStatement(String SQL, int RSType, int RSConcurrency);
• prepareCall(String sql, int RSType, int RSConcurrency);

The first argument indicates the type of a ResultSet object and the second argument is one of two ResultSet constants for specifying whether a result set is read-only or updatable.

CREATE OR REPLACE PROCEDURE getEmpName
 (EMP_ID IN NUMBER, EMP_FIRST OUT VARCHAR) AS
BEGIN
 SELECT first INTO EMP_FIRST
 FROM Employees
 WHERE ID = EMP_ID;
END;

DELIMITER $$

DROP PROCEDURE IF EXISTS `EMP`.`getEmpName` $$
CREATE PROCEDURE `EMP`.`getEmpName`
 (IN EMP_ID INT, OUT EMP_FIRST VARCHAR(255))
BEGIN
 SELECT first INTO EMP_FIRST
 FROM Employees
 WHERE ID = EMP_ID;
END $$

DELIMITER ;

CallableStatement cstmt = null;
try {
  String SQL = "{call getEmpName (?, ?)}";
  cstmt = conn.prepareCall (SQL);
  ...
}
catch (SQLException e) {
  ...
}
finally {
  ...
}

Type of ResultSet

The possible RSType are given below. If you do not specify any ResultSet type, you will automatically get one that is TYPE_FORWARD_ONLY.

Type Description

 ResultSet.TYPE_FORWARD_ONLY              The cursor can only move forward in the result set.

 ResultSet.TYPE_SCROLL_INSENSITIVE        The cursor can scroll forward and backward, and the resul\n                                          set is not sensitive to changes made by others to the\n                                          database that occur after the result set was created.

 ResultSet.TYPE_SCROLL_SENSITIVE.         The cursor can scroll forward and backward, and the resul\n                                          set is sensitive to changes made by others to the database\n                                          that occur after the result set was created.

Concurrency of ResultSet

The possible RSConcurrency are given below. If you do not specify any Concurrency type, you will automatically get one that is CONCUR_READ_ONLY.

Concurrency Description

 ResultSet.CONCUR_READ_ONLY                       Creates a read-only result set. This is the default

 ResultSet.CONCUR_UPDATABLE                       Creates an updateable result set.

All our examples written so far can be written as follows, which initializes a

Statement object to create a forward-only, read only ResultSet object −

try {\n  Statement stmt = conn.createStatement(ResultSet.TYPE_FORWARD_ONLY,\nResultSet.CONCUR_READ_ONLY);\n}\ncatch(Exception ex) {\n  ....\n}\nfinally {\n  ....\n}

Navigating a Result Set

There are several methods in the ResultSet interface that involve moving the cursor, including −

S.N. Methods & Description

1 public void beforeFirst() throws SQLException

Moves the cursor just before the first row.

2 public void afterLast() throws SQLException

Moves the cursor just after the last row.

3 public boolean first() throws SQLException

Moves the cursor to the first row.

4 public void last() throws SQLException

Moves the cursor to the last row.

5 public boolean absolute(int row) throws SQLException

Moves the cursor to the specified row.

6 public boolean relative(int row) throws SQLException

Moves the cursor the given number of rows forward or backward, from where it is curren pointing.

7 public boolean previous() throws SQLException

Moves the cursor to the previous row. This method returns false if the previous row is off t result set.

8 public boolean next() throws SQLException

Moves the cursor to the next row. This method returns false if there are no more rows in t result set.

9 public int getRow() throws SQLException

Returns the row number that the cursor is pointing to.

10 public void moveToInsertRow() throws SQLException

Moves the cursor to a special row in the result set that can be used to insert a new row in the database. The current cursor location is remembered.

11 public void moveToCurrentRow() throws SQLException

Moves the cursor back to the current row if the cursor is currently at the insert row; otherwi this method does nothing

For a better understanding, let us study Navigate - Example Code.

Viewing a Result Set

The ResultSet interface contains dozens of methods for getting the data of the current row. There is a get method for each of the possible data types, and each get method has two versions −

• One that takes in a column name.
• One that takes in a column index.

For example, if the column you are interested in viewing contains an int, you need to use one of the getInt() methods of ResultSet −

S.N. Methods & Description

1 public int getInt(String columnName) throws SQLException

Returns the int in the current row in the column named columnName.

2 public int getInt(int columnIndex) throws SQLException

Returns the int in the current row in the specified column index. The column index starts at meaning the first column of a row is 1, the second column of a row is 2, and so on.

Similarly, there are get methods in the ResultSet interface for each of the eight Java primitive types, as well as common types such as java.lang.String, java.lang.Object, and java.net.URL. There are also methods for getting SQL data types java.sql.Date, java.sql.Time, java.sql.TimeStamp, java.sql.Clob, and java.sql.Blob. Check the documentation for more information about using these SQL data types. For a better understanding, let us study Viewing - Example Code.

Updating a Result Set

The ResultSet interface contains a collection of update methods for updating the data of a result set. As with the get methods, there are two update methods for each data type −

• One that takes in a column name.
• One that takes in a column index.

For example, to update a String column of the current row of a result set, you would use one of the following updateString() methods −

S.N. Methods & Description

1 public void updateString(int columnIndex, String s) throws SQLException

Changes the String in the specified column to the value of s.

2 public void updateString(String columnName, String s) throws SQLException

Similar to the previous method, except that the column is specified by its name instead of index.

There are update methods for the eight primitive data types, as well as String, Object, URL, and the SQL data types in the java.sql package. Updating a row in the result set changes the columns of the current row in the ResultSet object, but not in the underlying database. To update your changes to the row in the database, you need to invoke one of the following methods.

S.N. Methods & Description

1 public void updateRow()

Updates the current row by updating the corresponding row in the database.

2 public void deleteRow()

Deletes the current row from the database

3 public void refreshRow()

Refreshes the data in the result set to reflect any recent changes in the database.

4 public void cancelRowUpdates()

Cancels any updates made on the current row.

5 public void insertRow()

Inserts a row into the database. This method can only be invoked when the cursor is pointi to the insert row.

JDBC - Transactions If your JDBC Connection is in auto-commit mode, which it is by default, then every SQL statement is committed to the database upon its completion. That may be fine for simple applications, but there are three reasons why you may want to turn off the auto-commit and manage your own transactions −

• To increase performance.
• To maintain the integrity of business processes.
• To use distributed transactions.

Transactions enable you to control if, and when, changes are applied to the database. It treats a single SQL statement or a group of SQL statements as one logical unit, and if any statement fails, the whole transaction fails. To enable manual- transaction support instead of the auto-commit mode that the JDBC driver uses by default, use the Connection object's setAutoCommit() method. If you pass a boolean false to setAutoCommit( ), you turn off auto-commit. You can pass a boolean true to turn it back on again. For example, if you have a Connection object named conn, code the following to turn off auto-commit −

conn.setAutoCommit(false);

Commit & Rollback

Once you are done with your changes and you want to commit the changes then call commit() method on connection object as follows −

conn.commit( );

Otherwise, to roll back updates to the database made using the Connection named conn, use the following code −

conn.rollback( );

The following example illustrates the use of a commit and rollback object −

In this case, none of the above INSERT statement would success and everything would be rolled back. For a better understanding, let us study the Commit - Example Code.

try{
  //Assume a valid connection object conn
  conn.setAutoCommit(false);
  Statement stmt = conn.createStatement();

  String SQL = "INSERT INTO Employees " +
          "VALUES (106, 20, 'Rita', 'Tez')";
  stmt.executeUpdate(SQL);
  //Submit a malformed SQL statement that breaks
  String SQL = "INSERTED IN Employees " +
          "VALUES (107, 22, 'Sita', 'Singh')";
  stmt.executeUpdate(SQL);
  // If there is no error.
  conn.commit();
}catch(SQLException se){
  // If there is any error.
  conn.rollback();
}

Using Savepoints

The new JDBC 3.0 Savepoint interface gives you the additional transactional control. Most modern DBMS, support savepoints within their environments such as Oracle's PL/SQL. When you set a savepoint you define a logical rollback point within a transaction. If an error occurs past a savepoint, you can use the rollback method to undo either all the changes or only the changes made after the savepoint. The Connection object has two new methods that help you manage savepoints −

• setSavepoint(String savepointName) − Defines a new savepoint. It

also returns a Savepoint object.

• releaseSavepoint(Savepoint savepointName) − Deletes a savepoint.

Notice that it requires a Savepoint object as a parameter. This object is usually a savepoint generated by the setSavepoint() method. There is one rollback (String savepointName) method, which rolls back work to the specified savepoint. The following example illustrates the use of a Savepoint object −

In this case, none of the above INSERT statement would success and everything would be rolled back.

JDBC - Exceptions Handling

Exception handling allows you to handle exceptional conditions such as program- defined errors in a controlled fashion. When an exception condition occurs, an exception is thrown. The term thrown means that current program execution stops, and the control is redirected to the nearest applicable catch clause. If no applicable catch clause exists, then the program's execution ends. JDBC Exception handling is very similar to the Java Exception handling but for JDBC, the most common exception you'll deal with is java.sql.SQLException.

SQLException Methods An SQLException can occur both in the driver and the database. When such an exception occurs, an object of type SQLException will be passed to the catch clause. The passed SQLException object has the following methods available for retrieving additional information about the exception −

Method Description

getErrorCode( ) Gets the error number associated with the exception.

getMessage( ) Gets the JDBC driver's error message for an error, handled by the driver or gets the Oracle error number and message for a database error.

getSQLState( ) Gets the XOPEN SQLstate string. For a JDBC driver error, no useful information is returned from this method. For a database error, the five- digit XOPEN SQLstate code is returned. This method can return null.

getNextException( ) Gets the next Exception object in the exception chain.

printStackTrace( ) Prints the current exception, or throwable, and it's backtrace to a standard error stream.

printStackTrace(PrintStream Prints this throwable and its backtrace to the print stream you specify. s)

printStackTrace(PrintWriter Prints this throwable and it's backtrace to the print writer you specify. w)

JDBC - Stored Procedure We have learnt how to use Stored Procedures in JDBC while discussing the JDBC - Statements chapter. This chapter is similar to that section, but it would give you additional information about JDBC SQL escape syntax. Just as a Connection object creates the Statement and PreparedStatement objects, it also creates the CallableStatement object, which would be used to execute a call to a database stored procedure.

Creating CallableStatement Object Suppose, you need to execute the following Oracle stored procedure −

CREATE OR REPLACE PROCEDURE getEmpName\n (EMP_ID IN NUMBER, EMP_FIRST OUT VARCHAR) AS

BEGIN SELECT first INTO EMP_FIRST FROM Employees WHERE ID = EMP_ID; END;

NOTE − Above stored procedure has been written for Oracle, but we are working with MySQL database so, let us write same stored procedure for MySQL as follows to create it in EMP database.

DELIMITER $$

DROP PROCEDURE IF EXISTS `EMP`.`getEmpName` $$\nCREATE PROCEDURE `EMP`.`getEmpName`\n (IN EMP_ID INT, OUT EMP_FIRST VARCHAR(255))

BEGIN SELECT first INTO EMP_FIRST FROM Employees WHERE ID = EMP_ID; END $$

DELIMITER ;

Three types of parameters exist − IN, OUT, and INOUT. The PreparedStatement object only uses the IN parameter. The CallableStatement object can use all the three. Here are the definitions of each −

Parameter Description

IN A parameter whose value is unknown when the SQL statement is created. You bind values to IN parameters with the setXXX() methods.

OUT A parameter whose value is supplied by the SQL statement it returns. You retrieve values from the OUT parameters with the getXXX() methods.

INOUT A parameter that provides both input and output values. You bind variables wit the setXXX() methods and retrieve values with the getXXX() methods.

The following code snippet shows how to employ the Connection.prepareCall() method to instantiate a CallableStatement object based on the preceding stored procedure −

CallableStatement cstmt = null;\ntry {\n  String SQL = "{call getEmpName (?, ?)}";\n  cstmt = conn.prepareCall (SQL);\n  ...\n}\ncatch (SQLException e) {\n  ...\n}\nfinally {\n  ...\n}

The String variable SQL represents the stored procedure, with parameter placeholders. Using CallableStatement objects is much like using PreparedStatement objects. You must bind values to all the parameters before executing the statement, or you will receive an SQLException. If you have IN parameters, just follow the same rules and techniques that apply to a

PreparedStatement object; use the setXXX() method that corresponds to the Java

data type you are binding. When you use OUT and INOUT parameters, you must employ an additional

CallableStatement method, registerOutParameter(). The registerOutParameter()

method binds the JDBC data type to the data type the stored procedure is expected to return. Once you call your stored procedure, you retrieve the value from the OUT parameter with the appropriate getXXX() method. This method casts the retrieved value of SQL type to a Java data type.

Closing CallableStatement Object Just as you close other Statement object, for the same reason you should also close the CallableStatement object. A simple call to the close() method will do the job. If you close the Connection object first, it will close the CallableStatement object as well. However, you should always explicitly close the CallableStatement object to ensure proper cleanup.

CallableStatement cstmt = null;\ntry {\n  String SQL = "{call getEmpName (?, ?)}";\n  cstmt = conn.prepareCall (SQL);\n  ...\n}\ncatch (SQLException e) {\n  ...\n}\nfinally {\n  cstmt.close();\n}

studyWe have studied more details in the Callable - Example Code.

try{
  //Assume a valid connection object conn
  conn.setAutoCommit(false);
  Statement stmt = conn.createStatement();

 //set a Savepoint
 Savepoint savepoint1 = conn.setSavepoint("Savepoint1");
 String SQL = "INSERT INTO Employees " +
         "VALUES (106, 20, 'Rita', 'Tez')";
 stmt.executeUpdate(SQL);
 //Submit a malformed SQL statement that breaks
 String SQL = "INSERTED IN Employees " +
         "VALUES (107, 22, 'Sita', 'Tez')";
 stmt.executeUpdate(SQL);
 // If there is no error, commit the changes.
 conn.commit();

}catch(SQLException se){
  // If there is any error.
  conn.rollback(savepoint1);
}

d, t, ts Keywords

They help identify date, time, and timestamp literals. As you know, no two DBMSs represent time and date the same way. This escape syntax tells the driver to render the date or time in the target database's format. For Example −

Where yyyy = year, mm = month; dd = date. Using this syntax is March 9, 2009. Here is a simple example showing how to INSERT date in a table −

//Create a Statement object

stmt = conn.createStatement(); //Insert data ==> ID, First Name, Last Name, DOB

String sql="INSERT INTO STUDENTS VALUES" +\n       "(100,'Zara','Ali', {d '2001-12-16'})";

stmt.executeUpdate(sql);

Similarly, you can use one of the following two syntaxes, either t or ts −

Where hh = hour; mm = minute; ss = second. Using this syntax is 1:30:29 PM.

This is combined syntax of the above two syntax for 'd' and 't' to represent timestamp.

{d 'yyyy-mm-dd'}

{d '2009-09-03'}

{t 'hh:mm:ss'}

{t '13:30:29'}

{ts 'yyyy-mm-dd hh:mm:ss'}

escape Keyword

This keyword identifies the escape character used in LIKE clauses. Useful when using the SQL wildcard %, which matches zero or more characters. For example −

If you use the backslash character (\) as the escape character, you also have to use two backslash characters in your Java String literal, because the backslash is also a Java escape character.

String sql = "SELECT symbol FROM MathSymbols
        WHERE symbol LIKE '\%' {escape '\'}";
stmt.execute(sql);

fn Keyword

This keyword represents scalar functions used in a DBMS. For example, you can use SQL function length to get the length of a string −

This returns 11, the length of the character string 'Hello World'.

{fn length('Hello World')}

call Keyword

This keyword is used to call the stored procedures. For example, for a stored procedure requiring an IN parameter, use the following syntax −

For a stored procedure requiring an IN parameter and returning an OUT parameter, use the following syntax −

{call my_procedure(?)};

{? = call my_procedure(?)};

oj Keyword

This keyword is used to signify outer joins. The syntax is as follows −

{oj outer-join}

Where outer-join = table {LEFT|RIGHT|FULL} OUTERJOIN {table | outer-join} on search-condition. For example −

String sql = "SELECT Employees
        FROM {oj ThisTable RIGHT
        OUTER JOIN ThatTable on id = '100'}";
stmt.execute(sql);