Apache BeanUtils 拷贝属性的实现

先说坑:

  1. 对于装箱的Boolean类型,不能用isABCsetABC的组合,只能用getABCsetABC的组合(对于任何非基本类型,都是这样)
  2. beanUtils的BeanUtils.copyProperties看的不是成员,而是getset方法,也就是属性(property),对于基本boolean是看isset

 

本文环境:

java version "1.8.0"
Java(TM) SE Runtime Environment (build 1.8.0-b132)
Java HotSpot(TM) 64-Bit Server VM (build 25.0-b70, mixed mode) 

commons-beanutils 1.9.2

实现:

通过class获取BeanInfobeanInfo = Introspector.getBeanInfo(icontext.getTargetClass()); 

具体代码在 org.apache.commons.beanutils.DefaultBeanIntrospector.introspect(IntrospectionContext icontext) line 88 

BeanInfo中描述了很多属性如:

对于方法的描述在methods中,对于属性(Property)的描述在PropertiesDescripter中。

最终copy的时候是通过反射调用readMethodNamewriteMethodName来进行的复制,在复制之前还会进行类型的检查。

 

注意:

对于属性的获取是通过javaIntrospector来获取的并不是直接反射的私有成员变量。Introspector这个类Eclipsedebug的时候无法追踪临时变量,原因未知

如果对于装箱的Boolean类型使用isset,会出现如下情况:

 

readMethodName是一个null…

 

看下Introspector类往下走,获取类的Properties的源码如下(在Introspector.getTargetPropertyInfo方法里,line : 507):

try {

    if (argCount == 0) {

        if (name.startsWith(GET_PREFIX)) {

            // Simple getter

            pd = new PropertyDescriptor(this.beanClass, name.substring(3), method, null);

        } else if (resultType == boolean.class && name.startsWith(IS_PREFIX)) {

            //上面的这个是小写的boolean.class 并不是Boolean.class,指的是基本类型的那个boolean

            // Boolean getter

            pd = new PropertyDescriptor(this.beanClass, name.substring(2), method, null);

        }

    } else if (argCount == 1) {

        if (int.class.equals(argTypes[0]) && name.startsWith(GET_PREFIX)) {

            pd = new IndexedPropertyDescriptor(this.beanClass, name.substring(3), null, null, method, null);

        } else if (void.class.equals(resultType) && name.startsWith(SET_PREFIX)) {

            // Simple setter

            pd = new PropertyDescriptor(this.beanClass, name.substring(3), null, method);

            if (throwsException(method, PropertyVetoException.class)) {

                pd.setConstrained(true);

            }

        }

    } else if (argCount == 2) {

        if (void.class.equals(resultType) && int.class.equals(argTypes[0]) && name.startsWith(SET_PREFIX)) {

            pd = new IndexedPropertyDescriptor(this.beanClass, name.substring(3), null, null, null, method);

            if (throwsException(method, PropertyVetoException.class)) {

                pd.setConstrained(true);

            }

        }

    }

} catch (IntrospectionException ex) {

    // This happens if a PropertyDescriptor or IndexedPropertyDescriptor

    // constructor fins that the method violates details of the deisgn

    // pattern, e.g. by having an empty name, or a getter returning

    // void , or whatever.

    pd = null;

}

}

  

原理还是根据setget/isset去割字符串然后拼接property

java对于java bean的规范可以在这里下载:

 

其中关于Property有如下说明:

 

7 Properties

Properties are discrete, named attributes of a Java Bean that can affect its appearance or its behaviour.

Properties show up in a number of ways:

1. Properties may be exposed in scripting environments as though they were fields of

objects. So in a Javascript environment I might do “b.Label = foo” to set the value of a

property.

2. Properties can be accessed programmatically by other components calling their getter

and setter methods (see Section 7.1 below).

3. As part of the process of customizing a component (see Section 9), its properties may

be presented in a property sheet for a user to edit.

4. Typically a bean’s properties will be persistent, so that their state will be stored away

as part of the persistent state of the bean.

Properties can have arbitrary types, including both built-in Java types such as “int” and class

or interfaces types such as “java.awt.Color”.

 

7.1 Accessor methods

Properties are always accessed via method calls on their owning object. For readable properties

there will be a getter method to read the property value. For writable properties there will be a

setter method to allow the property value to be updated. Thus even when a script writer types

in something such as “b.Label = foo” there is still a method call into the target object to set the

property, and the target object has full programmatic control.

So properties need not just be simple data fields, they can actually be computed values. Updates

may have various programmatic side effects. For example, changing a bean’s background color

property might also cause the bean to be repainted with the new color.

For simple properties the accessor type signatures are:

void setFoo(PropertyType value); // simple setter

PropertyType getFoo(); // simple getter

GetFoo and setFoo are simply example names. Accessor methods can have arbitrary names.

However for standard naming conventions for accessor methods see the design patterns described

in Section 8.3.

 

 

8.3 Design Patterns for Properties

8.3.1 Simple properties

By default, we use design patterns to locate properties by looking for methods of the form:

public <PropertyType> get<PropertyName>();

public void set<PropertyName>(<PropertyType> a);

If we discover a matching pair of “get<PropertyName>” and “set<PropertyName>” methods

that take and return the same type, then we regard these methods as defining a read-write property

whose name will be “<propertyName>”. We will use the “get<PropertyName>” method

to get the property value and the “set<PropertyName>” method to set the property value. The

pair of methods may be located either in the same class or one may be in a base class and the

other may be in a derived class.

If we find only one of these methods, then we regard it as defining either a read-only or a writeonly

property called “<propertyName>”

By default we assume that properties are neither bound nor constrained (see Section 7).

So a simple read-write property “foo” might be represented by a pair of methods:

public Wombat getFoo();

public void setFoo(Wombat w);

8.3.2 Boolean properties

In addition, for boolean properties, we allow a getter method to match the pattern:

public boolean is<PropertyName>();

This “is<PropertyName>” method may be provided instead of a “get<PropertyName>” method,

or it may be provided in addition to a “get<PropertyName>” method.

In either case, if the “is<PropertyName>” method is present for a boolean property then we will

use the “is<PropertyName>” method to read the property value.

An example boolean property might be:

public boolean isMarsupial();

public void setMarsupial(boolean m);

 

posted @ 2015-07-20 22:50  ctgulong  阅读(2954)  评论(0编辑  收藏  举报