JDBC Statement對象實例
以下是利用以下三種查詢以及打開和關閉說明的例子：
boolean execute(String SQL) : 返回一個布爾值true，如果ResultSet對象可以被檢索，否則返回false。使用這個方法來執行SQL DDL語句，或當需要使用真正的動態SQL。
int executeUpdate(String SQL) : 返回受影響的SQL語句執行的行數。使用此方法來執行，而希望得到一些受影響的行的SQL語句 - 例如，INSERT，UPDATE或DELETE語句。
ResultSet executeQuery(String SQL) : 返回ResultSet對象。當希望得到一個結果集使用此方法，就像使用一個SELECT語句。
基于對環境和數據庫安裝在前面的章節中做此示例代碼已被寫入。
復制下面的例子中JDBCExample.java，編譯并運行，如下所示：
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//STEP 1. Import required packagesimport 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 |
現在編譯上面的例子如下：
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C:>javac JDBCExample.java |
當運行JDBCExample，它會產生以下結果：
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C:>java JDBCExample |
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Connecting to database...Creating statement...Return value is : falseRows impacted : 1ID: 100, Age: 18, First: Zara, Last: AliID: 101, Age: 25, First: Mahnaz, Last: FatmaID: 102, Age: 30, First: Zaid, Last: KhanID: 103, Age: 30, First: Sumit, Last: MittalGoodbye! |
JDBC CallableStatement對象實例
下面是利用CallableStatement連同下列getEmpName()的MySQL存儲過程的例子：
請確定已經在EMP數據庫中創建該存儲過程。可以使用MySQL查詢瀏覽器來完成它。
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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 ; |
基于對環境和數據庫安裝在前面的章節中進行，這個范例程式碼已被寫入。
復制下面的例子中JDBCExample.java，編譯并運行，如下所示：
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//STEP 1. Import required packagesimport 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 |
現在編譯上面的例子如下：
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C:>javac JDBCExample.java |
當運行JDBCExample，它會產生以下結果：
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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 ZaidGoodbye! |
