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() );

// Let 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!