Java的JDBC中Statement與CallableStatement對象實例

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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!