Java对象复制系列二: 手把手带你写一个Apache BeanUtils

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前言

Apache BeanUtils 是Java中用来复制2个对象属性的一个类型。

上一篇文章我们讲到了 Apache BeanUtils 性能相对比较差，今天我不仅仅要带你学习源代码 ，更要带你手把手写一个Apache BeanUtils。

最佳实践

直接上案例

案例地址： https://github.com/zhuangjiaju/easytools/blob/main/easytools-test/src/test/java/com/github/zhuangjiaju/easytools/test/demo/beanutils/ApacheBeanUtilsTest.java

简单的复制对象

直接上代码：

创建一个java 对象：

/*** Apache BeanUtils 使用的demo*/
@Test
public void demo() throws Exception {BeanUtilsDemoDTO beanUtilsDemo = new BeanUtilsDemoDTO();beanUtilsDemo.setId("id");beanUtilsDemo.setFirstName("firstName");BeanUtilsDemoDTO newBeanUtilsDemo = new BeanUtilsDemoDTO();BeanUtils.copyProperties(newBeanUtilsDemo, beanUtilsDemo);log.info("newBeanUtilsDemo: {}", newBeanUtilsDemo);
}

输出结果:

     20:21:56.949 [main] INFO com.github.zhuangjiaju.easytools.test.demo.beanutils.ApacheBeanUtilsTest -- newBeanUtilsDemo: BeanUtilsDemoDTO(id=id, firstName=firstName, lastName=null, age=null, email=null, phoneNumber=null, address=null, city=null, state=null, country=null, major=null, gpa=null, department=null, yearOfStudy=null, advisorName=null, enrollmentStatus=null, dormitoryName=null, roommateName=null, scholarshipDetails=null, extracurricularActivities=null)

可见已经复制对象成功了，输出里面有 firstName 的值。

直接自己写一个简单的 BeanUtils

源码有点复杂，我先直接写一个简单的 BeanUtils，非常的通俗易懂，看懂了然后再看源代码就非常容易了。

复制的代码一模一样：

/*** 自己写一个简单的 BeanUtils*/
@Test
public void custom() throws Exception {BeanUtilsDemoDTO beanUtilsDemo = new BeanUtilsDemoDTO();beanUtilsDemo.setId("id");beanUtilsDemo.setFirstName("firstName");BeanUtilsDemoDTO newBeanUtilsDemo = new BeanUtilsDemoDTO();MyBeanUtils.copyProperties(newBeanUtilsDemo, beanUtilsDemo);log.info("newBeanUtilsDemo: {}", newBeanUtilsDemo);
}

我们自己实现的工具类：

前置知识：

Introspector.getBeanInfo： 是 Java 自带的一个类，可以获取一个类的 BeanInfo 信息，然后获取属性的描述资料 PropertyDescriptor
BeanInfo ： bean 的描述信息
PropertyDescriptor： bean 的属性的资料信息 ，可以获取到属性的 get/set 方法
Method： 方法,用这个对象可以反射掉调用

 public static class MyBeanUtils {/*** 复制方法** @param dest* @param orig* @throws Exception*/public static void copyProperties(Object dest, Object orig) throws Exception {// 获取目标对象的 PropertyDescriptor 属性资料PropertyDescriptor[] destPropertyDescriptors = Introspector.getBeanInfo(dest.getClass(), Object.class).getPropertyDescriptors();// 获取来源对象的 PropertyDescriptor 属性资料PropertyDescriptor[] origPropertyDescriptors = Introspector.getBeanInfo(orig.getClass(), Object.class).getPropertyDescriptors();// 上面2个 在 Apache BeanUtils 还加了缓存// 循环目标对象for (PropertyDescriptor propertyDescriptor : destPropertyDescriptors) {// 获取属性名String name = propertyDescriptor.getName();// 循环来源对象的属性名for (PropertyDescriptor origPropertyDescriptor : origPropertyDescriptors) {// 2个属性名匹配上了if (name.equals(origPropertyDescriptor.getName())) {// 直接获取 method 然后反色调用即可 就设置了数据propertyDescriptor.getWriteMethod().invoke(dest,origPropertyDescriptor.getReadMethod().invoke(orig));break;}}}}
}

代码是不是非常的容易？就是循环目标对象的属性，然后循环来源对象的属性，然后匹配上了就反射调用即可。

和 Apache BeanUtils 的源码逻辑基本一样，只是没有加缓存之类的。

源码解析

org.apache.commons.beanutils.BeanUtils.copyProperties

public static void copyProperties(final Object dest, final Object orig)throws IllegalAccessException, InvocationTargetException {// BeanUtilsBean 放在了 ThreadLocal 里面，所以是不可以并发的，但是通过 ThreadLocal 保障了BeanUtilsBean不会并发 也不会每次都new // 直接调用 copyPropertiesBeanUtilsBean.getInstance().copyProperties(dest, orig);
}

org.apache.commons.beanutils.BeanUtilsBean.copyProperties

 public void copyProperties(final Object dest, final Object orig)throws IllegalAccessException, InvocationTargetException {// Validate existence of the specified beansif (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 necessaryif (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 <String, Object>Map<String, Object> propMap = (Map<String, Object>)orig;for (final Map.Entry<String, Object> 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) */ {// 这里比较核心 获取来源的PropertyDescriptor 属性资料 和我们自己实现的代码 一样// getPropertyDescriptors 我们会继续跟进final PropertyDescriptor[] origDescriptors =getPropertyUtils().getPropertyDescriptors(orig);// 循环来源的 属性资料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);// 调用复制参数 // copyProperty 我们会继续跟进copyProperty(dest, name, value);} catch (final NoSuchMethodException e) {// Should not happen}}}}}

org.apache.commons.beanutils.PropertyUtilsBean.getPropertyDescriptors(java.lang.Object)
org.apache.commons.beanutils.PropertyUtilsBean.getPropertyDescriptors(java.lang.Class<?>)
org.apache.commons.beanutils.PropertyUtilsBean.getIntrospectionData

  private BeanIntrospectionData getIntrospectionData(final Class<?> beanClass) {if (beanClass == null) {throw new IllegalArgumentException("No bean class specified");}// Look up any cached information for this bean class// 和我们自己写的比，这里核心是加了一个descriptorsCache 的缓存 BeanIntrospectionData data = descriptorsCache.get(beanClass);if (data == null) {data = fetchIntrospectionData(beanClass);descriptorsCache.put(beanClass, data);}return data;
}

org.apache.commons.beanutils.PropertyUtilsBean.fetchIntrospectionData
org.apache.commons.beanutils.DefaultBeanIntrospector.introspect

 public void introspect(final IntrospectionContext icontext) {BeanInfo beanInfo = null;try {// 这里和我们自己实现的一样 可以获取一个类的 BeanInfo 信息beanInfo = Introspector.getBeanInfo(icontext.getTargetClass());} catch (final IntrospectionException e) {// no descriptors are added to the contextlog.error("Error when inspecting class " + icontext.getTargetClass(),e);return;}//  获取 bean 的 PropertyDescriptor 属性的资料信息PropertyDescriptor[] descriptors = beanInfo.getPropertyDescriptors();if (descriptors == null) {descriptors = new PropertyDescriptor[0];}handleIndexedPropertyDescriptors(icontext.getTargetClass(),descriptors);icontext.addPropertyDescriptors(descriptors);
}

通过以上方法，我们就拿到了 PropertyDescriptor[] origDescriptors 接下来我们看 copyProperty

org.apache.commons.beanutils.BeanUtilsBean.copyProperty

public void copyProperty(final Object bean, String name, Object value)throws IllegalAccessException, InvocationTargetException {// Trace logging (if enabled)if (log.isTraceEnabled()) {final StringBuilder sb = new StringBuilder("  copyProperty(");sb.append(bean);sb.append(", ");sb.append(name);sb.append(", ");if (value == null) {sb.append("<NULL>");} else if (value instanceof String) {sb.append((String)value);} else if (value instanceof String[]) {final String[] values = (String[])value;sb.append('[');for (int i = 0; i < values.length; i++) {if (i > 0) {sb.append(',');}sb.append(values[i]);}sb.append(']');} else {sb.append(value.toString());}sb.append(')');log.trace(sb.toString());}// Resolve any nested expression to get the actual target beanObject target = bean;final Resolver resolver = getPropertyUtils().getResolver();while (resolver.hasNested(name)) {try {target = getPropertyUtils().getProperty(target, resolver.next(name));name = resolver.remove(name);} catch (final NoSuchMethodException e) {return; // Skip this property setter}}if (log.isTraceEnabled()) {log.trace("    Target bean = " + target);log.trace("    Target name = " + name);}// Declare local variables we will requirefinal String propName = resolver.getProperty(name); // Simple name of target propertyClass<?> type = null;                         // Java type of target propertyfinal int index = resolver.getIndex(name);         // Indexed subscript value (if any)final String key = resolver.getKey(name);           // Mapped key value (if any)// Calculate the target property typeif (target instanceof DynaBean) {final DynaClass dynaClass = ((DynaBean)target).getDynaClass();final DynaProperty dynaProperty = dynaClass.getDynaProperty(propName);if (dynaProperty == null) {return; // Skip this property setter}type = dynaPropertyType(dynaProperty, value);} else {PropertyDescriptor descriptor = null;try {descriptor =getPropertyUtils().getPropertyDescriptor(target, name);if (descriptor == null) {return; // Skip this property setter}} catch (final NoSuchMethodException e) {return; // Skip this property setter}type = descriptor.getPropertyType();if (type == null) {// Most likely an indexed setter on a POJB onlyif (log.isTraceEnabled()) {log.trace("    target type for property '" +propName + "' is null, so skipping ths setter");}return;}}if (log.isTraceEnabled()) {log.trace("    target propName=" + propName + ", type=" +type + ", index=" + index + ", key=" + key);}// Convert the specified value to the required type and store itif (index >= 0) {                    // Destination must be indexedvalue = convertForCopy(value, type.getComponentType());try {getPropertyUtils().setIndexedProperty(target, propName,index, value);} catch (final NoSuchMethodException e) {throw new InvocationTargetException(e, "Cannot set " + propName);}} else if (key != null) {            // Destination must be mapped// Maps do not know what the preferred data type is,// so perform no conversions at all// FIXME - should we create or support a TypedMap?try {getPropertyUtils().setMappedProperty(target, propName,key, value);} catch (final NoSuchMethodException e) {throw new InvocationTargetException(e, "Cannot set " + propName);}} else {                             // Destination must be simplevalue = convertForCopy(value, type);try {// 核心我们看这里 设置属性值getPropertyUtils().setSimpleProperty(target, propName, value);} catch (final NoSuchMethodException e) {throw new InvocationTargetException(e, "Cannot set " + propName);}}}

org.apache.commons.beanutils.PropertyUtilsBean.setSimpleProperty

public void setSimpleProperty(final Object bean,final String name, final Object value)throws IllegalAccessException, InvocationTargetException,NoSuchMethodException {if (bean == null) {throw new IllegalArgumentException("No bean specified");}if (name == null) {throw new IllegalArgumentException("No name specified for bean class '" +bean.getClass() + "'");}// Validate the syntax of the property nameif (resolver.hasNested(name)) {throw new IllegalArgumentException("Nested property names are not allowed: Property '" +name + "' on bean class '" + bean.getClass() + "'");} else if (resolver.isIndexed(name)) {throw new IllegalArgumentException("Indexed property names are not allowed: Property '" +name + "' on bean class '" + bean.getClass() + "'");} else if (resolver.isMapped(name)) {throw new IllegalArgumentException("Mapped property names are not allowed: Property '" +name + "' on bean class '" + bean.getClass() + "'");}// Handle DynaBean instances speciallyif (bean instanceof DynaBean) {final DynaProperty descriptor =((DynaBean)bean).getDynaClass().getDynaProperty(name);if (descriptor == null) {throw new NoSuchMethodException("Unknown property '" +name + "' on dynaclass '" +((DynaBean)bean).getDynaClass() + "'");}((DynaBean)bean).set(name, value);return;}// Retrieve the property setter method for the specified propertyfinal PropertyDescriptor descriptor =getPropertyDescriptor(bean, name);if (descriptor == null) {throw new NoSuchMethodException("Unknown property '" +name + "' on class '" + bean.getClass() + "'");}// 通过 PropertyDescriptor 获取道理 set 方法 的 Methodfinal Method writeMethod = getWriteMethod(bean.getClass(), descriptor);if (writeMethod == null) {throw new NoSuchMethodException("Property '" + name +"' has no setter method in class '" + bean.getClass() + "'");}// Call the property setter methodfinal Object[] values = new Object[1];values[0] = value;if (log.isTraceEnabled()) {final String valueClassName =value == null ? "<null>" : value.getClass().getName();log.trace("setSimpleProperty: Invoking method " + writeMethod+ " with value " + value + " (class " + valueClassName + ")");}// 这个方法就是 简单的 writeMethod 调用 invoke 方法 这样子我们的值就设置好了invokeMethod(writeMethod, bean, values);

好了，这样子一个值就复制到新的对象里面了，是不是很简单？

总结

今天学习了 Apache BeanUtils 的源码，总体上就是一个缓存+反射的调用，看是记不住的，大家赶快打开自己的电脑跟几遍源码吧。

后面还会带大家看 Spring BeanUtils 的源码，欢迎持续关注。

写在最后

给大家推荐一个非常完整的Java项目搭建的最佳实践,也是本文的源码出处，由大厂程序员&EasyExcel作者维护，地址：https://github.com/zhuangjiaju/easytools