深入理解Java对象复制

使用任何已有的工具,都没有直接使用 get set 方式进行,对象转换的速度快,虽然get set 方式代码对一些比较麻烦,但是效率要高一些的,推荐使用 MapStruct 方式.,需要的朋友可以参考下

一、图示

二、MapStruct

pom文件

  junitjunit4.12 org.projectlomboklombok1.18.16 commons-beanutilscommons-beanutils1.9.4 org.mapstructmapstruct1.2.0.Final org.mapstructmapstruct-jdk81.2.0.Final org.mapstructmapstruct-processor1.2.0.Final

下载插件

插件的作用是为了在本地测试的时候，生成接口的 impl 文件（生成的文件存在与target包里面）

如果是生产环境的话，和Lombok操作一样，需要在pom文件添加 mapStruct 插件依赖

    org.apache.maven.pluginsmaven-compiler-plugin3.6.1 1.81.8true  org.projectlomboklombok1.18.16 org.mapstructmapstruct-processor1.2.0.Final

代码

 import com.baomidou.mybatisplus.annotation.TableName; import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; /** * Created by yangLongFei on 2021/5/11 10:44 * Version: $ */ @Data @AllArgsConstructor @NoArgsConstructor @TableName public class Student { private Integer id; private String name; private String age; private String phone; private String address; }

 import lombok.Data; import java.io.Serializable; /** * Created by yangLongFei on 2021/5/11 10:51 * Version: $ */ @Data public class StudentDTO implements Serializable { private static final long serialVersionUID = 735190899850778343L; private Integer id; private String name; private String age; private String phone; private String address; }

 import lombok.Data; import java.io.Serializable; /** * Created by yangLongFei on 2021/5/11 16:59 * Version: $ */ @Data public class StudentVO implements Serializable { private static final long serialVersionUID = 2059190505074790405L; private Integer pk; private String userName; private String userAge; private String userPhone; private String userAddress; }

接口

 import com.sys.yang.dto.StudentDTO; import com.sys.yang.entity.Student; import com.sys.yang.vo.StudentVO; import org.mapstruct.Mapper; import org.mapstruct.Mapping; import org.mapstruct.Mappings; import org.mapstruct.factory.Mappers; @Mapper public interface ConverterStudent { ConverterStudent INSTANCE = Mappers.getMapper(ConverterStudent.class); @Mappings({ @Mapping(source = "name", target = "name"), @Mapping(source = "age", target = "age") }) StudentDTO entityToDTO(Student student); @Mappings({ @Mapping(source = "id", target = "pk"), @Mapping(source = "name", target = "userName"), @Mapping(source = "age", target = "userAge"), @Mapping(source = "phone", target = "userPhone"), @Mapping(source = "address", target = "userAddress") }) StudentVO dtoToVo(StudentDTO studentDTO); }

测试类

 import com.sys.yang.dto.StudentDTO; import com.sys.yang.entity.Student; import com.sys.yang.vo.StudentVO; import org.junit.Test; import org.springframework.beans.BeanUtils; import java.lang.reflect.Method; /** * 对象转换，映射 * 方式1：效率最高 get set 方法 * 方式2：Common包 BeanUtils.copyProperties 反射的方式进行 * 方式3：mapstruct 推荐使用，操作不复杂，效率和 get set 方式相差不大 * *  * Created by yangLongFei on 2021/5/11 10:43 * Version: $ */ public class AToB { /** * set get 的时候使用 * 生成 对象的set方法 */ public static void main(String[] args) { Class clazz = StudentDTO.class; Method[] fields = clazz.getDeclaredMethods(); for (Method field: fields) { String name = field.getName(); if(!name.startsWith("is") && !name.startsWith("get")){ System.out.println("entity." + name + "()"); } } } /** * 测试方法 */ @Test public void test1() { Student student = new Student(1,"zhagnsan","18","110112113114","diqiu"); System.out.println(student.toString()); StudentDTO studentDTO1 = new StudentDTO(); BeanUtils.copyProperties(student,studentDTO1); System.out.println("BeanUtils: "+ studentDTO1.toString()); StudentDTO studentDTO2 = ConverterStudent.INSTANCE.entityToDTO(student); System.out.println("mapstruct: entityToDTO " + studentDTO2.toString()); StudentVO studentVO = ConverterStudent.INSTANCE.dtoToVo(studentDTO2); System.out.println("mapStruct: dtoToVo "+ studentVO); } }

生成的接口文件

三、framework cglib

要转换的对象的，字段名称要和原对象的字段名称一致，否则赋值会失败，可以手动 convert 方法，但是，实现后所有的转换内容都会走 convert 方法

代码

 import lombok.Data; import java.io.Serializable; /** * Created by yangLongFei on 2021/5/11 16:59 * Version: $ */ @Data public class StudentVO implements Serializable { private static final long serialVersionUID = 2059190505074790405L; private Integer pk; private String userName; private String userAge; private String userPhone; private String userAddress; // framework cglib 使用到的内容 private String id; private String name; private Integer age; private String phone; private String address; }

convert 实现类

 import org.springframework.cglib.core.Converter; /** * Created by yangLongFei on 2021/5/11 19:53 * Version: $ */ public class ConvertStudentDtoToVo implements Converter { /** * ⭐️⭐️⭐️⭐️⭐️ 要转换的属性名称，相同的情况下，才会走该方法 * @param o 原对象属性值，value * @param aClass 目标对象属性 类型，class java.lang.String * @param o1 目标对象属性set方法，setAddress * @return */ @Override public Object convert(Object o, Class aClass, Object o1) { if (o.getClass().equals(aClass)) { return o; } else { if (o instanceof Integer) { return String.valueOf(o); } if (String.valueOf(o1).contains("Age")) { return Integer.valueOf(o.toString()); } return o; } } }

测试方法

 @Test public void test2() { Student student = new Student(1,"zhagnsan","18","110112113114","diqiu"); // false 表示不使用 转换器， BeanCopier entityToDto = BeanCopier.create(Student.class, StudentDTO.class, false); StudentDTO studentDTO3 = new StudentDTO(); // null 表示，不指定转换器，要使用转换器的化，需要实现 Converter 接口 // 属性名称之间不能指定映射关系，当属性名称不同的时候赋值操作会失败 entityToDto.copy(student, studentDTO3, null); System.out.println("cglib ：entityToDTO " + studentDTO3.toString()); BeanCopier dtoTOVo = BeanCopier.create(StudentDTO.class, StudentVO.class, false); StudentVO studentVO1 = new StudentVO(); dtoTOVo.copy(studentDTO3, studentVO1, null); System.out.println("cglib: dtoToVo " + studentVO1.toString()); // 一旦使用Converter，BeanCopier只使用Converter定义的规则去拷贝属性，所以在convert方法中要考虑所有的属性 BeanCopier dtoTOVo2 = BeanCopier.create(StudentDTO.class, StudentVO.class, true); StudentVO studentVO2 = new StudentVO(); dtoTOVo2.copy(studentDTO3, studentVO2, new ConvertStudentDtoToVo()); System.out.println("cglib : convert "+studentVO2.toString()); }