Spring Data JPA |自定义非实体类的映射-白红宇

Spring Data JPA |自定义非实体类的映射

阅读量：4180 次

发布时间：2019-05-26

本文共 3257 字，大约阅读时间需要 10 分钟。

一、首先是实体类的定义：

package com.example.entity;import lombok.*;import javax.persistence.*;import java.io.Serializable;/** * @author xiaobu * @version JDK1.8.0_171 * @date on  2018/11/13 10:51 * @description V1.0 */@Entity@Table(name = "test_book")@NoArgsConstructor@Setter@Getter@ToStringpublic class Book implements Serializable {    private static final long serialVersionUID = 6214167880862325845L;    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    private int id;    @Column(name="name",columnDefinition=("varchar(50)  default null comment '名称'"))    private String name;    @Column(name="author",columnDefinition=("varchar(252)  default null comment '作者'"))    private String author;}

二、自定义非实体类的定义：

package com.example.entity.vo;import lombok.Getter;import lombok.NoArgsConstructor;import lombok.Setter;import lombok.ToString;import java.io.Serializable;/** * @author xiaobu * @version JDK1.8.0_171 * @date on  2018/11/16 10:05 * @description V1.0 */@Getter@Setter@ToStringpublic class BookVo implements Serializable {    private static final long serialVersionUID = 294655766971777057L;    public BookVo (String name, String author) {        super();        this.name = name;        this.author = author;    }    private String name;    private String author;}

三、使用HQL方式查询：

List
   
     list = bookRepository.findByHql("select new com.example.entity.vo.BookVo (b.name,b.author) from Book b");

四、使用SQL方式查询（需要把结果通过反射转为对应的自定义的非实体类）

List
   
     list1 = bookRepository.findListBySql("select b.name,b.author from test_book b");       for(Object[] objects:list1){           System.out.println(Arrays.toString(objects));       }        List
    
      vos = EntityUtils.castEntity(list1,BookVo.class);        System.out.println(vos);

五、EntityUtils工具类的内容如下：

package com.example.util;import lombok.extern.slf4j.Slf4j;import java.lang.reflect.Constructor;import java.lang.reflect.Field;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;/** * @author xiaobu * @version JDK1.8.0_171 * @date on  2018/11/16 11:06 * @description V1.0 */@Slf4jpublic class EntityUtils {    /**     * 数组集合转化为指定对象集合     * 指定的实体对象必须包含所以字段的构造方法，数组的元素的顺序将和构造方法顺序和类型一一对应     *     * @param list  集合     * @param clazz c     * @param 
   
       类型     * @return List
    
          */    public static 
     
       List
      
        castEntity(List
       
         list, Class
        
          clazz) { List
         
           returnList = new ArrayList<>(); if (list.size() == 0) { return returnList; } Class[] c2 = null; Constructor[] constructors = clazz.getConstructors(); for (Constructor constructor : constructors) { Class[] tClass = constructor.getParameterTypes(); if (tClass.length == list.get(0).length) { c2 = tClass; break; } } //构造方法实例化对象 for (Object[] o : list) { Constructor
          
            constructor = null; try { constructor = clazz.getConstructor(c2); } catch (NoSuchMethodException e) { e.printStackTrace(); } try { assert constructor != null; returnList.add(constructor.newInstance(o)); } catch (InstantiationException | IllegalAccessException | InvocationTargetException e) { e.printStackTrace(); } } return returnList; }}