BeanUtils

Mon, 01 Jan 0001 00:00:00 +0000

BeanUtils

copyProperties

以下是针对相同类型的 Bean 处理的例子：

public class CopyPropsToSameType {

 public static void main(String[] args) {
 BeanWrapper bw = new BeanWrapperImpl(new TestBean());
 bw.setPropertyValue("aString", "someString");
 bw.setPropertyValue("anInt", 3);

 TestBean testBean2 = new TestBean();

 BeanUtils.copyProperties(bw.getWrappedInstance(), testBean2);

 System.out.println(testBean2);
 }
}
// TestBean{aString='someString', anInt=3, date=Mon May 01 16:08:07 CDT 2017}

以下是针对不同类型的 Bean 处理的例子：

public class CopyPropsToDifferentType {

 public static void main(String[] args) {
 BeanWrapper bw = new BeanWrapperImpl(new TestBean());
 bw.setPropertyValue("aString", "someString");
 bw.setPropertyValue("anInt", 3);

 TestBeanDifferent testBean2 = new TestBeanDifferent();

 //only properties of same name will be copied
 BeanUtils.copyProperties(bw.getWrappedInstance(), testBean2);

 System.out.println(testBean2);
 }

 private static class TestBeanDifferent {
 private String aString;
 private int differentInt;

 public String getAString() {
 return aString;
 }

 public void setAString(String aString) {
 this.aString = aString;
 }

 public int getDifferentInt() {
 return differentInt;
 }

 public void setDifferentInt(int differentInt) {
 this.differentInt = differentInt;
 }

 @Override
 public String toString() {
 return (
 "TestBeanDifferent{" +
 "aString='" +
 aString +
 '\'' +
 ", differentInt=" +
 differentInt +
 '}'
 );
 }
 }
}
// TestBeanDifferent{aString='someString', differentInt=0}

getPropertyDescriptors

public class PropDescriptorExample {

 public static void main(String[] args) throws IntrospectionException {
 PropertyDescriptor[] actual = Introspector
 .getBeanInfo(TestBean.class)
 .getPropertyDescriptors();
 PropertyDescriptor[] descriptors = BeanUtils.getPropertyDescriptors(
 TestBean.class
 );

 System.out.println(Arrays.toString(actual));
 System.out.println(Arrays.toString(descriptors));
 }
}
// [java.beans.PropertyDescriptor[name=AString; propertyType=class java.lang.String; readMethod=public java.lang.String com.logicbig.example.TestBean.getAString(); writeMethod=public void com.logicbig.example.TestBean.setAString(java.lang.String)], java.beans.PropertyDescriptor[name=anInt; propertyType=int; readMethod=public int com.logicbig.example.TestBean.getAnInt(); writeMethod=public void com.logicbig.example.TestBean.setAnInt(int)], java.beans.PropertyDescriptor[name=class; propertyType=class java.lang.Class; readMethod=public final native java.lang.Class java.lang.Object.getClass()], java.beans.PropertyDescriptor[name=date; propertyType=class java.util.Date; readMethod=public java.util.Date com.logicbig.example.TestBean.getDate()]]

resolveSignature

public class ResolveSignature {

 public static void main(String[] args)
 throws InvocationTargetException, IllegalAccessException {
 Method doSomething = BeanUtils.resolveSignature(
 "aMethod(java.lang.String, int)",
 LocalBean.class
 );
 doSomething.invoke(new LocalBean(), "some string value", 100);

 doSomething =
 BeanUtils.resolveSignature("aMethod(java.lang.Integer)", LocalBean.class);
 doSomething.invoke(new LocalBean(), 200);
 }

 private static class LocalBean {

 public void aMethod(String str, int anInt) {
 System.out.println(str);
 System.out.println(anInt);
 }

 public void aMethod(Integer anInt) {
 System.out.println(anInt);
 }
 }
}

/**
 some string value
 100
 200
*/
public class ResolveSignature2 {

 public static void main(String[] args)
 throws InvocationTargetException, IllegalAccessException {
 Method doSomething = BeanUtils.resolveSignature(
 "doSomething",
 LocalBean.class
 );
 doSomething.invoke(new LocalBean());
 }

 private static class LocalBean {

 public void doSomething() {
 System.out.println("-- doing something -- ");
 }
 }
}
// -- doing something --

copyProperties

Mon, 01 Jan 0001 00:00:00 +0000

copyProperties

copyProperties 是 Spring BeanUtils 工具箱中提供的用于 Bean 之间属性复制的方法。

package com.abc.demo;

import java.util.Arrays;
import java.util.List;
import org.springframework.beans.BeanUtils;

public class Main {

 public static void main(String[] args) {
 List<Article> articleList = Arrays.asList(new Article(1L, "hello world"));

 Member m1 = new Member("Eddy", articleList);
 Member m2 = new Member();
 BeanUtils.copyProperties(m1, m2);

 System.out.println("m1:" + m1); // m1:name:Eddy, articleList:[id:1, content:hello world]
 System.out.println("m2:" + m2); // m2:name:Eddy, articleList:[id:1, content:hello world]
 }
}

class Member {
 private String name;
 private List<Article> articleList;

 public Member() {}

 public Member(String name, List<Article> articleList) {
 this.name = name;
 this.articleList = articleList;
 }

 @Override
 public String toString() {
 return "name:" + name + ", " + "articleList:" + articleList;
 }
// getters and setters
}

class Article {
 private Long id;
 private String content;

 public Article(Long id, String content) {
 this.id = id;
 this.content = content;
 }

 @Override
 public String toString() {
 return "id:" + id + ", content:" + content;
 }
// getters and setters
}

上面可以看到经由BeanUtils.copyProperties()复制后m2的属性值确实与m1相同，里面的List物件属性也会被复制，属于深拷贝(deep copy)。下面范例则是把m1复制到另一个类别User，除了articlelist属性名称外几乎相同。

package com.abc.demo;

import java.util.Arrays;
import java.util.List;
import org.springframework.beans.BeanUtils;

public class Main {

 public static void main(String[] args) {
 List<Article> articleList = Arrays.asList(new Article(1L, "hello world"));

 Member m1 = new Member("Eddy", articleList);

 User u1 = new User();
 BeanUtils.copyProperties(m1, u1);

 System.out.println("m1:" + m1); // m1:name:Eddy, articleList:[id:1, content:hello world]
 System.out.println("u1:" + u1); // u1:name:Eddy, articlelist:null
 }
}

class Member {
 private String name;
 private List<Article> articleList; // <-- small camel case

 public Member() {}

 public Member(String name, List<Article> articleList) {
 this.name = name;
 this.articleList = articleList;
 }

 @Override
 public String toString() {
 return "name:" + name + ", " + "articleList:" + articleList;
 }
// getters and setters
}

class Article {
 private Long id;
 private String content;

 public Article(Long id, String content) {
 this.id = id;
 this.content = content;
 }

 @Override
 public String toString() {
 return "id:" + id + ", content:" + content;
 }
// getters and setters
}

class User {
 private String name;
 private String articlelist; // <-- all lowercase

 public String getName() {
 return name;
 }

 @Override
 public String toString() {
 return "name:" + name + ", " + "articleList:" + articlelist;
 }
// getters and setters
}

此时 u1.articlelist 的内容却是 null，由此可知 BeanUtils.copyProperties()只会复制属性名称相同的属性值，若属性名称不同则被忽略。

内部实现

BeanUtils.copyProperties()是利用 Java 的反射 reflection 来达成，以下是原始码。

public abstract class BeanUtils {
 ...
 private static void copyProperties(Object source, Object target, @Nullable Class<?> editable,
 @Nullable String... ignoreProperties) throws BeansException {

 Assert.notNull(source, "Source must not be null");
 Assert.notNull(target, "Target must not be null");

 Class<?> actualEditable = target.getClass();
 if (editable != null) {
 if (!editable.isInstance(target)) {
 throw new IllegalArgumentException("Target class [" + target.getClass().getName() +
 "] not assignable to Editable class [" + editable.getName() + "]");
 }
 actualEditable = editable;
 }
 PropertyDescriptor[] targetPds = getPropertyDescriptors(actualEditable);
 List<String> ignoreList = (ignoreProperties != null ? Arrays.asList(ignoreProperties) : null);

 for (PropertyDescriptor targetPd : targetPds) {
 Method writeMethod = targetPd.getWriteMethod();
 if (writeMethod != null && (ignoreList == null || !ignoreList.contains(targetPd.getName()))) {
 PropertyDescriptor sourcePd = getPropertyDescriptor(source.getClass(), targetPd.getName()); // 以目的對象(target)的屬性名稱來取得來源對象(source)的屬性
 if (sourcePd != null) {
 Method readMethod = sourcePd.getReadMethod();
 if (readMethod != null &&
 ClassUtils.isAssignable(writeMethod.getParameterTypes()[0], readMethod.getReturnType())) {
 try {
 if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers())) {
 readMethod.setAccessible(true);
 }
 Object value = readMethod.invoke(source); // 取得來源對象的屬性值
 if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers())) {
 writeMethod.setAccessible(true);
 }
 writeMethod.invoke(target, value); // 把來源對象的屬性值寫入目的對象的同名屬性
 }
 catch (Throwable ex) {
 throw new FatalBeanException(
 "Could not copy property '" + targetPd.getName() + "' from source to target", ex);
 }
 }
 }
 }
 }
 }
 ...
}

BeanUtils.copyProperties()虽然在复制 POJO 物件时非常方便，但在属性的命名上必须统一，所以系统中各属性的命名规则必须严格规范。还有个问题就是 debug 时错误不好找，所以并不推荐使用。大型程序中最好有专人专职负责维护整个系统的命名列表，中英文对照表，名词解释等，让开发人员可以直接查找使用，如果找不到就写信去申请由维护人员建立，否则就常看到同一种东西在程序中出现多种名称，这样 BeanUtils.copyProperties()就派不上用场了，更严重的是维护上常令人困惑。

例如顾客编号 customerId，customerID，custId，custID，clientId，clientId；
商品数量 quantity, qty；
利息收入 interestIncome，intstIncome，intrstIncome，intstRevenue；
一次性费用 onetimeExpense，onceExpense，oneExpense 等。

7.Spring 工具库 | Next-gen Tech Edu

BeanUtils

BeanUtils

copyProperties

getPropertyDescriptors

resolveSignature

copyProperties

copyProperties

内部实现