Spring FrameWork－beans包－属性编辑器(PropertyEditor)

lendo — Wed, 04 Apr 2007 04:55:00 GMT

        本来想把beans包放到一篇文章中来记录得，不过随着学习得深入，发现原来就是这一个包，也有很多得机制需要详细得描述，所以我还是把原来的文档拆分成几个部分，这样我以后review自己学习的时候也比较清楚。
     首先应该说明一下什么是属性编辑器，在Spring的应用中经常要遇到这种情况，JavaBean的值是在运行的时候动态地从配置文件中注入的，而配置文件中属性的值都是String类型的，对应的JavaBean中却有其他很多类型，如Date,Integer,Byte等，所以属性编辑器的任务就是在Spring进行注入这个动作的时候，将String类型的数据转化为JavaBean对应的类型。
     比如如下这段代码，UserBean是一个标准的JavaBean，有Integer id和String userName两个属性。

     public class TestBeanWrapper extends TestCase {
         public void testPropertyEditor() throws Exception{
             Object obj = Class.forName("com.ws.po.UserBean").newInstance();
             BeanWrapper bw = new BeanWrapperImpl(obj);（A）//这里就要做注册属性编辑器的工作
             bw.setPropertyValue("id", "1");（B）
             System.out.println(bw.getPropertyValue("id").getClass());（C）
         }
     }

     在代码A这里，就需要注册属性编辑器，也是Spring Ioc机制的关键部分。
     在代码B这里，我并没有传入new Integer(1)，而是直接传入了一个字符串“1”。
     在代码C这里，就得到了我想要的类型，输出结果为：class java.lang.Integer。
     如果你试图在B代码这里，将“1”更换为“SSSS”字符串，那么会得到一个TypeMismatchException，提示无法转换。

     那么在代码A这里到底发生了些什么呢(只针对属性编辑器来讲)？下面一层层地往里面走。
    这段代码里面没有任何的有关属性编辑器的代码，那么就只有往BeanWrapperImpl里面查找。

     public BeanWrapperImpl(Object object) {
         registerDefaultEditors();//这里就开始注册默认的属性编辑器了
         setWrappedInstance(object);
     }

      BeanWrapperImpl类继承自AbstractPropertyAccessor抽象类，AbstractPropertyAccessor类又继承自PropertyEditorRegistrySupport类，在PropertyEditorRegistrySupport中就实现了registerDefaultEditors()这个方法，代码如下：

     protected void registerDefaultEditors() {
         this.defaultEditors = new HashMap(32);

         // Simple editors, without parameterization capabilities.
         // The JDK does not contain a default editor for any of these target types.
         this.defaultEditors.put(Class.class, new ClassEditor());
         this.defaultEditors.put(Class[].class, new ClassArrayEditor());
         this.defaultEditors.put(File.class, new FileEditor());
         this.defaultEditors.put(InputStream.class, new InputStreamEditor());
         this.defaultEditors.put(Locale.class, new LocaleEditor());
         this.defaultEditors.put(Properties.class, new PropertiesEditor());
         this.defaultEditors.put(Resource[].class, new ResourceArrayPropertyEditor());
         this.defaultEditors.put(URL.class, new URLEditor());

         // Register JDK-1.4-specific editors.
         if (JdkVersion.isAtLeastJava14()) {
             this.defaultEditors.put(URI.class, new URIEditor());
             this.defaultEditors.put(Pattern.class, new PatternEditor());
         }

         // Default instances of collection editors.
         // Can be overridden by registering custom instances of those as custom editors.
         this.defaultEditors.put(Collection.class, new CustomCollectionEditor(Collection.class));
         this.defaultEditors.put(Set.class, new CustomCollectionEditor(Set.class));
         this.defaultEditors.put(SortedSet.class, new CustomCollectionEditor(SortedSet.class));
         this.defaultEditors.put(List.class, new CustomCollectionEditor(List.class));
         this.defaultEditors.put(SortedMap.class, new CustomMapEditor(SortedMap.class));

         // Default editors for primitive arrays.
         this.defaultEditors.put(byte[].class, new ByteArrayPropertyEditor());
         this.defaultEditors.put(char[].class, new CharArrayPropertyEditor());

         // The JDK does not contain a default editor for char!
         this.defaultEditors.put(char.class, new CharacterEditor(false));
         this.defaultEditors.put(Character.class, new CharacterEditor(true));

         // Spring's CustomBooleanEditor accepts more flag values than the JDK's default editor.
         this.defaultEditors.put(boolean.class, new CustomBooleanEditor(false));
         this.defaultEditors.put(Boolean.class, new CustomBooleanEditor(true));

         // The JDK does not contain default editors for number wrapper types!
         // Override JDK primitive number editors with our own CustomNumberEditor.
         this.defaultEditors.put(byte.class, new CustomNumberEditor(Byte.class, false));
         this.defaultEditors.put(Byte.class, new CustomNumberEditor(Byte.class, true));
         this.defaultEditors.put(short.class, new CustomNumberEditor(Short.class, false));
         this.defaultEditors.put(Short.class, new CustomNumberEditor(Short.class, true));
         this.defaultEditors.put(int.class, new CustomNumberEditor(Integer.class, false));
         this.defaultEditors.put(Integer.class, new CustomNumberEditor(Integer.class, true));
        this.defaultEditors.put(long.class, new CustomNumberEditor(Long.class, false));
         this.defaultEditors.put(Long.class, new CustomNumberEditor(Long.class, true));
         this.defaultEditors.put(float.class, new CustomNumberEditor(Float.class, false));
         this.defaultEditors.put(Float.class, new CustomNumberEditor(Float.class, true));
         this.defaultEditors.put(double.class, new CustomNumberEditor(Double.class, false));
         this.defaultEditors.put(Double.class, new CustomNumberEditor(Double.class, true));
         this.defaultEditors.put(BigDecimal.class, new CustomNumberEditor(BigDecimal.class, true));
         this.defaultEditors.put(BigInteger.class, new CustomNumberEditor(BigInteger.class, true));
    }

lendo 2007-04-04 12:55 发表评论

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Spring FrameWork－beans包－属性编辑器(PropertyEditor)