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2021
07-01

深入理解Java对象复制

一、图示

图片

二、MapStruct

pom文件

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
 
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.16</version>
        </dependency>
 
        <!-- https://mvnrepository.com/artifact/commons-beanutils/commons-beanutils -->
        <dependency>
            <groupId>commons-beanutils</groupId>
            <artifactId>commons-beanutils</artifactId>
            <version>1.9.4</version>
        </dependency>
 
        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct</artifactId>
            <version>1.2.0.Final</version>
        </dependency>
        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct-jdk8</artifactId>
            <version>1.2.0.Final</version>
        </dependency>
        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct-processor</artifactId>
            <version>1.2.0.Final</version>
        </dependency>
 
        <!-- dozer使用时需要配置xml 文件,不推荐使用性能和 BeanUtils 差不多,使用过程可以参考 https://www.jianshu.com/p/bf8f0e8aee23-->
        <!-- https://mvnrepository.com/artifact/net.sf.dozer/dozer -->
        <!--<dependency>
            <groupId>net.sf.dozer</groupId>
            <artifactId>dozer</artifactId>
            <version>5.5.1</version>
        </dependency>-->

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

<build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.6.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                    <showWarnings>true</showWarnings>
                    <annotationProcessorPaths>
                        <path>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                            <version>1.18.16</version>
                        </path>
                        <path>
                            <groupId>org.mapstruct</groupId>
                            <artifactId>mapstruct-processor</artifactId>
                            <version>1.2.0.Final</version>
                        </path>
                    </annotationProcessorPaths>
                </configuration>
            </plugin>
 
        </plugins>
 
    </build>

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
 *
 * <p>
 * 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<StudentDTO> 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());
 
    }

四、问题

beanUtils  不会进行 属性 类型的转换,如果字段名称相同,类型不同,不会对该字段进行赋值操作,( 测试方法中使用的 是 org.springframework.beans.BeanUtils )

cglib  在不定义Converter 的情况下也会出现 类型转换错误的异常,可以手动自定义转换器 convert ,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。

springframwork 有实现 cglib 的BeanCopier 不需要再引用 org.easymock 依赖

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