技术背景
在使用MyBatisPlus技术实际项目中，尤其是后台管理系统之类的项目中，经常会出现大量的需要将查询对象转换成QueryWrapper的应用场景，这时候就需要编写出现大量的转换代码，比如：
待转换的查询实体类
@Getter
@Setter
@ToString(callSuper = true)
public class MemberQuery extends BaseQuery {
/**
* 昵称
*/
private String nickname;
/**
* 性别：1女 2男 3未知
*/
private Integer gender;
/**
* 生日：下限
*/
private LocalDate start;
/**
* 生日：上限
*/
private LocalDate end;
/**
* 电话
*/
private String tel;
/**
* 外键：角色编号
*/
private Long roleId;
/**
* 状态：1未激活 2激活
*/
private Integer state;
@Builder
public MemberQuery(Integer pageNum, Integer pageSize, String nickname, Integer gender, LocalDate start, LocalDate end, String tel, Long roleId, Integer state) {
super(pageNum, pageSize);
this.nickname = nickname;
this.gender = gender;
this.start = start;
this.end = end;
this.tel = tel;
this.roleId = roleId;
this.state = state;
}
}
上面查询类引用的BaseQuery封装了分页信息，具体代码如下：
@Setter
@ToString
@AllArgsConstructor
public class BaseQuery {
/**
* 页码
*/
private Integer pageNum;
/**
* 页面大小
*/
private Integer pageSize;
public Integer getPageNum() {
return pageNum == null ? 1 : pageNum;
}
public Integer getPageSize() {
return pageSize == null ? GlobalConst.PAGE_SIZE : pageSize;
}
}
在Controller中进行转换
@PostMapping("/list")
public ResultBean list(@RequestBody MemberQuery memberQuery) {
IPage<Member> page = new Page<>(memberQuery.getPageNum(), memberQuery.getPageSize());
LambdaQueryWrapper<Member> queryWrapper = new LambdaQueryWrapper<>();
if (memberQuery.getNickname() != null) {
queryWrapper.like(Member::getNickname, memberQuery.getNickname());
}
if (memberQuery.getTel() != null) {
queryWrapper.like(Member::getTel, memberQuery.getTel());
}
if (memberQuery.getGender() != null) {
queryWrapper.eq(Member::getGender, memberQuery.getGender());
}
if (memberQuery.getRoleId() != null) {
queryWrapper.eq(Member::getRoleId, memberQuery.getRoleId());
}
if (memberQuery.getState() != null) {
queryWrapper.eq(Member::getState, memberQuery.getState());
}
if (memberQuery.getStart() != null) {
queryWrapper.ge(Member::getBirth,memberQuery.getStart());
}
if(memberQuery.getEnd() != null){
queryWrapper.le(Member::getBirth,memberQuery.getEnd());
}
memberService.page(page, queryWrapper);
PageBean<Member> pageBean = PageBean.init(page);
return ResultBeanUtil.success().buildData("pageBean",pageBean);
}
上面大量的转换代码，不仅写起来烦琐，而且也不优雅。此时可以采用注解+反射技术编写一个工具类：将Query对象转换成Wrapper，具体代码如下：
优化方案
表示关系运算的接口
public interface Logic {
String and = "AND";
String or = "OR";
}
表示逻辑运算的枚举
- Between
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Between {
String logic() default Logic.and;
}
- EQ
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface EQ {
String logic() default Logic.and;
String value() default "";
}
- IN
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface IN {
String logic() default Logic.and;
String value() default "";
}
- Like
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Like {
String logic() default "AND";
String value() default "";
}
- NE
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface NE {
String logic() default Logic.and;
String value() default "";
}
封装区间的Bean
@Getter
@Setter
@NoArgsConstructor
@AllArgsConstructor
public class RangeBean<T> {
/**
* 下限
*/
private T start;
/**
* 上限
*/
private T end;
}
具体转换的工具类
public class QueryWrapperUtil<T> {
/**
* 将查询对象转换成MyBatisPlus中的QueryWrapper
* @param query
* @param <T>
* @return
*/
public static <T> QueryWrapper<T> build(Object query) {
QueryWrapper<T> queryWrapper = new QueryWrapper<>();
//获取Query类中都有哪些属性
final Field[] fields = query.getClass().getDeclaredFields();
for (Field field : fields) {
field.setAccessible(true);
java.lang.Object fieldValue = null;
try {
fieldValue = field.get(query);
} catch (IllegalAccessException e) {
e.printStackTrace();
}
if (fieldValue != null) {
//获取Query类属性上的注解
final Annotation[] annotations = field.getAnnotations();
for (Annotation annotation : annotations) {
//获取Query类属性的名称
final String fieldName = field.getName();
//获取Query类对应的表字段名
final String columnName = StringUtil.hump2underscore(fieldName);
//获取Query类属性上的注解类型的字节码
final Class<? extends Annotation> annotationType = annotation.annotationType();
if (EQ.class == annotationType) {
EQ eq = (EQ) annotation;
fun(eq.logic(), queryWrapper);
queryWrapper.eq(columnName, fieldValue);
} else if (Like.class == annotationType) {
Like like = (Like) annotation;
fun(like.logic(), queryWrapper);
queryWrapper.like(columnName, fieldValue);
} else if (IN.class == annotationType) {
IN in = (IN) annotation;
fun(in.logic(), queryWrapper);
queryWrapper.in(columnName, fieldValue);
} else if (NE.class == annotationType) {
NE ne = (NE) annotation;
fun(ne.logic(), queryWrapper);
queryWrapper.ne(columnName, fieldValue);
} else if (Between.class == annotationType) {
Between between = (Between) annotation;
fun(between.logic(), queryWrapper);
RangeBean rangeBean = (RangeBean) fieldValue;
queryWrapper.between(columnName, rangeBean.getStart(), rangeBean.getEnd());
}
}
}
}
return queryWrapper;
}
/**
* 添加or关系
* @param logic
* @param queryWrapper
* @param <T>
*/
private static <T> void fun(String logic, QueryWrapper<T> queryWrapper) {
if ("or".equalsIgnoreCase(logic)) {
queryWrapper.or();
}
}
}
优化方案：工具类应用
@PostMapping("/list")
public ResultBean list(@RequestBody MemberQuery memberQuery) {
IPage<Member> page = new Page<>(memberQuery.getPageNum(), memberQuery.getPageSize());
QueryWrapper<Member> queryWrapper = QueryWrapperUtil.build(memberQuery);
memberService.page(page, queryWrapper);
PageBean<Member> pageBean = PageBean.init(page);
return ResultBeanUtil.success().addData("pageBean",pageBean);
}