springboot2.0 整合mybatis 梳理

最终效果图

 

第一步:创建springboot开发模板,选择2.0,需要选择的jar包有web,jdbc,mysql

第二步:编写配置文件,我习惯使用yml格式来配置

server:
  port: 8081
spring:
  datasource:
    url: jdbc:mysql://localhost:3307/test
    username: root
    password: root
    driver-class-name: com.mysql.jdbc.Driver
mybatis:
  mapper-locations: classpath:mapper/*.xml

第三步:创建表

CREATE TABLE `student` (
  `id` int(11) DEFAULT NULL,
  `name` varchar(30) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `sex` varchar(20) DEFAULT NULL,
  `telephone` int(11) NOT NULL,
  `xueli` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`telephone`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

第四步:创建bean

package com.restart.bootlesson.bean;

public class Student {
    private int id;
    private String name;
    private int age;
    private String sex;
    private int telephone;
    private String xueli;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public int getTelephone() {
        return telephone;
    }

    public void setTelephone(int telephone) {
        this.telephone = telephone;
    }

    public String getXueli() {
        return xueli;
    }

    public void setXueli(String xueli) {
        this.xueli = xueli;
    }


}

第五步:创建mapper类

package com.restart.bootlesson.mapper;

import com.restart.bootlesson.bean.Student;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Select;

import java.util.List;
import java.util.Map;
@Mapper
public interface StudentMapper {
//    @Select("select * from student")
    public List<Student> query(Map<String,Object> param);
}

第六步:创建mapper.xml文件,在resource下先建立一个mapper文件夹

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.restart.bootlesson.mapper.StudentMapper">
    <resultMap type="com.restart.bootlesson.bean.Student" id="studentResult">
        <result property="id" column="id" jdbcType="INTEGER"/>
        <result property="name" column="name" jdbcType="VARCHAR"/>
        <result property="age" column="age" jdbcType="INTEGER"/>
        <result property="sex" column="sex" jdbcType="VARCHAR"/>
        <result property="telephone" column="telephone" jdbcType="INTEGER"/>
        <result property="xueli" column="xueli" jdbcType="VARCHAR"/>
    </resultMap>
    <select id="query" parameterType="java.util.Map" resultMap="studentResult" >
       SELECT * FROM student;
    </select>
</mapper>

第七步:创建service

package com.restart.bootlesson.service;

import com.restart.bootlesson.bean.Student;
import com.restart.bootlesson.mapper.StudentMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;
import java.util.Map;

@Service("studentService")
@Transactional
public class StudentService {
    @Autowired
    private StudentMapper studentMapper;

    public List<Student> query(Map<String, Object> param) {
        System.out.println("service");
        return studentMapper.query(param);
    }
}

第八步:创建controller

package com.restart.bootlesson.controller;

import com.restart.bootlesson.bean.Student;
import com.restart.bootlesson.mapper.StudentMapper;
import com.restart.bootlesson.service.StudentService;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.annotation.Resource;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

@RestController
public class StartController {

    @Resource
    private StudentService studentService;


    @RequestMapping("/hello")
    public String hello(){

        return "hello world";
    }

    @RequestMapping("/query")
    public String query(){
        Map<String, Object> param = new HashMap<>();
        param.put("id",1);

        List<Student> list = studentService.query(param);

        Student student = list.get(0);


        return student.getName()+"--"+student.getSex();


    }

}

第九步:启动,访问,页面输出结果:

C--男

在配置过程中出现过几个问题,我觉得需要记录一下:

1.

org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): com.restart.bootlesson.mapper.StudentMapper.query
    at org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(MapperMethod.java:225) ~[mybatis-3.4.5.jar:3.4.5]

关于这个异常,在网上着了 很多答案,但是各执一词,提供的方案也未必管用.

这个异常的原因是在访问时,没有找到mapper对应的配置文件.之所以会出现这个问题,是因为在最开始配置时,是因为没有指定mybatis相关配置.

有二种解决方案:

第一种就是按照我现在的配置:对mybatis进行指定要扫描的位置

server:
  port: 8081
spring:
  datasource:
    url: jdbc:mysql://localhost:3307/test
    username: root
    password: root
    driver-class-name: com.mysql.jdbc.Driver
mybatis:
  mapper-locations: classpath:mapper/*.xml

一开始我并没有配置这个,所以报找不到对应的方法这个异常.

第二种解决方案是添加mybatis-config.xml,在这个配置文件中指定每个mapper类映射的配置文件,这个方案我没有验证,因为这种解决思路其实和上面的殊途同归.

网上还有一种更改pom.xml文件的做法,在里边配置

<build>
 <resources>
  <resource>
   <directory>src/main/java</directory>
   <includes>
        <include>**/*.xml</include>
   </includes>
  </resource>
  <resource>
   <directory>src/main/resources</directory>
  </resource>
 </resources>
</build>

这种做法是用来解决maven在编译时不把xml文件编译到class中这种情况的,后来经过验证,如果按照方案1的配置,即便pom.xml不配置这些,也仍然能够跑通.

2.

Error starting ApplicationContext. To display the auto-configuration report re-run your application with 'debug' enabled.
2018-03-11 12:48:21.317 ERROR 453992 --- [           main] o.s.b.d.LoggingFailureAnalysisReporter   : 

***************************
APPLICATION FAILED TO START
***************************

Description:

Field studentMapper in com.restart.bootlesson.service.StudentService required a bean of type 'com.restart.bootlesson.mapper.StudentMapper' that could not be found.


Action:

Consider defining a bean of type 'com.restart.bootlesson.mapper.StudentMapper' in your configuration.

这个错误的原因是我一开始虽然自动注入了mapper,但是spring没有获取到这个bean,由于没找到,所以无法启动.

两个解决方案:

第一种:@Mapper

@Mapper
public interface StudentMapper {
//    @Select("select * from student")
    public List<Student> query(Map<String,Object> param);
}

在这个mapper类上边添加@mapper注解,就是告诉spring这个类是一个mapper

第二种:@MapperScan

@SpringBootApplication
@MapperScan("com.restart.bootlesson.mapper")
public class BootLessonApplication {

    public static void main(String[] args) {
        SpringApplication.run(BootLessonApplication.class, args);
    }
}

在启动类上添加这个注解,并制定要扫描的mapper类所在位置,作用和@Mapper是一样的.

特别注意的是,springboot对目录层级是有要求的.启动类必须在所有controller,service,mapper所在目录的最外顶层.spring会按照启动类所在包位置逐级扫描.