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JDBC Statement對象實例
以下是應用以下三種查詢和翻開和封閉解釋的例子:
boolean execute(String SQL) : 前往一個布爾值true,假如ResultSet對象可以被檢索,不然前往false。應用這個辦法來履行SQL DDL語句,或當須要應用真實的靜態SQL。
int executeUpdate(String SQL) : 前往受影響的SQL語句履行的行數。應用此辦法來履行,而願望獲得一些受影響的行的SQL語句 - 例如,INSERT,UPDATE或DELETE語句。
ResultSet executeQuery(String SQL) : 前往ResultSet對象。當願望獲得一個成果集應用此辦法,就像應用一個SELECT語句。
基於對情況和數據庫裝置在後面的章節中做此示例代碼已被寫入。
復制上面的例子中JDBCExample.java,編譯並運轉,以下所示:
//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
如今編譯下面的例子以下:
C:>javac JDBCExample.java
當運轉JDBCExample,它會發生以下成果:
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對象實例
上面是應用CallableStatement連同以下getEmpName()的MySQL存儲進程的例子:
請肯定曾經在EMP數據庫中創立該存儲進程。可使用MySQL查詢閱讀器來完成它。
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 ;
基於對情況和數據庫裝置在後面的章節中停止,這個典范程式碼已被寫入。
復制上面的例子中JDBCExample.java,編譯並運轉,以下所示:
//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
如今編譯下面的例子以下:
C:>javac JDBCExample.java
當運轉JDBCExample,它會發生以下成果:
C:>java JDBCExample
Connecting to database... Creating statement... Executing stored procedure... Emp Name with ID:102 is Zaid Goodbye!