JDBC的链接及封装

Posted 2020-10-02 Lverson_tester

导入 mysql 的jar包

jar包：可以直接拿来用，又不想我们看到源代码

 

sql语句 一定注意：当update，delete时 一定注意where 条件，一定要写！！！

public static void add() {
            // try catch 捕获异常，try有异常会跳到catch
            Connection con = null;
            try {
                  // 1.选择要连接哪一种数据库---JDBC加载数据库驱动
                  Class.forName("com.mysql.jdbc.Driver");
                  // 2.创建链接（主机名，端口号，用户名，密码）---url包含主机名+端口号+数据库
                  con = DriverManager.getConnection("jdbc:mysql://localhost:3306/yyy", "root", "123456");
                  // 3.选择操作的数据库--此动作在上一步的url中集成
                  // 4.创建命令窗口 写 sql语句
                  PreparedStatement pstmt = con.prepareStatement("insert into zhuce (name,password,sex,id) value(?,?,?,?)");
                  pstmt.setString(1, "8888");
                  pstmt.setString(2, "8888");
                  pstmt.setString(3, "F");
                  pstmt.setString(4, "8888");
                  // 5.运行sql语句 ，查看结果---增删改调用executeUpdate 返回受影响的行数；查询调用 executeQuery
                  // 返回查询结果集
                  int result = pstmt.executeUpdate();
                  System.out.println(result);

            } catch (ClassNotFoundException e) {
                  // TODO Auto-generated catch block
                  e.printStackTrace();
            } catch (SQLException e) {
                  // TODO Auto-generated catch block
                  e.printStackTrace();
            } finally {
                  try {
                        if (con != null) {
                              con.close();
                        }
                  } catch (SQLException e) {
                        e.printStackTrace();
                  }
            }
      }
public static void main (String[] args){
                  add();
      }

以上是add方法，update和delete方法只是改变了sql语句

update://根据主键查询
PreparedStatement pstmt = con.prepareStatement("update zhuce set sex=?,id=? where name=? and password=?");
pstmt.setString(1, "M");
pstmt.setString(2, "2222");
pstmt.setString(3, "2222");
pstmt.setString(4, "1111");

delete://删除主键
PreparedStatement pstmt = con.prepareStatement("delete from zhuce where name=?and password=?");
pstmt.setString(1, "8888");
pstmt.setString(2, "8888");

 JDBC的封装

将1，2步  close  sql语句的输出 进行封装

public class JdbcUtil {
    public static Connection getConnection(){
      Connection con =null;
      try {
            //1.加载驱动
                  Class.forName("com.mysql.jdbc.Driver");
                  //2.创建连接
                  con=DriverManager.getConnection("jdbc:mysql://localhost:3306/yyy", "root", "123456");
            } catch (ClassNotFoundException e) {
                  // TODO Auto-generated catch block
                  e.printStackTrace();
            } catch (SQLException e) {
                  // TODO Auto-generated catch block
                  e.printStackTrace();
            }
      return con;
    }

    public static void close(Connection con){
      try {
            if(con!=null){
                      con.close();
            }
            } catch (SQLException e) {
                  // TODO Auto-generated catch block
                  e.printStackTrace();
            }
    }

    public static int executeUpdate(String sql,Object[] params){
      Connection con = getConnection();
      int result =0;
      try {
                  PreparedStatement pstmt = con.prepareStatement(sql);
                  if(params!=null){
                      for(int i=0;i<params.length;i++){
                        pstmt.setObject(i+1, params[i]);
                      }
                  }
                  result = pstmt.executeUpdate();
            } catch (SQLException e) {
                  // TODO Auto-generated catch block
                  e.printStackTrace();
            }finally {
                  close(con);
            }
      return result;
    }
}

JAVABEAN

又叫 bean 等

跟数据库里面的表发生映射

package com.neuedu.bean;

import com.sun.org.apache.xml.internal.security.Init;

public class Student {
    private Integer sid;
    private String sname;
    private Integer age;
    private Integer sex;
    //这四句代码就是javabean
      public Integer getSid() {
            return sid;
      }
      public void setSid(Integer sid) {
            this.sid = sid;
      }
      public String getSname() {
            return sname;
      }
      public void setSname(String sname) {
            this.sname = sname;
      }
      public Integer getAge() {
            return age;
      }
      public void setAge(Integer age) {
            this.age = age;
      }
      public Integer getSex() {
            return sex;
      }
      public void setSex(Integer sex) {
            this.sex = sex;
      }
      public Student(Integer sid, String sname, Integer age, Integer sex) {
            super();
            this.sid = sid;
            this.sname = sname;
            this.age = age;
            this.sex = sex;
      }
      public Student() {
            super();
            // TODO Auto-generated constructor stub
      }
      @Override
      public String toString() {
            return "Student [sid=" + sid + ", sname=" + sname + ", age=" + age + ", sex=" + sex + "]";
      }

}

简化

使用动态数组

//一个方法中只能有一个动态参数

//动态参数必须位于参数列表的最后一个

将之前object[] 改成 动态数组 object...

public static int executeUpdate(String sql,Object... params)

 增删改 方法简化

public static int update(Student student){
       return JdbcUtil.executeUpdate("update student set sname=?,age=?,sex=? where sid=?",student.getSname(),student.getAge(),student.getSex(),student.getSid());
      }

public static int  add(Student student) {
       return JdbcUtil.executeUpdate("insert into student (sid,sname,age,sex) values(?,?,?,?)", student.getSid(),student.getSname(),student.getAge(),student.getSex());
      }

public static int  delete(int id){
       return JdbcUtil.executeUpdate("delete from student where sid=?", id);
      }

 

查询不适合用数组，因为不知道有多少数据；用集合，集合有两种  ArrayList,LinkedList

基于ArrayList（Vector，ArrayList）适合查询，而LinkedList（链表）适合添加，删除操作。

用到 游标 的操作：rs.next() ，判断有没有下一行数据，有的话 游标推到下一行，并返回true ；反之 返回false 。 首先从最上面开始

第一次调用rs.next() 就会调用首行的下一行，也就是第一行数据

public static List<Student> getStudents(){
        Connection con = null;
        List<Student> list = new ArrayList<>();
        try {
             Class.forName("com.mysql.jdbc.Driver");
             con=DriverManager.getConnection("jdbc:mysql://localhost:3306/yyy", "root", "123456");
             PreparedStatement pstmt = con.prepareStatement("select * from student");
             ResultSet rs = pstmt.executeQuery();
             while(rs.next()){
                   Student student=new Student();
                   student.setSid(rs.getInt("sid"));
                   student.setSname(rs.getString("sname"));
                   student.setSname(rs.getString("age"));
                   student.setSname(rs.getString("sex"));
                   list.add(student);
             }
        } catch (ClassNotFoundException e) {
              // TODO Auto-generated catch block
              e.printStackTrace();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
               e.printStackTrace();
        }finally{
              try {
                    if(con!=null){
                          con.close();
                    }
              } catch (Exception e2) {
                    // TODO: handle exception
               }
        }
        return list;
   }
}

public static void main (String[] args){
    List<Student> students=getStudents();
    System.out.println(students);
}