使用AOP+反射实现自定义Mybatis多表关联查询_Java教程

一、需求

目前使用的ORM框架是Mybatis Plus，是Mybatis的增强框架，基础的CRUD的方法都集成了，开发起来很是方便。但是项目中总是需要多表关联查询。

Mybatis的多表关联有两种

一、在Mapper中使用@Result @One @Many注解

二、在xml文件中配置对应的resultMap和关联标签

使用起来很不方便。JPA倒是有多表关联的注解实现，但是不想再引入另一个ORM框架。

目前的需求是增强现有的查询，使用简单的注解即可实现多表关联。

二、核心代码

GitHub：https://github.com/sushengbuyu/mybatis-mapping-demo

实现该功能总共需要四个文件

使用AOP+反射实现自定义Mybatis多表关联查询

两个自定义注解，一个虚拟Mapper，一个切面处理类

源码

MapTo

自定义映射注解，标注需要映射处理的字段

import java.lang.annotation.*;
/**
* @author victor
* @desc 自定义多表关联映射注解
* @date 2022/5/23
*/
@Documented
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface MapTo {
  /**
   * 映射目标
   */
  Class<?> targetClass();

  /**
   * 执行SQL
   */
  String sql();

  /**
   * 嵌套处理
   * 为true时，如果映射的对象类中有映射字段，也执行映射操作
   */
  boolean doDeep() default false;
}

DoMap

自定义映射处理注解，标注需要执行映射的方法

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* @author victor
* @desc 标注该需要执行映射处理的方法
* @date 2022/5/23
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface DoMap {
  /**
   * 需要处理映射的类
   * @return Class
   */
  Class<?> targetClass();

  /**
   * spel表达式
   * 默认为空
   * @return String
   */
  String spel() default "";
}

IDualMapper

虚拟Mapper，用来执行自定义SQL

import java.util.List;
import java.util.Map;
/**
* @author victor
* @desc 虚拟Mapper
* @date 2022/5/23
*/
@Mapper
public interface IDualMapper {

  /**
   * 执行自定义SQL
   * @param sql sql
   * @return List<Map<String, Object>>
   */
  List<Map<String, Object>> executeSql(String sql);
}

DualMapper

使用者自行实现DualMapper，解除mybatis强依赖

package sushengbuyu.maptodemo.sys.mapper;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import sushengbuyu.maptodemo.aop.IDualMapper;
import java.util.List;
import java.util.Map;
/**
* @author victor
* @desc 虚拟Mapper
* @date 2022/5/23
*/
@Mapper
public interface DualMapper extends IDualMapper {
  /**
   * 执行自定义SQL
   * @param sql sql
   * @return List<Map<String, Object>>
   */
  @Select("${sql}")
  List<Map<String, Object>> executeSql(@Param("sql") String sql);
}

DoMapAspect

切面处理类，核心代码，执行映射操作

package sushengbuyu.maptodemo.aop;
import cn.hutool.core.bean.BeanUtil;
import cn.hutool.core.util.ClassUtil;
import cn.hutool.core.util.ReUtil;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.expression.Expression;
import org.springframework.expression.ExpressionParser;
import org.springframework.expression.spel.standard.SpelExpressionParser;
import org.springframework.stereotype.Component;
import org.springframework.util.StringUtils;
import javax.annotation.PostConstruct;
import java.lang.reflect.Field;
import java.util.*;
import java.util.stream.Collectors;
/**
* @author victor
* @desc 自定义关联映射切面
* @date 2022/5/23
*/
@Component
@Aspect
public class DoMapAspect {
  private final static Logger log = LoggerFactory.getLogger(DoMapAspect.class);
  /**
   * 保存MapTo映射关系
   * key 映射字段所在类
   * value 映射字段集合
   */
  private static final Map<Class<?>, Set<String>> MAPPING = new HashMap<>(8);
  private final IDualMapper dualMapper;
  public DoMapAspect(DualMapper dualMapper) {
      this.dualMapper = dualMapper;
  }
  /**
   * 初始化映射关系
   * 扫描指定包下所有类，找出带有MapTo注解的字段
   * 存储映射数据
   */
  @PostConstruct
  public void initMap() {
      // 初始化所有MapTo对象
      // 扫描所有类
      Set<Class<?>> classes = ClassUtil.scanPackage("sushengbuyu.maptodemo");
      int totalField = 0;
      // 找出使用MapTo注解的对象
      for (Class<?> c : classes) {
          Field[] fields = c.getDeclaredFields();
          for (Field f : fields) {
              if (null != f.getAnnotation(MapTo.class)){
                  log.info("找到需要映射的字段: 类名：{} - 字段名：{}", c.getName(), f.getName());
                  // 保存映射关系
                  Set<String> set;
                  if (MAPPING.containsKey(c)) {
                      set = MAPPING.get(c);
                  } else {
                      set = new HashSet<>();
                  }
                  set.add(f.getName());
                  MAPPING.put(c, set);
                  totalField++;
              }
          }
      }
      log.info("总计{}个映射类，{}个映射字段", MAPPING.size(), totalField);
  }
  /**
   * 切点
   * @param doMap 执行映射注解
   */
  @Pointcut("@annotation(doMap)")
  public void point(DoMap doMap){}
  /**
   * 处理关联映射
   * @param point 切点
   * @param doMap 映射处理配置
   * @return Object
   * @throws Throwable 异常
   */
  @Around(value = "@annotation(doMap)")
  public Object doMap(ProceedingJoinPoint point, DoMap doMap) throws Throwable {
      // 执行切面方法
      Object obj = point.proceed();
      try {
          Object relObj = obj;
          if (StringUtils.hasLength(doMap.spel())) {
              // 如果使用了SPEL表达式，则从返回值中获取处理对象
              ExpressionParser parser = new SpelExpressionParser();
              Expression expression = parser.parseExpression(doMap.spel());
              relObj = expression.getValue(obj);
          }
          // 获取映射类
          Class<?> c = doMap.targetClass();
          // 映射处理
          doMapping(c, relObj);
      } catch (Exception e) {
          log.error("映射异常", e);
      }
      log.info("返回对象：{}", obj);
      return obj;
  }
  private void doMapping(Class<?> c, Object obj) throws Exception {
      if (obj instanceof Collection) {
          // 集合
          Collection<?> co = (Collection<?>) obj;
          for (Object o : co) {
              mapping(c, o);
          }
      } else {
          // 单个对象
          mapping(c, obj);
      }
  }
  private void mapping(Class<?> c, Object obj) throws Exception {
      // 判断是否有映射关系
      if (MAPPING.containsKey(c)) {
          log.info("处理映射类：{}", c.getName());
          // 从缓存中获取映射字段名称
          Set<String> filedNames = MAPPING.get(c);
          for (String fieldName : filedNames) {
              Field f = c.getDeclaredField(fieldName);
              log.info("处理映射字段：{}", f.getName());
              // 获取映射注解
              MapTo mapTo = f.getAnnotation(MapTo.class);
              log.info("映射配置：{}", mapTo);
              // 设置私有字段访问权限
              f.setAccessible(true);
              // 执行SQL
              String sql = mapTo.sql();
              // 处理SQL变量
              List<String> res = ReUtil.findAll("\$\{(.*?)}", sql, 0);
              log.info("SQL变量：{}", res);
              for (String re : res) {
                  Field ff = obj.getClass().getDeclaredField(re.substring(2, re.length()-1));
                  ff.setAccessible(true);
                  Object o = ff.get(obj);
                  sql = sql.replace(re, o.toString());
              }
              log.info("最终SQL：{}", sql);
              List<Map<String, Object>> results = dualMapper.executeSql(sql);
              Object v = null;
              if (Collection.class.isAssignableFrom(f.getType())) {
                  // 集合对象
                  if (results.size() > 0) {
                      v = results.stream()
                              .map(r -> mapToBean(r, mapTo.targetClass()))
                              .collect(Collectors.toList());
                  }
              } else {
                  // 单个对象
                  if (results.size() > 1) {
                      log.error("预计返回一条数据，实际返回多条数据。执行SQL: {}", sql);
                  } else if (results.size() == 1) {
                      // 转换结果，赋值
                      v = mapToBean(results.get(0), mapTo.targetClass());
                  }
              }
              if (v != null && mapTo.doDeep()) {
                  doMapping(mapTo.targetClass(), v);
              }
              f.set(obj, v);
          }
      }
  }
  /**
   * Map对象转Bean
   * @param map map
   * @param clazz bean
   * @return bean
   */
  private Object mapToBean(Map<?, ?> map, Class<?> clazz) {
      try {
          return BeanUtil.fillBeanWithMap(map, clazz.newInstance(), true);
      } catch (InstantiationException | IllegalAccessException e) {
          log.error("实例化异常", e);
          return null;
      }
  }
}

三、使用方法

测试类

SysUser

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import java.io.Serializable;
import java.util.List;
import java.util.StringJoiner;
/**
* @author victor
* @desc 系统用户
* @date 2022/5/17
*/
public class SysUser implements Serializable {
  private static final long serialVersionUID = 4855472141572371097L;
  @TableId(type = IdType.ASSIGN_ID)
  private Long id;
  /**
   * 登录用户名
   */
  private String username;
  /**
   * 登录密码
   */
  private String password;
  /**
   * 昵称
   */
  private String nickName;
  
  @MapTo(targetClass = SysRole.class
          , doDeep = true
          , sql = "SELECT * FROM sys_role WHERE user_id=${id}")
  @TableField(exist = false)
  private SysRole sysRole;
  @MapTo(targetClass = SysRole.class
          , doDeep = true
          , sql = "SELECT * FROM sys_role WHERE user_id=${id}")
  @TableField(exist = false)
  private List<SysRole> roleList;

  public Long getId() {
      return id;
  }
  public void setId(Long id) {
      this.id = id;
  }
  public String getUsername() {
      return username;
  }
  public void setUsername(String username) {
      this.username = username;
  }
  public String getPassword() {
      return password;
  }
  public void setPassword(String password) {
      this.password = password;
  }
  public String getNickName() {
      return nickName;
  }
  public void setNickName(String nickName) {
      this.nickName = nickName;
  }
  public SysRole getSysRole() {
      return sysRole;
  }
  public void setSysRole(SysRole sysRole) {
      this.sysRole = sysRole;
  }
  public List<SysRole> getRoleList() {
      return roleList;
  }
  public void setRoleList(List<SysRole> roleList) {
      this.roleList = roleList;
  }
  @Override
  public String toString() {
      return new StringJoiner(", ", SysUser.class.getSimpleName() + "[", "]")
              .add("id=" + id)
              .add("username='" + username + "'")
              .add("password='" + password + "'")
              .add("nickName='" + nickName + "'")
              .add("sysRole=" + sysRole)
              .add("roleList=" + roleList)
              .toString();
  }
}

SysRole

package sushengbuyu.maptodemo.sys.po;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import sushengbuyu.maptodemo.aop.MapTo;
import java.util.List;
import java.util.StringJoiner;
/**
* @author victor
* @desc 说明
* @date 2022/5/23
*/
public class SysRole {
  @TableId
  private Long id;
  private Long userId;
  private String name;
  @MapTo(targetClass = SysPermission.class
          , sql = "SELECT p.* FROM sys_permission p " +
          "LEFT JOIN sys_role_permission rp ON p.id = rp.perm_id " +
          "WHERE rp.role_id = ${id}")
  @TableField(exist = false)
  private List<SysPermission> permissionList;
  public String getName() {
      return name;
  }
  public void setName(String name) {
      this.name = name;
  }
  public Long getId() {
      return id;
  }
  public void setId(Long id) {
      this.id = id;
  }
  public Long getUserId() {
      return userId;
  }
  public void setUserId(Long userId) {
      this.userId = userId;
  }
  public List<SysPermission> getPermissionList() {
      return permissionList;
  }
  public void setPermissionList(List<SysPermission> permissionList) {
      this.permissionList = permissionList;
  }
  @Override
  public String toString() {
      return new StringJoiner(", ", SysRole.class.getSimpleName() + "[", "]")
              .add("id=" + id)
              .add("userId=" + userId)
              .add("name='" + name + "'")
              .toString();
  }
}

SysPermission

package sushengbuyu.maptodemo.sys.po;
import java.util.StringJoiner;
/**
* @author victor
* @desc 说明
* @date 2022/5/25
*/
public class SysPermission {
  private Long id;
  private String name;
  private Integer type;
  public Long getId() {
      return id;
  }
  public void setId(Long id) {
      this.id = id;
  }
  public String getName() {
      return name;
  }
  public void setName(String name) {
      this.name = name;
  }
  public Integer getType() {
      return type;
  }
  public void setType(Integer type) {
      this.type = type;
  }
  @Override
  public String toString() {
      return new StringJoiner(", ", SysPermission.class.getSimpleName() + "[", "]")
              .add("id=" + id)
              .add("name='" + name + "'")
              .add("type=" + type)
              .toString();
  }
}

SysUserService

测试用例就常见的三种, 查单个，查列表，查分页

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import org.springframework.stereotype.Service;
import java.io.Serializable;
import java.util.List;
/**
* @author victor
* @desc 说明
* @date 2022/5/17
*/
@Service
public class SysUserService extends ServiceImpl<SysUserMapper, SysUser> {
  @DoMap(targetClass = SysUser.class)
  @Override
  public SysUser getById(Serializable id) {
      return super.getById(id);
  }
  @DoMap(targetClass = SysUser.class)
  public List<SysUser> listAll() {
      QueryWrapper<SysUser> wrapper = new QueryWrapper<>();
      return baseMapper.selectList(wrapper);
  }
  /**
   * 从Page中取records作为处理对象
   */
  @DoMap(targetClass = SysUser.class, spel = "records")
  public Page<SysUser> page() {
      QueryWrapper<SysUser> wrapper = new QueryWrapper<>();
      Page<SysUser> p = new Page<>(1, 10);
      return baseMapper.selectPage(p, wrapper);
  }
}

DoMapTests

import cn.hutool.json.JSONUtil;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
//@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
class DoMapTests {
  @Autowired
  private SysUserService service;
  @Test
  void single() {
      System.out.println(JSONUtil.toJsonPrettyStr(service.getById(1)));
  }
  @Test
  void list() {
      System.out.println(JSONUtil.toJsonPrettyStr(service.listAll()));
  }
  @Test
  void page() {
      System.out.println(JSONUtil.toJsonPrettyStr(service.page()));
  }
}

测试数据

使用AOP+反射实现自定义Mybatis多表关联查询

测试结果

single

{
  "nickName": "aa11",
  "roleList": [
      {
          "permissionList": [
              {
                  "type": 0,
                  "name": "add",
                  "id": 1
              },
              {
                  "type": 0,
                  "name": "query",
                  "id": 2
              }
          ],
          "userId": 1,
          "name": "r1",
          "id": 11
      },
      {
          "permissionList": [
              {
                  "type": 0,
                  "name": "del",
                  "id": 3
              }
          ],
          "userId": 1,
          "name": "r2",
          "id": 12
      }
  ],
  "password": "123456",
  "id": 1,
  "username": "a1"
}

list

[
  {
      "nickName": "aa11",
      "roleList": [
          {
              "permissionList": [
                  {
                      "type": 0,
                      "name": "add",
                      "id": 1
                  },
                  {
                      "type": 0,
                      "name": "query",
                      "id": 2
                  }
              ],
              "userId": 1,
              "name": "r1",
              "id": 11
          },
          {
              "permissionList": [
                  {
                      "type": 0,
                      "name": "del",
                      "id": 3
                  }
              ],
              "userId": 1,
              "name": "r2",
              "id": 12
          }
      ],
      "password": "123456",
      "id": 1,
      "username": "a1"
  },
  {
      "sysRole": {
          "userId": 2,
          "name": "r3",
          "id": 13
      },
      "nickName": "aa22",
      "roleList": [
          {
              "userId": 2,
              "name": "r3",
              "id": 13
          }
      ],
      "password": "123456",
      "id": 2,
      "username": "a2"
  }
]

page

{
  "optimizeCountSql": true,
  "records": [
      {
          "nickName": "aa11",
          "roleList": [
              {
                  "permissionList": [
                      {
                          "type": 0,
                          "name": "add",
                          "id": 1
                      },
                      {
                          "type": 0,
                          "name": "query",
                          "id": 2
                      }
                  ],
                  "userId": 1,
                  "name": "r1",
                  "id": 11
              },
              {
                  "permissionList": [
                      {
                          "type": 0,
                          "name": "del",
                          "id": 3
                      }
                  ],
                  "userId": 1,
                  "name": "r2",
                  "id": 12
              }
          ],
          "password": "123456",
          "id": 1,
          "username": "a1"
      },
      {
          "sysRole": {
              "userId": 2,
              "name": "r3",
              "id": 13
          },
          "nickName": "aa22",
          "roleList": [
              {
                  "userId": 2,
                  "name": "r3",
                  "id": 13
              }
          ],
          "password": "123456",
          "id": 2,
          "username": "a2"
      }
  ],
  "searchCount": true,
  "total": 0,
  "current": 1,
  "size": 10,
  "orders": [
  ]
}

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原文链接：https://juejin.cn/post/7101204422402768933