Java的JDBC中Statement与CallableStatement对象实例

Java的JDBC中Statement与CallableStatement对象实例

JDBC Statement对象实例

以下是利用以下三种查询以及打开和关闭说明的例子：

boolean execute(String SQL) : 返回一个布尔值true，如果ResultSet对象可以被检索，否则返回false。使用这个方法来执行SQL DDL语句，或当需要使用真正的动态SQL。

int executeUpdate(String SQL) : 返回受影响的SQL语句执行的行数。使用此方法来执行，而希望得到一些受影响的行的SQL语句 - 例如，INSERT，UPDATE或DELETE语句。

ResultSet executeQuery(String SQL) : 返回ResultSet对象。当希望得到一个结果集使用此方法，就像使用一个SELECT语句。

基于对环境和数据库安装在前面的章节中做此示例代码已被写入。

复制下面的例子中JDBCExample.java，编译并运行，如下所示：

//STEP 1. Import required packages

import java.sql.*;

public class JDBCExample {

// JDBC driver name and database URL

static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";

static final String DB_URL = "jdbc:mysql://localhost/EMP";

// Database credentials

static final String USER = "username";

static final String PASS = "password";

public static void main(String[] args) {

Connection conn = null;

Statement stmt = null;

try{

//STEP 2: Register JDBC driver

Class.forName("com.mysql.jdbc.Driver");

//STEP 3: Open a connection

System.out.println("Connecting to database...");

conn = DriverManager.getConnection(DB_URL,USER,PASS);

//STEP 4: Execute a query

System.out.println("Creating statement...");

stmt = conn.createStatement();

String sql = "UPDATE Employees set age=30 WHERE id=103";

// Let us check if it returns a true Result Set or not.

Boolean ret = stmt.execute(sql);

System.out.println("Return value is : " + ret.toString() );

// Lhttp://et us update age of the record with ID = 103;

int rows = stmt.executeUpdate(sql);

System.out.println("Rows impacted : " + rows );

// Let us select all the records and display them.

sql = "SELECT id, first, last, age FROM Employees";

ResultSet rs = stmt.executeQuery(sql);

//STEP 5: Extract data from result set

while(rs.next()){

//Retrieve by column name

int id = rs.getInt("id");

int age = rs.getInt("age");

String first = rs.getString("first");

String last = rs.getString("last");

//Display values

System.out.print("ID: " + id);

System.out.print(", Age: " + age);

System.out.print(", First: " + first);

System.out.println(", Last: " + last);

}

//STEP 6: Clean-up environment

rs.close();

stmt.close();

conn.close();

}catch(SQLException se){

//Handle errors for JDBC

se.printStackTrace();

}catch(Exception e){

//Handle errors for Class.forName

e.printStackTrace();

}finally{

//finally block used to close resources

try{

if(stmt!=null)

stmt.close();

}catch(SQLException se2){

}// nothing we can do

try{

if(conn!=null)

conn.close();

}catch(SQLException se){

se.printStackTrace();

}//end finally try

}//end try

System.out.println("Goodbye!");

}//end main

}//end JDBCExample

现在编译上面的例子如下：

C:>javac JDBCExample.java

当运行JDBCExample，它会产生以下结果：

C:>java JDBCExample

Connecting to database...

Creating statement...

Return value is : false

Rows impacted : 1

ID: 100, Age: 18, First: Zara, Last: Ali

ID: 101, Age: 25, First: Mahnaz, Last: Fatma

ID: 102, Age: 30, First: Zaid, Last: Khan

ID: 103, Age: 30, First: Sumit, Last: Mittal

Goodbye!

JDBC CallableStatement对象实例

下面是利用CallableStatement连同下列getEmpName()的MySQL存储过程的例子：

请确定已经在EMP数据库中创建该存储过程。可以使用MySQL查询浏览器来完成它。

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 ;

基于对环境和数据库安装在前面的章节中进行，这个范例程式码已被写入。

复制下面的例子中JDBCExample.java，编译并运行，如下所示：

//STEP 1. Import required packages

import java.sql.*;

public class JDBCExample {

// JDBC driver name and database URL

static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";

static final String DB_URL = "jdbc:mysql://localhost/EMP";

// Database credentials

static final String USER = "username";

static final String PASS = "password";

public static void main(String[] args) {

Connection conn = null;

CallableStatement stmt = null;

try{

//STEP 2: Register JDBC driver

Class.forName("com.mysql.jdbc.Driver");

//STEP 3: Open a connection

System.out.println("Connecting to database...");

conn = DriverManager.getConnection(DB_URL,USER,PASS);

//STEP 4: Execute a query

System.out.println("Creating statement...");

String sql = "{call getEmpName (?, ?)}";

stmt = conn.prepareCall(sql);

//Bind IN parameter first, then bind OUT parameter

int empID = 102;

stmt.setInt(1, empID); // This would set ID as 102

// Because second parameter is OUT so register it

stmt.registerOutParameter(2, java.sql.Types.VARCHAR);

//Use execute method to run stored procedure.

System.out.println("Executing stored procedure..." );

stmt.execute();

//Retrieve employee name with getXXX method

String empName = stmt.getString(2);

System.out.println("Emp Name with ID:" +

empID + " is " + empName);

stmt.close();

conn.close();

}catch(SQLException se){

//Handle errors for JDBC

se.printStackTrace();

}catch(Exception e){

//Handle errors for Class.forName

e.printStackTrace();

}finally{

//finally block used to close resources

try{

if(stmt!=null)

stmt.close();

}catch(SQLException se2){

}// nothing we can do

try{

if(conn!=null)

conn.close();

}catch(SQLException se){

se.printStackTrace();

}//end finally try

}//end try

System.out.println("Goodbye!");

}//end main

}//end JDBCExample

现在编译上面的例子如下：

C:>javac JDBCExample.java

当运行JDBCExample，它会产生以下结果：

C:>java JDBCExample

Connecting to database...

Creating statement...

Executing stored procedure...

Emp Name with ID:102 is Zaid

Goodbye!

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