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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
简单的复制对象
直接上代码：
创建一个java 对象：
java
/**
* 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:
text
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：
java
/**
* 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
java
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
java
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 copyProperties
BeanUtilsBean.getInstance().copyProperties(dest, orig);
}org.apache.commons.beanutils.BeanUtilsBean.copyProperties
java
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 <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
java
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
java
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 context
log.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
java
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 bean
Object 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 require
final String propName = resolver.getProperty(name); // Simple name of target property
Class<?> type = null; // Java type of target property
final 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 type
if (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 only
if (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 it
if (index >= 0) { // Destination must be indexed
value = 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 simple
value = 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
java
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 name
if (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 specially
if (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 property
final 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 Method
final 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 method
final 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