spring-boot+mybatis搭建一个后端restfull服务

1、创建一个maven项目。

2、在pom.xml中引入依赖包，如下所示：

    4.0.0

    com.best
    spring-boot-mybatis
    1.0-SNAPSHOT

    
        1.8
        1.2.74
        5.3.5.RELEASE
        UTF-8
        UTF-8
    
    
        org.springframework.boot
        spring-boot-starter-parent
        2.3.5.RELEASE
    
    
        
            org.springframework.boot
            spring-boot-starter-web
        
        
            org.springframework.boot
            spring-boot-starter-test
            test
        
        
            org.springframework.boot
            spring-boot-starter-jdbc
            
                
                
                    org.apache.tomcat
                    tomcat-jdbc
                
            
        
        
        
        
        
        
            org.mybatis.spring.boot
            mybatis-spring-boot-starter
            2.1.3
        
        
            mysql
            mysql-connector-java
            8.0.22
        
        
            com.alibaba
            druid
            1.2.1
        
        
            com.alibaba
            fastjson
            ${fastjson.version}
        
        
            org.projectlombok
            lombok
            1.18.10
        
        
            org.mybatis.spring.boot
            mybatis-spring-boot-starter
            2.1.3
        
    
    
        
            
                org.apache.maven.plugins
                maven-compiler-plugin
                3.8.0
                
                    1.8
                    1.8
                
            
        
    

3、在使用mybatis之前，那么首先需要创建数据表，如：

DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) COLLATE utf8_bin DEFAULT NULL,
  `create_date` datetime DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES ('1', 'user1', '2020-11-10 21:01:54');
INSERT INTO `user` VALUES ('2', 'user2', '2020-11-01 21:02:12');

4、然后配置数据库连接池，这里使用的是alibaba的druid，首先在resources中新建一个application.yml文件，内容如下：

spring:
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    driver-class-name: com.mysql.cj.jdbc.Driver
    platform: mysql
    url: jdbc:mysql://localhost:3306/springboottest?useUnicode=true&characterEncoding=UTF-8&useSSL=false&serverTimezone=CTT
    username: root
    password:
server:
  port: 8080

5、然后新建一个包com.best.db，并新建一个DruidDBConfig类，代码如下：

package com.best.db;

import com.alibaba.druid.pool.DruidDataSource;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.SqlSessionFactoryBean;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.jdbc.datasource.DataSourceTransactionManager;

import javax.sql.DataSource;

/**
 * @author:sunxj
 * @date:2020-11-10 21:08:53
 * @description: 数据连接池
 */
@Configuration
public class DruidDBConfig {
    @Value("${spring.datasource.url}")
    private String url;
    @Value("${spring.datasource.username}")
    private String username;
    @Value("${spring.datasource.password}")
    private String password;
    @Value("${spring.datasource.driver-class-name}")
    private String driverClassName;
    @Bean//DataSource 对象为 Spring 容器所管理;
    @Primary//表示这里定义的DataSource将覆盖其他来源的DataSource。
    public DataSource dataSource(){
        DruidDataSource datasource = new DruidDataSource();
        datasource.setUrl(this.url);
        datasource.setUsername(username);
        datasource.setPassword(password);
        datasource.setDriverClassName(driverClassName);
        return datasource;
    }
    //配置数据库事务
    @Bean(name = "transactionManager")
    public DataSourceTransactionManager dbOneTransactionManager(
            @Qualifier("dataSource") DataSource dataSource) {
        return new DataSourceTransactionManager(dataSource);
    }
    //配置数据库工厂
    @Bean(name = "sqlSessionFactory")
    @ConditionalOnMissingBean(name = "sqlSessionFactory")
    public SqlSessionFactory dbOneSqlSessionFactory(@Qualifier("dataSource") DataSource dataSource) throws Exception {
        final SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
        sessionFactory.setDataSource(dataSource);
        return sessionFactory.getObject();
    }
}

6、配置好连接池，那么就可以开始配置entity了，也就是与表映射的实体类，这里我们使用lombok的注解自动生成set和get方法，那么新建一个com.best.entity包，并新建一个User类，如：

package com.best.entity;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import java.util.Date;

/**
 * @author:sunxj
 * @date:2020-11-10 21:12:58
 * @description:用户实体类
 */
@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private Integer id;
    private String name;
    private Date createDate;
}

7、实体类创建好了之后，那么就是创建mybatis映射文件以及类了，这里的映射接口文件和Mapper.xml文件放到一起，首先创建一个com.best.dbo包，映射接口文件和.xml都放到这个包中，并创建一个接口UserMapper，如：

package com.best.dao;

import com.best.entity.User;
import org.springframework.stereotype.Repository;

import java.util.List;
/**
 * @author:sunxj
 * @date:2020-11-10 21:17:27
 * @description:用户表的映射接口文件
 */
@Repository
public interface UserMapper {
    List selectAll();
    User selectById(Integer id);
}

8、配置Mapper映射的xml文件，文件名为UserMapper.xml：

    
        
        
        
    
    
        SELECT * FROM user
    
    
        SELECT * FROM user WHERE id=#{id}
    

9、在配置好之后就可以在application.xml来指定mybatis扫描哪些映射文件，配置如下：

spring:
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    driver-class-name: com.mysql.cj.jdbc.Driver
    platform: mysql
    url: jdbc:mysql://localhost:3306/springboottest?useUnicode=true&characterEncoding=UTF-8&useSSL=false&serverTimezone=CTT
    username: root
    password:
mybatis:
  #如果有多个目录则可以写多个，比如com/best/dao/*.xml，com/best/*/dao/*.xml,com/best/*/sss/*/dao/*.xml
  mapper-locations: classpath:com/best/dao/*.xml
  #配置包，这里同样可以配置多个，
  type-aliases-package: com.best.dao
server:
  port: 8080

注意：如果是将mapper.xml和java文件放到一个目录中，也就是src目录中，那么必须在pom中加入如下语句：

    
        
            
                src/main/java
                
                    **/*.xml
                
            
        
    

10、配置好之后就开始配置service以及impl了，首先创建一个service和service/impl包，并在service下创建一个IUserService接口，并在impl下来实现该接口UserServiceImpl，代码如下：

package com.best.service;

import com.best.entity.User;
import java.util.List;
/**
 * @author:sunxj
 * @date:2020-11-10 21:33:23
 * @description:用户接口表
 */
public interface IUserService {
    List selectAll();
    User selectById(Integer id);
}

package com.best.service.impl;

import com.best.dao.UserMapper;
import com.best.entity.User;
import com.best.service.IUserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

/**
 * @author:sunxj
 * @date:2020-11-10 21:34:34
 * @description:用户接口实现类
 */
@Service("userService")
public class UserServiceImpl implements IUserService {
    @Autowired
    private UserMapper userMapper;
    @Override
    public List selectAll() {
        return userMapper.selectAll();
    }

    @Override
    public User selectById(Integer id) {
        return userMapper.selectById(id);
    }
}

11、在创建好service后，需要创建一个controller，如UserController，代码如下：

package com.best.controller;

import com.alibaba.fastjson.JSONObject;
import com.best.service.IUserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * @author:sunxj
 * @date:2020-11-10 21:38:09
 * @description:
 */
@RestController//使用此注解，那么该类下的所有返回都是以json方式返回
@RequestMapping(value="best")//加上value后，在url访问时必须加上/best才行
public class UserController {
    @Autowired
    private IUserService userService;
    @RequestMapping("/getUser")
    public JSONObject getUser(HttpServletRequest request, HttpServletResponse response) {
        JSONObject obj =  new JSONObject();
        obj.put("user","1111");
        return obj;
    }
}

12、创建好之后，最后创建一个spring-boot的入口文件，代码如下：

package com.best;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

/**
 * @author:sunxj
 * @date:2020-11-10 21:46:43
 * @description:
 */
@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class,args);
    }
}

13、此时启动会提示无法找到com.best.dao.UserMapper，如：

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2020-11-10 21:48:21.635 ERROR 10320 --- [           main] o.s.b.d.LoggingFailureAnalysisReporter   : 

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

Description:

Field userMapper in com.best.service.impl.UserServiceImpl required a bean of type 'com.best.dao.UserMapper' that could not be found.

The injection point has the following annotations:
	- @org.springframework.beans.factory.annotation.Autowired(required=true)


Action:

Consider defining a bean of type 'com.best.dao.UserMapper' in your configuration.

14、出现此问题是由于springboot在启动时，在UserServiceImpl中又使用到了UserMapper的自动注入，而springboot启动时就没有扫描到UserMapper，更不可能将它作为bean注入到IOC容器中，因此就无法注入了，那么需要再入口的main文件上加上@MapperScan即可，如：

package com.best;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

/**
 * @author:sunxj
 * @date:2020-11-10 21:46:43
 * @description:
 */
@SpringBootApplication
@MapperScan({"com.best.dao"})//如果有多个可以使用{"com.best.dao","com.best.sss.dao"}
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class,args);
    }
}

15、此时即可正常启动，如下图所示：

16、此时在浏览器中输入：http://localhost:8080/best/getUser即可，如下图所示：

17、以上只是搭建一个可以正常通过url访问，那么现在来访问数据库中的记录，在访问之前先创建一些封装类，比如将实体类封装成json、返回状态码等，先创建一个common包，在该包下创建entity、enums、utils等包，如下图所示：

18、然后在enums中创建一个ResultCode枚举类，此来定义了一些返回状态码信息，如下代码所示：

package com.best.common.enums;

/**
 * @author:sunxj
 * @date:2020-11-10 22:08:11
 * @description:返回码定义
 */
public enum ResultCode {
    //成功
    SUCCESS(200,"成功"),
    //默认失败
    COMMON_FAIL(404,"失败"),
    ;
    private Integer code;
    private String message;

    ResultCode(Integer code, String message) {
        this.code = code;
        this.message = message;
    }

    public Integer getCode() {
        return code;
    }

    public void setCode(Integer code) {
        this.code = code;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

    public static String getMessageByCode(Integer code) {
        for (ResultCode ele : values()) { //values会默认取出enum中的值对象列表，每个值都是一个ResultCode对象
            if (ele.getCode().equals(code)) {
                return ele.getMessage();
            }
        }
        return null;
    }
}

19、然后在entity中新建一个JsonResult类，用来封装统一返回的实体类，如：

package com.best.common.entity;

import com.best.common.enums.ResultCode;

import java.io.Serializable;

/**
 * @author:sunxj
 * @date:2020-11-10 22:06:50
 * @description:统一返回的实体类
 */
public class JsonResult implements Serializable {
    private Boolean success;
    private Integer errorCode;
    private String errorMsg;
    private T data;

    public JsonResult() {
    }

    public JsonResult(Boolean success) {
        this.success = success;
        this.errorCode = success ? ResultCode.SUCCESS.getCode():ResultCode.COMMON_FAIL.getCode();
        this.errorMsg = success ? ResultCode.SUCCESS.getMessage():ResultCode.COMMON_FAIL.getMessage();
    }
    public JsonResult(Boolean success,ResultCode resultCode) {
        this.success = success;
        this.errorCode = success ? ResultCode.SUCCESS.getCode():(resultCode == null ? ResultCode.COMMON_FAIL.getCode():resultCode.getCode());
        this.errorMsg = success ? ResultCode.SUCCESS.getMessage():(resultCode == null ? ResultCode.COMMON_FAIL.getMessage():resultCode.getMessage());
    }
    public JsonResult(Boolean success,T data) {
        this.success = success;
        this.errorCode = success ? ResultCode.SUCCESS.getCode():ResultCode.COMMON_FAIL.getCode();
        this.errorMsg = success ? ResultCode.SUCCESS.getMessage() : ResultCode.COMMON_FAIL.getMessage();
        this.data = data;
    }
    public JsonResult(Boolean success,ResultCode resultCode,T data) {
        this.success = success;
        this.errorCode = success ? ResultCode.SUCCESS.getCode():(resultCode == null ? ResultCode.COMMON_FAIL.getCode():resultCode.getCode());
        this.errorMsg = success ? ResultCode.SUCCESS.getMessage():(resultCode == null ? ResultCode.COMMON_FAIL.getMessage():resultCode.getMessage());
        this.data = data;
    }

    public Boolean getSuccess() {
        return success;
    }

    public void setSuccess(Boolean success) {
        this.success = success;
    }

    public Integer getErrorCode() {
        return errorCode;
    }

    public void setErrorCode(Integer errorCode) {
        this.errorCode = errorCode;
    }

    public String getErrorMsg() {
        return errorMsg;
    }

    public void setErrorMsg(String errorMsg) {
        this.errorMsg = errorMsg;
    }

    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }
}

20、然后在utils中新建一个ResultTool，如下代码所示：

package com.best.common.utils;

import com.best.common.entity.JsonResult;
import com.best.common.enums.ResultCode;

/**
 * @author:sunxj
 * @date:2020-11-10 22:11:03
 * @description:json返回构造工具
 */
public class ResultTool {
    public static JsonResult success() {
        return new JsonResult(true);
    }
    public static  JsonResult success(T data) {
        return new JsonResult<>(true,data);
    }
    public static JsonResult fail() {
        return new JsonResult(false);
    }
    public static JsonResult fail(ResultCode resultCode) {
        return new JsonResult(false,resultCode);
    }
}

21、创建好这些之后，那么就可以开始在controller中进行构造了，controller如下：

package com.best.controller;

import com.best.common.entity.JsonResult;
import com.best.common.utils.ResultTool;
import com.best.entity.User;
import com.best.service.IUserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.List;

/**
 * @author:sunxj
 * @date:2020-11-10 21:38:09
 * @description:
 */
@RestController//使用此注解，那么该类下的所有返回都是以json方式返回
@RequestMapping(value="best")//加上value后，在url访问时必须加上/best才行
public class UserController {
    @Autowired
    private IUserService userService;
    @RequestMapping("/getUser")
    public JsonResult getUser(HttpServletRequest request, HttpServletResponse response) {
        List users = userService.selectAll();
        return ResultTool.success(users);
    }
}

22、重新启动springboot，然后输入：http://localhost:8080/best/getUser，此时页面会出现如下错误：

23、后台显示如下错误：

2020-11-10 22:15:10.487 ERROR 12992 --- [nio-8080-exec-4] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): com.best.dao.UserMapper.selectAll] with root cause

org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): com.best.dao.UserMapper.selectAll
	at org.apache.ibatis.binding.MapperMethod$SqlCommand.(MapperMethod.java:235) ~[mybatis-3.5.5.jar:3.5.5]
	at org.apache.ibatis.binding.MapperMethod.(MapperMethod.java:53) ~[mybatis-3.5.5.jar:3.5.5]
	at org.apache.ibatis.binding.MapperProxy.lambda$cachedInvoker$0(MapperProxy.java:115) ~[mybatis-3.5.5.jar:3.5.5]
	at java.util.concurrent.ConcurrentHashMap.computeIfAbsent(ConcurrentHashMap.java:1660) ~[na:1.8.0_261]
	at org.apache.ibatis.binding.MapperProxy.cachedInvoker(MapperProxy.java:102) ~[mybatis-3.5.5.jar:3.5.5]
	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:85) ~[mybatis-3.5.5.jar:3.5.5]
	at com.sun.proxy.$Proxy57.selectAll(Unknown Source) ~[na:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_261]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_261]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_261]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_261]
	at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:344) ~[spring-aop-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:198) ~[spring-aop-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.dao.support.PersistenceExceptionTranslationInterceptor.invoke(PersistenceExceptionTranslationInterceptor.java:139) ~[spring-tx-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) ~[spring-aop-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at com.sun.proxy.$Proxy58.selectAll(Unknown Source) ~[na:na]
	at com.best.service.impl.UserServiceImpl.selectAll(UserServiceImpl.java:22) ~[classes/:na]
	at com.best.controller.UserController.getUser(UserController.java:26) ~[classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_261]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_261]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_261]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_261]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) ~[spring-web-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) ~[spring-web-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105) ~[spring-webmvc-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:878) ~[spring-webmvc-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:792) ~[spring-webmvc-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) ~[spring-webmvc-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) ~[spring-webmvc-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) ~[spring-webmvc-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:626) ~[tomcat-embed-core-9.0.39.jar:4.0.FR]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) ~[tomcat-embed-core-9.0.39.jar:4.0.FR]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.39.jar:9.0.39]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) ~[spring-web-5.2.10.RELEASE.jar:5.2.10.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) ~[tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.core.StandardContextValve.__invoke(StandardContextValve.java:97) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:41002) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_261]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_261]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.39.jar:9.0.39]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_261]

23、这意思就是没有找到UserMapper接口文件中的selectAll方法，也就是没有和*Mapper.xml匹配成功，这是由于我们将.xml文件和java文件放在了java目录，而通过maven来管理，它不会将java文件中的xml文件打包进去的，因此需要再pom中的build中指定，如：

        
            
                src/main/java
                
                    **/dao/*Mapper.xml
                
            
         

24、然后在此重新运行，重新输入网址即可，如下图所示：

25、到此即可搭建完毕，使用此方法可以搭建一个前后端完全分离通过json通信的springboot后台。