摘要：知識點總結連接步驟及知識點總結連接數據庫步驟依序關閉使用的對象連接操作加載對應驅動建立連接連接對象內部包含了對象，是一個遠程連接。比較耗時這是對象管理的一個要點真正開發中，為了提高效率，都會使用連接池來管理連接對象張柏芝女張三執行結果

@(Java知識點總結)[Java, JDBC]

依序關閉使用的對象連接：

ResultSet -> Statement -> Connection

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
 
 
public class StudentDao {
 
  private static Connection getConn() {
      String driver = "com.mysql.jdbc.Driver";
      String url = "jdbc:mysql://localhost:3306/test";
      String username = "root";
      String password = "123";
      Connection conn = null;
      try {
          Class.forName(driver); //classLoader,加載對應驅動
          //建立連接（連接對象內部包含了Socket對象，是一個遠程連接。比較耗時！這是Connection對象管理的一個要點！）
          //真正開發中，為了提高效率，都會使用連接池來管理連接對象！
          conn = (Connection) DriverManager.getConnection(url, username, password);
      } catch (ClassNotFoundException e) {
          e.printStackTrace();
      } catch (SQLException e) {
          e.printStackTrace();
      }
      return conn;
  }
  
  private static int insert(User user) {
      Connection conn = getConn();
      int i = 0;
      String sql = "insert into users (Name,Sex,Age) values(?,?,?)";
      PreparedStatement pstmt = null;
      try {
          pstmt = (PreparedStatement) conn.prepareStatement(sql);
          pstmt.setString(1, user.getName());
          pstmt.setString(2, user.getSex());
          pstmt.setInt(3, user.getAge());
          i = pstmt.executeUpdate();
          pstmt.close();
          conn.close();
      } catch (SQLException e) {
          e.printStackTrace();
      }finally {
     try {
      pstmt.close();
     } catch (SQLException e) {
      e.printStackTrace();
     }
     try {
      conn.close();
     } catch (SQLException e) {
      e.printStackTrace();
     }
   }
      return i;
  }
  
  private static int update(User user) {
      Connection conn = getConn();
      int i = 0;
      String sql = "update users set Age="" + user.getAge() + "" where Name="" + user.getName() + """;
      PreparedStatement pstmt = null;
      try {
          pstmt = (PreparedStatement) conn.prepareStatement(sql);
          i = pstmt.executeUpdate();
          System.out.println("resutl: " + i);
          pstmt.close();
          conn.close();
      } catch (SQLException e) {
          e.printStackTrace();
      }finally {
     try {
      pstmt.close();
     } catch (SQLException e) {
      e.printStackTrace();
     }
     try {
      conn.close();
     } catch (SQLException e) {
      e.printStackTrace();
     }
   }
      return i;
  }
  
  private static Integer getAll() {
      Connection conn = getConn();
      String sql = "select * from users";
      PreparedStatement pstmt =null;
      ResultSet  rs = null;
      try {
          pstmt = (PreparedStatement)conn.prepareStatement(sql);
          rs = pstmt.executeQuery();
          int col = rs.getMetaData().getColumnCount();
          System.out.println("============================");
          while (rs.next()) {
              for (int i = 1; i <= col; i++) {
                  System.out.print(rs.getString(i) + "	");
                  if ((i == 2) && (rs.getString(i).length() < 8)) {
                      System.out.print("	");
                  }
               }
              System.out.println("");
          }
              System.out.println("============================");
      } catch (SQLException e) {
          e.printStackTrace();
      }finally {
       try {
      rs.close();
     } catch (SQLException e1) {
      e1.printStackTrace();
     }
     try {
      pstmt.close();
     } catch (SQLException e) {
      e.printStackTrace();
     }
     try {
      conn.close();
     } catch (SQLException e) {
      e.printStackTrace();
     }
   }
      return null;
  }
  
  private static int delete(String name) {
      Connection conn = getConn();
      int i = 0;
      String sql = "delete from users where Name="" + name + """;
      PreparedStatement pstmt = null;
      try {
          pstmt = (PreparedStatement) conn.prepareStatement(sql);
          i = pstmt.executeUpdate();
          System.out.println("resutl: " + i);
          pstmt.close();
          conn.close();
      } catch (SQLException e) {
          e.printStackTrace();
      }finally {
     try {
      pstmt.close();
     } catch (SQLException e) {
      e.printStackTrace();
     }
     try {
      conn.close();
     } catch (SQLException e) {
      e.printStackTrace();
     }
   }
      return i;
  }
  
  public static void main(String[] args) {
   getAll();
       insert(new User("張柏芝", "女", 43));
       getAll();
       update(new User("張三", "", 38));
       delete("Achilles");
       getAll();
  }
}

public class User {
 
  private int id;
  private int age;
  private String name ;
  private String sex;
  
  
  public User( String name, String sex,int age) {
   this();
   this.age = age;
   this.name = name;
   this.sex = sex;
  }
  public User() {
 
  }
  public int getAge() {
   return age;
  }
  public int getId() {
   return id;
  }
  public String getName() {
   return name;
  }
  public String getSex() {
   return sex;
  }
  public void setAge(int age) {
   this.age = age;
  }
  public void setId(int id) {
   this.id = id;
  }
  public void setName(String name) {
   this.name = name;
  }
  public void setSex(String sex) {
   this.sex = sex;
  }
  
}

執行結果：