Java知识点总结（JDBC-连接步骤及CRUD）

摘要：知识点总结连接步骤及知识点总结连接数据库步骤依序关闭使用的对象连接操作加载对应驱动建立连接连接对象内部包含了对象，是一个远程连接。比较耗时这是对象管理的一个要点真正开发中，为了提高效率，都会使用连接池来管理连接对象张柏芝女张三执行结果

@(Java知识点总结)[Java, JDBC]

依序关闭使用的对象连接：

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,加载对应驱动
          //建立连接（连接对象内部包含了Socket对象，是一个远程连接。比较耗时！这是Connection对象管理的一个要点！）
          //真正开发中，为了提高效率，都会使用连接池来管理连接对象！
          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("张柏芝", "女", 43));
       getAll();
       update(new User("张三", "", 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;
  }
  
}

执行结果：