在我們實(shí)際項(xiàng)目開(kāi)發(fā)過(guò)程中，我們經(jīng)常需要將不同的兩個(gè)對(duì)象實(shí)例進(jìn)行屬性復(fù)制，從而基于源對(duì)象的屬性信息進(jìn)行后續(xù)操作，而不改變?cè)磳?duì)象的屬性信息,比如DTO數(shù)據(jù)傳輸對(duì)象和數(shù)據(jù)對(duì)象DO，我們需要將DO對(duì)象進(jìn)行屬性復(fù)制到DTO，但是對(duì)象格式又不一樣，所以我們需要編寫(xiě)映射代碼將對(duì)象中的屬性值從一種類型轉(zhuǎn)換成另一種類型。

這種轉(zhuǎn)換最原始的方式就是手動(dòng)編寫(xiě)大量的 get/set代碼，當(dāng)然這是我們開(kāi)發(fā)過(guò)程不愿意去做的，因?yàn)樗_實(shí)顯得很繁瑣。為了解決這一痛點(diǎn)，就誕生了一些方便的類庫(kù)，常用的有 apache的 BeanUtils,spring的 BeanUtils, Dozer,Orika等拷貝工具。這篇文章主要介紹 Apache的BeanUtils 與 Spring 的BeanUtils，其他框架后續(xù)文章再做介紹

對(duì)象拷貝

在具體介紹兩種 BeanUtils之前，先來(lái)補(bǔ)充一些基礎(chǔ)知識(shí)。它們兩種工具本質(zhì)上就是對(duì)象拷貝工具，而對(duì)象拷貝又分為深拷貝和淺拷貝，下面進(jìn)行詳細(xì)解釋。

什么是淺拷貝和深拷貝

在Java中，除了 基本數(shù)據(jù)類型之外，還存在 類的實(shí)例對(duì)象這個(gè)引用數(shù)據(jù)類型，而一般使用 “=”號(hào)做賦值操作的時(shí)候，對(duì)于基本數(shù)據(jù)類型，實(shí)際上是拷貝的它的值，但是對(duì)于對(duì)象而言，其實(shí)賦值的只是這個(gè)對(duì)象的引用，將原對(duì)象的引用傳遞過(guò)去，他們實(shí)際還是指向的同一個(gè)對(duì)象。

而淺拷貝和深拷貝就是在這個(gè)基礎(chǔ)上做的區(qū)分，如果在拷貝這個(gè)對(duì)象的時(shí)候，只對(duì)基本數(shù)據(jù)類型進(jìn)行了拷貝，而對(duì)引用數(shù)據(jù)類型只是進(jìn)行引用的傳遞，而沒(méi)有真實(shí)的創(chuàng)建一個(gè)新的對(duì)象，則認(rèn)為是淺拷貝。反之，在對(duì)引用數(shù)據(jù)類型進(jìn)行拷貝的時(shí)候，創(chuàng)建了一個(gè)新的對(duì)象，并且復(fù)制其內(nèi)的成員變量，則認(rèn)為是深拷貝。

簡(jiǎn)單來(lái)說(shuō):

• 淺拷貝：對(duì)基本數(shù)據(jù)類型進(jìn)行值傳遞，對(duì)引用數(shù)據(jù)類型進(jìn)行引用傳遞般的拷貝，此為淺拷貝
• 深拷貝：對(duì)基本數(shù)據(jù)類型進(jìn)行值傳遞，對(duì)引用數(shù)據(jù)類型，創(chuàng)建一個(gè)新的對(duì)象，并復(fù)制其內(nèi)容，此為深拷貝。

BeanUtils

前面簡(jiǎn)單講了一下對(duì)象拷貝的一些知識(shí)，下面就來(lái)具體看下兩種BeanUtils工具

Apache 的 BeanUtils

首先來(lái)看一個(gè)非常簡(jiǎn)單的BeanUtils的例子

public?class?PersonSource??{
????private?Integer?id;
????private?String?username;
????private?String?password;
????private?Integer?age;
????//?getters/setters?omiited
}
public?class?PersonDest?{
????private?Integer?id;
????private?String?username;
????private?Integer?age;
????//?getters/setters?omiited
}
public?class?TestApacheBeanUtils?{
????public?static?void?main(String[]?args)?throws?InvocationTargetException,?IllegalAccessException?{
???????//下面只是用于單獨(dú)測(cè)試
????????PersonSource?personSource?=?new?PersonSource(1,?"pjmike",?"12345",?21);
????????PersonDest?personDest?=?new?PersonDest();
????????BeanUtils.copyProperties(personDest,personSource);
????????System.out.println("persondest:?"+personDest);
????}
}
persondest:?PersonDest{id=1,?username='pjmike',?age=21}

從上面的例子可以看出，對(duì)象拷貝非常簡(jiǎn)單，BeanUtils最常用的方法就是:

//將源對(duì)象中的值拷貝到目標(biāo)對(duì)象
public?static?void?copyProperties(Object?dest,?Object?orig)?throws?IllegalAccessException,?InvocationTargetException?{
????BeanUtilsBean.getInstance().copyProperties(dest,?orig);
}

默認(rèn)情況下，使用org.apache.commons.beanutils.BeanUtils對(duì)復(fù)雜對(duì)象的復(fù)制是引用，這是一種淺拷貝

但是由于 Apache下的BeanUtils對(duì)象拷貝性能太差，不建議使用，而且在阿里巴巴Java開(kāi)發(fā)規(guī)約也明確指出：

“

避免用Apache Beanutils進(jìn)行屬性的copy。

commons-beantutils 對(duì)于對(duì)象拷貝加了很多的檢驗(yàn)，包括類型的轉(zhuǎn)換，甚至還會(huì)檢驗(yàn)對(duì)象所屬的類的可訪問(wèn)性,可謂相當(dāng)復(fù)雜，這也造就了它的差勁的性能，具體實(shí)現(xiàn)代碼如下：

public?void?copyProperties(final?Object?dest,?final?Object?orig)
????????throws?IllegalAccessException,?InvocationTargetException?{

????????//?Validate?existence?of?the?specified?beans
????????if?(dest?==?null)?{
????????????throw?new?IllegalArgumentException
????????????????????("No?destination?bean?specified");
????????}
????????if?(orig?==?null)?{
????????????throw?new?IllegalArgumentException("No?origin?bean?specified");
????????}
????????if?(log.isDebugEnabled())?{
????????????log.debug("BeanUtils.copyProperties("?+?dest?+?",?"?+
??????????????????????orig?+?")");
????????}

????????//?Copy?the?properties,?converting?as?necessary
????????if?(orig?instanceof?DynaBean)?{
????????????final?DynaProperty[]?origDescriptors?=
????????????????((DynaBean)?orig).getDynaClass().getDynaProperties();
????????????for?(DynaProperty?origDescriptor?:?origDescriptors)?{
????????????????final?String?name?=?origDescriptor.getName();
????????????????//?Need?to?check?isReadable()?for?WrapDynaBean
????????????????//?(see?Jira?issue#?BEANUTILS-61)
????????????????if?(getPropertyUtils().isReadable(orig,?name)?&&
????????????????????getPropertyUtils().isWriteable(dest,?name))?{
????????????????????final?Object?value?=?((DynaBean)?orig).get(name);
????????????????????copyProperty(dest,?name,?value);
????????????????}
????????????}
????????}?else?if?(orig?instanceof?Map)?{
????????????@SuppressWarnings("unchecked")
????????????final
????????????//?Map?properties?are?always?of?type?
????????????Map?propMap?=?(Map)?orig;
????????????for?(final?Map.Entry?entry?:?propMap.entrySet())?{
????????????????final?String?name?=?entry.getKey();
????????????????if?(getPropertyUtils().isWriteable(dest,?name))?{
????????????????????copyProperty(dest,?name,?entry.getValue());
????????????????}
????????????}
????????}?else?/*?if?(orig?is?a?standard?JavaBean)?*/?{
????????????final?PropertyDescriptor[]?origDescriptors?=
????????????????getPropertyUtils().getPropertyDescriptors(orig);
????????????for?(PropertyDescriptor?origDescriptor?:?origDescriptors)?{
????????????????final?String?name?=?origDescriptor.getName();
????????????????if?("class".equals(name))?{
????????????????????continue;?//?No?point?in?trying?to?set?an?object's?class
????????????????}
????????????????if?(getPropertyUtils().isReadable(orig,?name)?&&
????????????????????getPropertyUtils().isWriteable(dest,?name))?{
????????????????????try?{
????????????????????????final?Object?value?=
????????????????????????????getPropertyUtils().getSimpleProperty(orig,?name);
????????????????????????copyProperty(dest,?name,?value);
????????????????????}?catch?(final?NoSuchMethodException?e)?{
????????????????????????//?Should?not?happen
????????????????????}
????????????????}
????????????}
????????}

????}

Spring的 BeanUtils

使用spring的BeanUtils進(jìn)行對(duì)象拷貝:

public?class?TestSpringBeanUtils?{
????public?static?void?main(String[]?args)?throws?InvocationTargetException,?IllegalAccessException?{

???????//下面只是用于單獨(dú)測(cè)試
????????PersonSource?personSource?=?new?PersonSource(1,?"pjmike",?"12345",?21);
????????PersonDest?personDest?=?new?PersonDest();
????????BeanUtils.copyProperties(personSource,personDest);
????????System.out.println("persondest:?"+personDest);
????}
}

spring下的BeanUtils也是使用 copyProperties方法進(jìn)行拷貝，只不過(guò)它的實(shí)現(xiàn)方式非常簡(jiǎn)單，就是對(duì)兩個(gè)對(duì)象中相同名字的屬性進(jìn)行簡(jiǎn)單的get/set，僅檢查屬性的可訪問(wèn)性。具體實(shí)現(xiàn)如下:

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?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());
????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);
???????if?(!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers()))?{
????????writeMethod.setAccessible(true);
???????}
???????writeMethod.invoke(target,?value);
??????}
??????catch?(Throwable?ex)?{
???????throw?new?FatalBeanException(
?????????"Could?not?copy?property?'"?+?targetPd.getName()?+?"'?from?source?to?target",?ex);
??????}
?????}
????}
???}
??}
?}

可以看到，成員變量賦值是基于目標(biāo)對(duì)象的成員列表，并且會(huì)跳過(guò)ignore的以及在源對(duì)象中不存在，所以這個(gè)方法是安全的，不會(huì)因?yàn)閮蓚€(gè)對(duì)象之間的結(jié)構(gòu)差異導(dǎo)致錯(cuò)誤，但是必須保證同名的兩個(gè)成員變量類型相同

小結(jié)

以上簡(jiǎn)要的分析兩種BeanUtils，因?yàn)锳pache下的BeanUtils性能較差，不建議使用，可以使用 Spring的BeanUtils,或者使用其他拷貝框架，比如 cglib BeanCopier,基于javassist的Orika等，這些也是非常優(yōu)秀的類庫(kù)，值得去嘗試。