Java 如何优雅的拷贝对象属性
作者：rxliuli
这篇文章主要介绍了Java 如何优雅的拷贝对象属性，帮助大家更好的理解和学习Java，感兴趣的朋友可以了解下
场景
在 Java 项目中，经常遇到需要在对象之间拷贝属性的问题。然而，除了直接使用 Getter/Stter 方法，我们还有其他的方法么？
当然有，例如 Apache Common Lang3 的 BeanUtils，然而 BeanUtils 却无法完全满足吾辈的需求，所以吾辈便自己封装了一个，这里分享出来以供参考。
- 需要大量复制对象的属性
- 对象之间的属性名可能是不同的
- 对象之间的属性类型可能是不同的
目标
简单易用的 API
- copy: 指定需要拷贝的源对象和目标对象
- prop: 拷贝指定对象的字段
- props: 拷贝指定对象的多个字段
- exec: 执行真正的拷贝操作
- from: 重新开始添加其他对象的属性
- get: 返回当前的目标对象
- config: 配置拷贝的一些策略
思路
- 定义门面类 BeanCopyUtil 用以暴露出一些 API
- 定义每个字段的操作类 BeanCopyField，保存对每个字段的操作
- 定义 BeanCopyConfig，用于配置拷贝属性的策略
- 定义 BeanCopyOperator 作为拷贝的真正实现
图解
实现
注：反射部分依赖于 joor, JDK1.8 请使用 joor-java-8
定义门面类 BeanCopyUtil 用以暴露出一些 API
/**
* java bean 复制操作的工具类
*
* @author rxliuli
*/
public class BeanCopyUtil<F, T> {
/**
* 源对象
*/
private final F from;
/**
* 目标对象
*/
private final T to;
/**
* 拷贝的字段信息列表
*/
private final List<BeanCopyField> copyFieldList = new LinkedList<>();
/**
* 配置信息
*/
private BeanCopyConfig config = new BeanCopyConfig();
private BeanCopyUtil(F from, T to) {
this.from = from;
this.to = to;
}
/**
* 指定需要拷贝的源对象和目标对象
*
* @param from 源对象
* @param to 目标对象
* @param <F> 源对象类型
* @param <T> 目标对象类型
* @return 一个 {@link BeanCopyUtil} 对象
*/
public static <F, T> BeanCopyUtil<F, T> copy(F from, T to) {
return new BeanCopyUtil<>(from, to);
}
/**
* 拷贝指定对象的字段
*
* @param fromField 源对象中的字段名
* @param toField 目标对象中的字段名
* @param converter 将源对象中字段转换为目标对象字段类型的转换器
* @return 返回 {@code this}
*/
public BeanCopyUtil<F, T> prop(String fromField, String toField, Function<? super Object, ? super Object> converter) {
copyFieldList.add(new BeanCopyField(fromField, toField, converter));
return this;
}
/**
* 拷贝指定对象的字段
*
* @param fromField 源对象中的字段名
* @param toField 目标对象中的字段名
* @return 返回 {@code this}
*/
public BeanCopyUtil<F, T> prop(String fromField, String toField) {
return prop(fromField, toField, null);
}
/**
* 拷贝指定对象的字段
*
* @param field 源对象中与目标对象中的字段名
* @param converter 将源对象中字段转换为目标对象字段类型的转换器
* @return 返回 {@code this}
*/
public BeanCopyUtil<F, T> prop(String field, Function<? super Object, ? super Object> converter) {
return prop(field, field, converter);
}
/**
* 拷贝指定对象的字段
*
* @param field 源对象中与目标对象中的字段名
* @return 返回 {@code this}
*/
public BeanCopyUtil<F, T> prop(String field) {
return prop(field, field, null);
}
/**
* 拷贝指定对象的多个字段
*
* @param fields 源对象中与目标对象中的多个字段名
* @return 返回 {@code this}
*/
public BeanCopyUtil<F, T> props(String... fields) {
for (String field : fields) {
prop(field);
}
return this;
}
/**
* 执行真正的拷贝操作
*
* @return 返回 {@code this}
*/
public BeanCopyUtil<F, T> exec() {
new BeanCopyOperator<>(from, to, copyFieldList, config).copy();
return this;
}
/**
* 重新开始添加其他对象的属性
* 用于在执行完 {@link #exec()} 之后还想复制其它对象的属性
*
* @param from 源对象
* @param <R> 源对象类型
* @return 一个新的 {@link BeanCopyUtil} 对象
*/
public <R> BeanCopyUtil<R, T> from(R from) {
return new BeanCopyUtil<>(from, to);
}
/**
* 返回当前的目标对象
*
* @return 当前的目标对象
*/
public T get() {
return to;
}
/**
* 配置拷贝的一些策略
*
* @param config 拷贝配置对象
* @return 返回 {@code this}
*/
public BeanCopyUtil<F, T> config(BeanCopyConfig config) {
this.config = config;
return this;
}
}
定义每个字段的操作类 BeanCopyField，保存对每个字段的操作
/**
* 拷贝属性的每一个字段的选项
*
* @author rxliuli
*/
public class BeanCopyField {
private String from;
private String to;
private Function<? super Object, ? super Object> converter;
public BeanCopyField() {
}
public BeanCopyField(String from, String to, Function<? super Object, ? super Object> converter) {
this.from = from;
this.to = to;
this.converter = converter;
}
public String getFrom() {
return from;
}
public BeanCopyField setFrom(String from) {
this.from = from;
return this;
}
public String getTo() {
return to;
}
public BeanCopyField setTo(String to) {
this.to = to;
return this;
}
public Function<? super Object, ? super Object> getConverter() {
return converter;
}
public BeanCopyField setConverter(Function<? super Object, ? super Object> converter) {
this.converter = converter;
return this;
}
}
定义 BeanCopyConfig，用于配置拷贝属性的策略
/**
* 拷贝属性的配置
*
* @author rxliuli
*/
public class BeanCopyConfig {
/**
* 同名的字段自动复制
*/
private boolean same = true;
/**
* 覆盖同名的字段
*/
private boolean override = true;
/**
* 忽略 {@code null} 的源对象属性
*/
private boolean ignoreNull = true;
/**
* 尝试进行自动转换
*/
private boolean converter = true;
public BeanCopyConfig() {
}
public BeanCopyConfig(boolean same, boolean override, boolean ignoreNull, boolean converter) {
this.same = same;
this.override = override;
this.ignoreNull = ignoreNull;
this.converter = converter;
}
public boolean isSame() {
return same;
}
public BeanCopyConfig setSame(boolean same) {
this.same = same;
return this;
}
public boolean isOverride() {
return override;
}
public BeanCopyConfig setOverride(boolean override) {
this.override = override;
return this;
}
public boolean isIgnoreNull() {
return ignoreNull;
}
public BeanCopyConfig setIgnoreNull(boolean ignoreNull) {
this.ignoreNull = ignoreNull;
return this;
}
public boolean isConverter() {
return converter;
}
public BeanCopyConfig setConverter(boolean converter) {
this.converter = converter;
return this;
}
}
定义 BeanCopyOperator 作为拷贝的真正实现
/**
* 真正执行 copy 属性的类
*
* @author rxliuli
*/
public class BeanCopyOperator<F, T> {
private static final Logger log = LoggerFactory.getLogger(BeanCopyUtil.class);
private final F from;
private final T to;
private final BeanCopyConfig config;
private List<BeanCopyField> copyFieldList;
public BeanCopyOperator(F from, T to, List<BeanCopyField> copyFieldList, BeanCopyConfig config) {
this.from = from;
this.to = to;
this.copyFieldList = copyFieldList;
this.config = config;
}
public void copy() {
//获取到两个对象所有的属性
final Map<String, Reflect> fromFields = Reflect.on(from).fields();
final Reflect to = Reflect.on(this.to);
final Map<String, Reflect> toFields = to.fields();
//过滤出所有相同字段名的字段并进行拷贝
if (config.isSame()) {
final Map<ListUtil.ListDiffState, List<String>> different = ListUtil.different(new ArrayList<>(fromFields.keySet()), new ArrayList<>(toFields.keySet()));
copyFieldList = Stream.concat(different.get(ListUtil.ListDiffState.common).stream()
.map(s -> new BeanCopyField(s, s, null)), copyFieldList.stream())
.collect(Collectors.toList());
}
//根据拷贝字段列表进行拷贝
copyFieldList.stream()
//忽略空值
.filter(beanCopyField -> !config.isIgnoreNull() || fromFields.get(beanCopyField.getFrom()).get() != null)
//覆盖属性
.filter(beanCopyField -> config.isOverride() || toFields.get(beanCopyField.getTo()).get() == null)
//如果没有转换器，则使用默认的转换器
.peek(beanCopyField -> {
if (beanCopyField.getConverter() == null) {
beanCopyField.setConverter(Function.identity());
}
})
.forEach(beanCopyField -> {
final String fromField = beanCopyField.getFrom();
final F from = fromFields.get(fromField).get();
final String toField = beanCopyField.getTo();
try {
to.set(toField, beanCopyField.getConverter().apply(from));
} catch (ReflectException e) {
log.warn("Copy field failed, from {} to {}, exception is {}", fromField, toField, e.getMessage());
}
});
}
}
使用
使用流程图
测试
代码写完了，让我们测试一下！
public class BeanCopyUtilTest {
private final Logger log = LoggerFactory.getLogger(getClass());
private Student student;
private Teacher teacher;
@Before
public void before() {
student = new Student("琉璃", 10, "女", 4);
teacher = new Teacher();
}
@Test
public void copy() {
//简单的复制（类似于 BeanUtils.copyProperties）
BeanCopyUtil.copy(student, teacher).exec();
log.info("teacher: {}", teacher);
assertThat(teacher)
.extracting("age")
.containsOnlyOnce(student.getAge());
}
@Test
public void prop() {
//不同名字的属性
BeanCopyUtil.copy(student, teacher)
.prop("sex", "sex", sex -> Objects.equals(sex, "男"))
.prop("realname", "name")
.exec();
assertThat(teacher)
.extracting("name", "age", "sex")
.containsOnlyOnce(student.getRealname(), student.getAge(), false);
}
@Test
public void prop1() {
//不存的属性
assertThat(BeanCopyUtil.copy(student, teacher)
.prop("sex", "sex", sex -> Objects.equals(sex, "男"))
.prop("realname", "name2")
.exec()
.get())
.extracting("age", "sex")
.containsOnlyOnce(student.getAge(), false);
}
@Test
public void from() {
final Teacher lingMeng = new Teacher()
.setName("灵梦")
.setAge(17);
//测试 from 是否覆盖
assertThat(BeanCopyUtil.copy(student, teacher)
.prop("sex", "sex", sex -> Objects.equals(sex, "男"))
.prop("realname", "name")
.exec()
.from(lingMeng)
.exec()
.get())
.extracting("name", "age", "sex")
.containsOnlyOnce(lingMeng.getName(), lingMeng.getAge(), false);
}
@Test
public void get() {
//测试 get 是否有效
assertThat(BeanCopyUtil.copy(student, teacher)
.prop("sex", "sex", sex -> Objects.equals(sex, "男"))
.prop("realname", "name")
.exec()
.get())
.extracting("name", "age", "sex")
.containsOnlyOnce(student.getRealname(), student.getAge(), false);
}
@Test
public void config() {
//不自动复制同名属性
assertThat(BeanCopyUtil.copy(new Student().setAge(15), new Teacher())
.config(new BeanCopyConfig().setSame(false))
.exec()
.get())
.extracting("age")
.containsOnlyNulls();
//不覆盖不为空的属性
assertThat(BeanCopyUtil.copy(new Student().setAge(15), new Teacher().setAge(10))
.config(new BeanCopyConfig().setOverride(false))
.exec()
.get())
.extracting("age")
.containsOnlyOnce(10);
//不忽略源对象不为空的属性
assertThat(BeanCopyUtil.copy(new Student(), student)
.config(new BeanCopyConfig().setIgnoreNull(false))
.exec()
.get())
.extracting("realname", "age", "sex", "grade")
.containsOnlyNulls();
}
/**
* 测试学生类
*/
private static class Student {
/**
* 姓名
*/
private String realname;
/**
* 年龄
*/
private Integer age;
/**
* 性别，男/女
*/
private String sex;
/**
* 年级，1 - 6
*/
private Integer grade;
public Student() {
}
public Student(String realname, Integer age, String sex, Integer grade) {
this.realname = realname;
this.age = age;
this.sex = sex;
this.grade = grade;
}
public String getRealname() {
return realname;
}
public Student setRealname(String realname) {
this.realname = realname;
return this;
}
public Integer getAge() {
return age;
}
public Student setAge(Integer age) {
this.age = age;
return this;
}
public String getSex() {
return sex;
}
public Student setSex(String sex) {
this.sex = sex;
return this;
}
public Integer getGrade() {
return grade;
}
public Student setGrade(Integer grade) {
this.grade = grade;
return this;
}
@Override
public String toString() {
return ToStringBuilder.reflectionToString(this);
}
}
/**
* 测试教师类
*/
private static class Teacher {
/**
* 姓名
*/
private String name;
/**
* 年龄
*/
private Integer age;
/**
* 性别，true 男，false 女
*/
private Boolean sex;
/**
* 职位
*/
private String post;
public Teacher() {
}
public Teacher(String name, Integer age, Boolean sex, String post) {
this.name = name;
this.age = age;
this.sex = sex;
this.post = post;
}
public String getName() {
return name;
}
public Teacher setName(String name) {
this.name = name;
return this;
}
public Integer getAge() {
return age;
}
public Teacher setAge(Integer age) {
this.age = age;
return this;
}
public Boolean getSex() {
return sex;
}
public Teacher setSex(Boolean sex) {
this.sex = sex;
return this;
}
public String getPost() {
return post;
}
public Teacher setPost(String post) {
this.post = post;
return this;
}
@Override
public String toString() {
return ToStringBuilder.reflectionToString(this);
}
}
}
如果没有发生什么意外，那么一切将能够正常运行！
好了，那么关于在 Java 中优雅的拷贝对象属性就到这里啦
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