混淆java.beans.PropertyDescriptor的行为（字符串，类）

Question

我想为我有的bean类创建一个PropertyDescriptor。我打电话

new PropertyDescriptor(myProperty, myClass) 

我看到一个异常，“isMyProperty”方法不存在。 偷看一下代码 -

/** 
* Constructs a PropertyDescriptor for a property that follows 
* the standard Java convention by having getFoo and setFoo 
* accessor methods. Thus if the argument name is "fred", it will 
* assume that the writer method is "setFred" and the reader method 
* is "getFred" (or "isFred" for a boolean property). Note that the 
* property name should start with a lower case character, which will 
* be capitalized in the method names. 
* 
* @param propertyName The programmatic name of the property. 
* @param beanClass The Class object for the target bean. For 
*  example sun.beans.OurButton.class. 
* @exception IntrospectionException if an exception occurs during 
*    introspection. 
*/ 
public PropertyDescriptor(String propertyName, Class<?> beanClass) 
    throws IntrospectionException { 
this(propertyName, beanClass, 
    "is" + capitalize(propertyName), 
    "set" + capitalize(propertyName)); 
} 

的文件说，它会寻找“getFred”，但它总是使用"is" + capitalize(property)！这是Java版本“1.6.0_31”

想法？

Answer 1

编辑：我想我知道你的问题是什么。如果该类不存在于你的类中，那么你会得到“isProperty”方法错误。见我的例子：

{ 
     PropertyDescriptor desc = new PropertyDescriptor("uuid", Company.class); 
     Method m = desc.getReadMethod(); 
     System.out.println(m.getName()); /* prints getUuid */ 
    } 
    { 
     PropertyDescriptor desc = new PropertyDescriptor("uuid11", Company.class); 
     Method m = desc.getReadMethod(); 
     System.out.println(m.getName()); /* throws Method not found: isUuid11 */ 
    } 

---

原文：

看起来它只是默认为isProperty作为读取方法，如果不存在的话，它使用的getProperty。看看在getReadMethod方法，该位，哪里就有奇迹：

if (readMethod == null) { 
    readMethodName = "get" + getBaseName(); 

所以它首先尝试isProperty方法，如果没有该方法，查找的getProperty。

下面是完整的方法：

public synchronized Method getReadMethod() { 
Method readMethod = getReadMethod0(); 
if (readMethod == null) { 
    Class cls = getClass0(); 
    if (cls == null || (readMethodName == null && readMethodRef == null)) { 
     // The read method was explicitly set to null. 
     return null; 
    } 
    if (readMethodName == null) { 
     Class type = getPropertyType0(); 
     if (type == boolean.class || type == null) { 
      readMethodName = "is" + getBaseName(); 
     } else { 
      readMethodName = "get" + getBaseName(); 
     } 
    } 

    // Since there can be multiple write methods but only one getter 
    // method, find the getter method first so that you know what the 
    // property type is. For booleans, there can be "is" and "get" 
    // methods. If an "is" method exists, this is the official 
    // reader method so look for this one first. 
    readMethod = Introspector.findMethod(cls, readMethodName, 0); 
    if (readMethod == null) { 
     readMethodName = "get" + getBaseName(); 
     readMethod = Introspector.findMethod(cls, readMethodName, 0); 
    } 
    try { 
     setReadMethod(readMethod); 
    } catch (IntrospectionException ex) { 
    // fall 
    } 
} 
return readMethod; 
} 

Answer 2

如果你的财产是原始布尔然后PropertyDescriptor的寻找“isProperty”的方法。 如果你的属性是装箱布尔值，然后PropertyDescriptor寻找“getProperty”方法。

Answer 3

我有类似的问题，我解决了这个问题。

static Object get(final String name, final Object obj) 
    throws ReflectiveOperationException { 

    final Class<?> klass = obj.getClass(); 

    try { 
     final BeanInfo info = Introspector.getBeanInfo(klass); 
     for (final PropertyDescriptor descriptor 
      : info.getPropertyDescriptors()) { 
      if (name.equals(descriptor.getName())) { 
       final Method reader = descriptor.getReadMethod(); 
       if (reader != null) { 
        if (!reader.isAccessible()) { 
         reader.setAccessible(true); 
        } 
        return reader.invoke(obj); 
       } 
       break; // anyway 
      } 
     } 
    } catch (final IntrospectionException ie) { 
     ie.printStackTrace(System.err); 
    } 

    final Field field = findField(obj.getClass(), name); 
    logger.log(Level.WARNING, "trying to get value directly from {0}", 
       new Object[]{field}); 
    if (!field.isAccessible()) { 
     field.setAccessible(true); 
    } 
    return field.get(obj); 
} 

Answer 4

我曾与一个名为“ip_value”场类似的问题。 我最初的getter和setter方法分别是getIPValue()和setIPValue()。 分别将它们重命名为getIp_value()和setIp_value()后，问题得到解决。