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!