java PropertyDescriptor 应用及源码分析

java PropertyDescriptor 应用及源码分析

1. 概述

PropertyDescriptor描述Java Bean中通过一对存储器方法（getter / setter）导出的一个属性。我们可以通过该PropertyDescriptor对bean中的该属性进行读取和写入操作，也可以设置其getter / setter。

2. 关键接口及内部属性

public PropertyDescriptor(String name, Class<?> beanClass) throws IntrospectionException  
public PropertyDescriptor(String name, Class<?> beanClass, String getMethodName, String setMethodName) throws IntrospectionException public PropertyDescriptor(String name, Method readMethod, Method writeMethod) throws IntrospectionException public Class<?> getPropertyType() public Method getReadMethod() public Method getWriteMethod() public void setReadMethod(Method readMethod) throws IntrospectionException public void setWriteMethod(Method writeMethod) public boolean equals(Object o) 

相关的PropertyDescriptor内部属性如下： 
Class<?> propertyType; //该属性的类型 
Method getMethod; //getter 
Method setMethod; //setter 
还有继承自其父类FeatureDescriptor的功能，用于指定该属性的编程名称

3. 简单应用

现有Person类如下：

package com.cwind.property;  

public class Person { private String name ; private int age ; public Person(){ this.name = ""; this.age = 0; } public Person(String name, int age) { super(); this.name = name; this. age = age; } public String getName() { return name; } public void setName(String name) { this. name = name; } public int getAge() { return age; } public void setAge(int age) { this. age = age; } public String getNameInUpperCase(){ return this .name .toUpperCase(); } public void setNameToLowerCase(String name){ this.name = name.toLowerCase(); } } 

该类中除了name和age两个属性的标准getter和setter之外，还有增加了一个获取大写name的get方法和一个将name设置为小写的set方法。 
在测试类中，首先获得这两个方法对象。

Class personClass = Class.forName("com.cwind.property.Person");  
Method read = personClass.getMethod("getNameInUpperCase", null);  
Method write = personClass.getMethod("setNameToLowerCase", String.class );  //然后可以通过两种方式构造PropertyDescriptor PropertyDescriptor prop1 = new PropertyDescriptor( "name", Person.class );  //使用其标准getter和setter PropertyDescriptor prop2 = new PropertyDescriptor( "name", read, write);  //使用read和write两个方法对象所自定义的getter和setter  //下面构建一个Person对象 Person person = new Person("Kobe" , 36); System. out.println(prop1.getReadMethod().invoke(person, null));  // --实际调用Person.getName(), result: Kobe System. out.println(prop2.getReadMethod().invoke(person, null));  // --实际调用Person.getNameInUpperCase(), result: KOBE prop1.getWriteMethod().invoke(person, "James");  // --实际调用Person.setName(), person.name被设置为James prop2.getWriteMethod().invoke(person, "James");  // --实际调用Person.setNameToLowerCase(), person.name被设置为james 

4. 源码分析

构造函数1：

public PropertyDescriptor(String name, Class<?> beanClass)  
        throws IntrospectionException {  
        setName(name);     //设置属性编程名，本例中即'name'  
        if (name.length() == 0){ throw new IntrospectionException("empty property name"); // 编程名为空则抛出异常 } String caps = Character.toUpperCase(name.charAt(0)) + name.substring(1); // 标准getter应为getName()或isName(), 先将首字母大写 findMethods(beanClass, "is" + caps, "get" + caps, "set" + caps); // 参数依次为：类类型，可能的getter函数名1，可能的getter函数名2，setter函数名 if (getMethod == null){ // findMethods()设置PropertyDescriptor的getMethod和setMethod属性 throw new IntrospectionException( "Cannot find a is" + caps + " or get" + caps + " method"); } if (setMethod == null){ throw new IntrospectionException( "Cannot find a " + caps + " method" ); } propertyType = checkMethods(getMethod, setMethod); // checkMethods()函数用来检测getMethod得到的类型与setMethod的参数类型是否匹配，若匹配则置propertyType为该类型 } 

构造函数2： 
public PropertyDescriptor(String name, Class

private void findMethods(Class beanClass, String getMethodName1, String getMethodName2, String setMethodName) throws IntrospectionException { try { // 首先查找getMethodName1指定的getter (isXXX) if (getMethodName1 != null) { try { getMethod = beanClass.getMethod(getMethodName1, new Class[0]); } catch (NoSuchMethodException e) {} } // 若失败，则查找getMethodName2指定的getter (getXXX) if (getMethod == null && getMethodName2 != null) { try { getMethod = beanClass.getMethod(getMethodName2, new Class[0]); } catch (NoSuchMethodException e) {} } if (setMethodName != null) { if (getMethod != null) { // 如果得到了getMethod，则通过其返回值类型决定setMethod的参数类型 Class propertyType = getMethod.getReturnType(); if (propertyType == Void.TYPE) { // 若getter的返回值为Void类型则抛出异常 String msg = "The property's read method has return type 'void'"; throw new IntrospectionException(msg); } Class[] setArgs = new Class[] { propertyType }; try { setMethod = beanClass.getMethod(setMethodName, setArgs); // 通过函数名和参数类型获得setMethod } catch (NoSuchMethodException e) {} } else if (getMethodName1 == null && getMethodName2 == null) { // getMethodName1和2均为空，则此属性为只写属性，此时遍历bean中的函数，返回第一个名称与setMethodName一致且返回类型为Void的单参数函数 Method[] methods = beanClass.getMethods(); for (int i = 0; i < methods.length; i++) { if (methods[i].getName().equals(setMethodName) && methods[i].getParameterTypes().length == 1 && methods[i].getReturnType() == Void.TYPE) { setMethod = methods[i]; break; } } } } } catch (SecurityException e) { String msg = "SecurityException thrown on attempt to access methods."; // 作者在纠结要不要修改异常类型 throw new IntrospectionException(msg); } } 

checkMethods方法

private Class<?> checkMethods(Method readMethod, Method writeMethod) throws IntrospectionException {  
        Class<?> newPropertyType = propertyType;  
         // 合法的read方法应该无参同时带有一个非空的返回值类型  
        if (readMethod != null) { if (readMethod.getParameterTypes().length > 0) { throw new IntrospectionException("read method has unexpected parameters"); } newPropertyType = readMethod.getReturnType(); if (newPropertyType == Void.TYPE) { throw new IntrospectionException("read method return type is void"); } } // 合法的write方法应该包含一个类型相同的参数 if (writeMethod != null) { if (writeMethod.getParameterTypes().length != 1) { // 参数不能超过一个 String msg = "write method does not have exactly one parameter" ; throw new IntrospectionException(msg); } if (readMethod == null) { // 若无read方法，属性类型就应为writeMethod的参数类型 newPropertyType = writeMethod.getParameterTypes()[0]; } else { // 检查read方法的返回值类型是否与write方法的参数类型相匹配 if (newPropertyType != null && !newPropertyType.isAssignableFrom( writeMethod.getParameterTypes()[0])) { throw new IntrospectionException("read and write method are not compatible"); } } } return newPropertyType; } 

最后提一句PropertyDescriptor.equals(), 只有当属性类型、标志、读写方法和PropertyEditorClass均相同时才认为两个PropertyDescriptor相等

return samePropertyType  
                && sameFlags  
                && sameReadMethod  
                && sameWriteMethod  
                && samePropertyEditorClass;  

转载自：http://cwind.iteye.com/blog/2028208?utm_source=tuicool 

参考：http://blog.csdn.net/z69183787/article/details/8443777

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