JDBC PreparedStatement範例

以下是使用PreparedStatement以及開啟資料連線，執行SQL語句，然後關閉與資料庫連線的範例，這個範例中的程式碼是基於前面章節中完成的環境和資料庫設定編寫的。

複製以下程式碼儲存到JDBCPreparedStatement.java檔案中，編譯並執行如下 -

//STEP 1. Import required packages
// detail at /20/213/8320.html

import java.sql.*;

public class JDBCPreparedStatement {
   // 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 = "root";
   static final String PASS = "123456";

   public static void main(String[] args) {
   Connection conn = null;
   PreparedStatement 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 = "UPDATE Employees set age=? WHERE id=?";
      stmt = conn.prepareStatement(sql);

      //Bind values into the parameters.
      stmt.setInt(1, 35);  // This would set age
      stmt.setInt(2, 102); // This would set ID

      // Let us update age of the record with ID = 102;
      int rows = stmt.executeUpdate();
      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 JDBCPreparedStatement

現在編譯上面的例子如下 -

## 編譯 Java 程式碼
F:\worksp\jdbc>javac -Djava.ext.dirs=F:\worksp\jdbc\libs JDBCPreparedStatement.java
## 執行 Java 程式碼
F:\worksp\jdbc>java -Djava.ext.dirs=F:\worksp\jdbc\libs JDBCPreparedStatement

執行JDBCPreparedStatement時，應該會看到輸出以下結果 -