这篇“怎么使用AOP+反射实现自定义Mybatis多表关联查询”文章的知识点大部分人都不太理解，所以小编给大家总结了以下内容，内容详细，步骤清晰，具有一定的借鉴价值，希望大家阅读完这篇文章能有所收获，下面我们一起来看看这篇“怎么使用AOP+反射实现自定义Mybatis多表关联查询”文章吧。
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
实现该功能总共需要四个文件
两个自定义注解，一个虚拟Mapper，一个切面处理类
MapTo
自定义映射注解，标注需要映射处理的字段
import java.lang.annotation.*;@Documented@Target(ElementType.FIELD)@Retention(RetentionPolicy.RUNTIME)public @interface MapTo { Class<?> targetClass(); String sql(); 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;@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.METHOD)public @interface DoMap { Class<?> targetClass(); String spel() default "";}IDualMapper
虚拟Mapper，用来执行自定义SQL
import java.util.List;import java.util.Map;@Mapperpublic interface IDualMapper { 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;@Mapperpublic interface DualMapper extends IDualMapper { @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;@Component@Aspectpublic class DoMapAspect { private final static Logger log = LoggerFactory.getLogger(DoMapAspect.class); private static final Map<Class<?>, Set<String>> MAPPING = new HashMap<>(8); private final IDualMapper dualMapper; public DoMapAspect(DualMapper dualMapper) { this.dualMapper = dualMapper; } @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); } @Pointcut("@annotation(doMap)") public void point(DoMap doMap){} @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); } } } 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;public class SysUser implements Serializable { private static final long serialVersionUID = 4855472141572371097L; @TableId(type = IdType.ASSIGN_ID) private Long id; private String username; private String password; 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;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;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;@Servicepublic 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); } @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
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": [ ]}以上就是关于“怎么使用AOP+反射实现自定义Mybatis多表关联查询”这篇文章的内容，相信大家都有了一定的了解，希望小编分享的内容对大家有帮助，若想了解更多相关的知识内容，请关注编程网行业资讯频道。
