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這篇“怎么使用AOP+反射實現自定義Mybatis多表關聯查詢”文章的知識點大部分人都不太理解，所以小編給大家總結了以下內容，內容詳細，步驟清晰，具有一定的借鑒價值，希望大家閱讀完這篇文章能有所收獲，下面我們一起來看看這篇“怎么使用AOP+反射實現自定義Mybatis多表關聯查詢”文章吧。
目前使用的ORM框架是Mybatis Plus，是Mybatis的增強框架，基礎的CRUD的方法都集成了，開發起來很是方便。但是項目中總是需要多表關聯查詢。
Mybatis的多表關聯有兩種
一、在Mapper中使用@Result @One @Many注解
二、在xml文件中配置對應的resultMap和關聯標簽
使用起來很不方便。JPA倒是有多表關聯的注解實現，但是不想再引入另一個ORM框架。
目前的需求是增強現有的查詢，使用簡單的注解即可實現多表關聯。
實現該功能總共需要四個文件
兩個自定義注解，一個虛擬Mapper，一個切面處理類
自定義映射注解，標注需要映射處理的字段
import java.lang.annotation.*;
/**
* @author victor
* @desc 自定義多表關聯映射注解
* @date 2022/5/23
*/
@Documented
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface MapTo {
/**
* 映射目標
*/
Class<?> targetClass();
/**
* 執行SQL
*/
String sql();
/**
* 嵌套處理
* 為true時，如果映射的對象類中有映射字段，也執行映射操作
*/
boolean doDeep() default false;
}自定義映射處理注解，標注需要執行映射的方法
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* @author victor
* @desc 標注該需要執行映射處理的方法
* @date 2022/5/23
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface DoMap {
/**
* 需要處理映射的類
* @return Class
*/
Class<?> targetClass();
/**
* spel表達式
* 默認為空
* @return String
*/
String spel() default "";
}虛擬Mapper，用來執行自定義SQL
import java.util.List;
import java.util.Map;
/**
* @author victor
* @desc 虛擬Mapper
* @date 2022/5/23
*/
@Mapper
public interface IDualMapper {
/**
* 執行自定義SQL
* @param sql sql
* @return List<Map<String, Object>>
*/
List<Map<String, Object>> executeSql(String sql);
}使用者自行實現DualMapper，解除mybatis強依賴
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 虛擬Mapper
* @date 2022/5/23
*/
@Mapper
public interface DualMapper extends IDualMapper {
/**
* 執行自定義SQL
* @param sql sql
* @return List<Map<String, Object>>
*/
@Select("${sql}")
List<Map<String, Object>> executeSql(@Param("sql") String sql);
}切面處理類，核心代碼，執行映射操作
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 自定義關聯映射切面
* @date 2022/5/23
*/
@Component
@Aspect
public class DoMapAspect {
private final static Logger log = LoggerFactory.getLogger(DoMapAspect.class);
/**
* 保存MapTo映射關系
* key 映射字段所在類
* 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;
}
/**
* 初始化映射關系
* 掃描指定包下所有類，找出帶有MapTo注解的字段
* 存儲映射數據
*/
@PostConstruct
public void initMap() {
// 初始化所有MapTo對象
// 掃描所有類
Set<Class<?>> classes = ClassUtil.scanPackage("sushengbuyu.maptodemo");
int totalField = 0;
// 找出使用MapTo注解的對象
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: 類名：{} - 字段名：{}", c.getName(), f.getName());
// 保存映射關系
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("總計{}個映射類，{}個映射字段", MAPPING.size(), totalField);
}
/**
* 切點
* @param doMap 執行映射注解
*/
@Pointcut("@annotation(doMap)")
public void point(DoMap doMap){}
/**
* 處理關聯映射
* @param point 切點
* @param doMap 映射處理配置
* @return Object
* @throws Throwable 異常
*/
@Around(value = "@annotation(doMap)")
public Object doMap(ProceedingJoinPoint point, DoMap doMap) throws Throwable {
// 執行切面方法
Object obj = point.proceed();
try {
Object relObj = obj;
if (StringUtils.hasLength(doMap.spel())) {
// 如果使用了SPEL表達式，則從返回值中獲取處理對象
ExpressionParser parser = new SpelExpressionParser();
Expression expression = parser.parseExpression(doMap.spel());
relObj = expression.getValue(obj);
}
// 獲取映射類
Class<?> c = doMap.targetClass();
// 映射處理
doMapping(c, relObj);
} catch (Exception e) {
log.error("映射異常", e);
}
log.info("返回對象：{}", 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 {
// 單個對象
mapping(c, obj);
}
}
private void mapping(Class<?> c, Object obj) throws Exception {
// 判斷是否有映射關系
if (MAPPING.containsKey(c)) {
log.info("處理映射類：{}", c.getName());
// 從緩存中獲取映射字段名稱
Set<String> filedNames = MAPPING.get(c);
for (String fieldName : filedNames) {
Field f = c.getDeclaredField(fieldName);
log.info("處理映射字段：{}", f.getName());
// 獲取映射注解
MapTo mapTo = f.getAnnotation(MapTo.class);
log.info("映射配置：{}", mapTo);
// 設置私有字段訪問權限
f.setAccessible(true);
// 執行SQL
String sql = mapTo.sql();
// 處理SQL變量
List<String> res = ReUtil.findAll("\$\{(.*?)}", sql, 0);
log.info("SQL變量：{}", 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("最終SQL：{}", sql);
List<Map<String, Object>> results = dualMapper.executeSql(sql);
Object v = null;
if (Collection.class.isAssignableFrom(f.getType())) {
// 集合對象
if (results.size() > 0) {
v = results.stream()
.map(r -> mapToBean(r, mapTo.targetClass()))
.collect(Collectors.toList());
}
} else {
// 單個對象
if (results.size() > 1) {
log.error("預計返回一條數據，實際返回多條數據。執行SQL: {}", sql);
} else if (results.size() == 1) {
// 轉換結果，賦值
v = mapToBean(results.get(0), mapTo.targetClass());
}
}
if (v != null && mapTo.doDeep()) {
doMapping(mapTo.targetClass(), v);
}
f.set(obj, v);
}
}
}
/**
* Map對象轉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("實例化異常", e);
return null;
}
}
}測試類
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 系統用戶
* @date 2022/5/17
*/
public class SysUser implements Serializable {
private static final long serialVersionUID = 4855472141572371097L;
@TableId(type = IdType.ASSIGN_ID)
private Long id;
/**
* 登錄用戶名
*/
private String username;
/**
* 登錄密碼
*/
private String password;
/**
* 昵稱
*/
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();
}
}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 說明
* @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();
}
}package sushengbuyu.maptodemo.sys.po;
import java.util.StringJoiner;
/**
* @author victor
* @desc 說明
* @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();
}
}測試用例就常見的三種, 查單個，查列表，查分頁
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 說明
* @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);
}
/**
* 從Page中取records作為處理對象
*/
@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);
}
}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()));
}
}
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": [
]
}以上就是關于“怎么使用AOP+反射實現自定義Mybatis多表關聯查詢”這篇文章的內容，相信大家都有了一定的了解，希望小編分享的內容對大家有幫助，若想了解更多相關的知識內容，請關注億速云行業資訊頻道。
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