Java使用c3p0连接池完成多表级联查询

Posted 2021-04-06 源码客栈

引言：今天讲述实现一对一多表查询，完成两个表的关联，查询出两张表的所有字段信息。

准备工作：idea开发工具，可以在maven仓库下载c3p0连接池的jar包，对一对一，一对多有所了解，对多表查询的sql语句要有所了解，需要一定的Java基础。

1.建表

首先两张表要建立一定的关联，即一张表的主键作为另一张表的外键，本次我们有学生表和用户表，属于一对一的关系，我们就以学生表为主表，也就是他的主键当作用户表的外键

---

admin表，它的外键参考的是student表的主键

sutent作为主表，一对一的左侧，当然两张表调换也是可以

这个设置在admin表的外键序列里，我们参考的学生表的主键id，更新和删除设置restrict.具体的区别可以百度一下。

2.配置c3p0连接池

<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
   <default-config>
 <property name="driverClass">com.mysql.jdbc.Driver
</property>
 <property name="jdbcUrl">jdbc:mysql://localhost:3306/
db_student_system?useUnicode=true&amp;
characterEncoding=utf-8</property>
      <property name="user">root</property>
      <property name="password">123456</property>
      <property name="acquireIncrement">5</property>
      <property name="initialPoolSize">10</property>
      <property name="minPoolSize">5</property>
      <property name="maxPoolSize">20</property>
   </default-config>
</c3p0-config>

3.获取链接

package utils;
import java.sql.Connection;
import java.sql.SQLException;
import javax.sql.DataSource;
import com.mchange.v2.c3p0.ComboPooledDataSource;
public class C3p0Utils {
   private static DataSource ds;
   static{
      ds=new ComboPooledDataSource();
   }
   public static DataSource getDs(){
      return ds;
   }
public static Connection getConnection() throws
SQLException{
return ds.getConnection();
   }
public static void main(String args[])
throws SQLException {
 System.out.println(new C3p0Utils()
.getConnection()+"mysql is ok");
   }
}

4.建数据模型层

public class Student {
    private int id;
    private String stuno;
    private String sclass;
 private String sex;
    private Admin admin;
 public Student( int id,String stuno, String sclass,
 String sex,String political, String sname, Integer age,
 String level, String phone, String qq) {
        this.id=id;
        this.stuno = stuno;
        this.sclass = sclass;
        this.sex = sex;

        this.political = political;
        this.sname = sname;
        this.age = age;
        this.level = level;
        this.phone = phone;
        this.qq = qq;
    }
public Student(Integer id, String stuno,
String sclass, String sex, String account,
String pwd,String type, String political, String sname, Integer age, String level, String phone, String qq) {
super();
        this.id = id;
        this.stuno = stuno;
        this.sclass = sclass;
        this.sex = sex;
        this.admin=new Admin(account,pwd,type);
        this.political = political;
        this.sname = sname;
        this.age = age;
        this.level = level;
        this.phone = phone;
        this.qq = qq;
 }
     private String political;
    private String sname;
    private Integer age;
    private String level;
    private String phone;
    private String qq;

    public Student(Admin admin) {this.admin = admin;}
    public Admin getAdmin() {return admin;}
    public void setAdmin(Admin admin) {this.admin = admin;}
  ***********各个属性的setter和getter方法**********
}
******这个是admin表的**
package model;/*
public class Admin {
    private Integer id;
    private String account;
    private String pwd;
 private String type;
    private int s_id;

    public void setAccount(String account) { this.account = account;}
    public Admin() {}
 //构造方法，初始化对象
public Admin(String account, String pwd, String type) {
        this.account = account;
        this.pwd = pwd;
        this.type = type;
    }
    public Admin(String account, String pwd, String type, int s_id) {
        this.account = account;
        this.pwd = pwd;
        this.type = type;
        this.s_id = s_id;
    }
 ***********各个属性的setter和getter方法**********
}

5.建立dao层

import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import model.Student;
import org.apache.commons.dbutils.handlers.MapListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;
import utils.C3p0Utils;
public class StudentDao {
//获取连接执行查询
private QueryRunner runner=new QueryRunner(C3p0Utils.getDs()
);

public List<Map<String,Object>> findAll() {
   List<Map<String,Object>> list=null;
   try {
 String sql = "select s.*,a.* from student s left join
 admin a on s.id=a.s_id ";//左连接查询，查询的是两张表关联的字段。
      //创建一个集合用来存储查询的参数，因为我们不清楚客户到底输入几个参数，所以用集合来存放
 list=runner.query(sql, new MapListHandler());
   } catch (SQLException e) {//捕获异常
 throw new RuntimeException(e);//抛出运行异常
 }
   return list;
}

public static void main(String[] args){
   StudentDao dao=new StudentDao();//调用对象
 List<Map<String,Object>> list=dao.findAll();//把多表两张表
查询的字段封装到Map里，再封装到List集合里。
 Iterator<Map<String,Object>> iterator=list.iterator();
//使用迭代器遍历集合。
   while (iterator.hasNext()){
      System.out.println(iterator.next());
   }
}

}

6.运行结果截图

7.演示视频。