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:
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//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:
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C:>javac JDBCExample.java |
当运行JDBCExample,它会产生以下结果:
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C:>java JDBCExample |
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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。
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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:
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//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:
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C:>javac JDBCExample.java |
当运行JDBCExample,它会产生以下结果:
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C:>java JDBCExample |
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Connecting to database... Creating statement... Executing stored procedure... Emp Name with ID:102 is Zaid Goodbye! |