java冷知识：java bean内省模式与spring bean的关联

短命女 2022-04-03 08:07 292阅读 0赞

最近一直整理着[搜索引擎][Link 1]相关的主题，后续也准备多分享一些spring相关的技术。正所谓温故而知新，java bean内省模式对spring bean的影响非常深，真可谓是青出于蓝而胜于蓝。

**目录**

1. JavaBean Introspector

1.1 BeanDescriptor

1.2 MethodDescriptor

1.3 PropertyDescriptor

1.4 ParameterDescriptor

1.5 Introspector

1.6 属性变化监听

2. spring bean

2.1 PropertyEditorRegistry

2.2 PropertyEditorRegistrar

2.3 CustomEditorConfigurer

2.4 PropertyAccessor和BeanWrapper

--------------------

## 1. JavaBean Introspector ##

Java的内省机制其实是基于JavaBean的，那么，什么是JavaBean哪？我们可以这样说，我们在项目中经常用到的Model可以充当JavaBean，其实我对于JavaBean的理解是它要满足以下几个特征：

*  有属性可以保存的成员变量
 *  有空参构造方法
 *  属性由对应get/set方法。

而内省(Introspector) 是Java语言对JavaBean**类属性**、**事件**的一种缺省处理方法。类User中有属性userName，那我们可以通过getUserName,setUserName来得到其值或者设置新的值。通过getUserName/setUserName来访问userName属性，这就是**默认的规则**。Sun JDK中提供了**一套API**用来访问某个属性的getter/setter方法，这就是内省。

### 1.1 BeanDescriptor ###

BeanDescriptor就是**bean描述符**，源码

package java.beans;
    
    public class BeanDescriptor extends FeatureDescriptor {
        private Reference<? extends Class<?>> beanClassRef;
        private Reference<? extends Class<?>> customizerClassRef;
    
        public BeanDescriptor(Class<?> var1) {
            this(var1, (Class)null);
        }
    
        public BeanDescriptor(Class<?> var1, Class<?> var2) {
            this.beanClassRef = getWeakReference(var1);
            this.customizerClassRef = getWeakReference(var2);
    
            String var3;
            for(var3 = var1.getName(); var3.indexOf(46) >= 0; var3 = var3.substring(var3.indexOf(46) + 1)) {
                ;
            }
    
            this.setName(var3);
        }
    
        public Class<?> getBeanClass() {
            return this.beanClassRef != null?(Class)this.beanClassRef.get():null;
        }
    
        public Class<?> getCustomizerClass() {
            return this.customizerClassRef != null?(Class)this.customizerClassRef.get():null;
        }
    
        BeanDescriptor(BeanDescriptor var1) {
            super(var1);
            this.beanClassRef = var1.beanClassRef;
            this.customizerClassRef = var1.customizerClassRef;
        }
    
        void appendTo(StringBuilder var1) {
            appendTo(var1, "beanClass", this.beanClassRef);
            appendTo(var1, "customizerClass", this.customizerClassRef);
        }
    }

### 1.2 MethodDescriptor ###

MethodDescriptor就是**方法描述符**，

package java.beans;
    public class MethodDescriptor extends FeatureDescriptor {
    
        private final MethodRef methodRef = new MethodRef();
    
        private String[] paramNames;
    
        private List<WeakReference<Class<?>>> params;
    
        private ParameterDescriptor parameterDescriptors[];
    
        /**
         * Constructs a <code>MethodDescriptor</code> from a
         * <code>Method</code>.
         *
         * @param method    The low-level method information.
         */
        public MethodDescriptor(Method method) {
            this(method, null);
        }
    
    
        /**
         * Constructs a <code>MethodDescriptor</code> from a
         * <code>Method</code> providing descriptive information for each
         * of the method's parameters.
         *
         * @param method    The low-level method information.
         * @param parameterDescriptors  Descriptive information for each of the
         *                          method's parameters.
         */
        public MethodDescriptor(Method method,
                    ParameterDescriptor parameterDescriptors[]) {
            setName(method.getName());
            setMethod(method);
            this.parameterDescriptors = (parameterDescriptors != null)
                    ? parameterDescriptors.clone()
                    : null;
        }
    }

### 1.3 PropertyDescriptor ###

PropertyDescriptor就是**字段描述符**，

package java.beans;
    public class PropertyDescriptor extends FeatureDescriptor {
    
        private Reference<? extends Class<?>> propertyTypeRef;
        private final MethodRef readMethodRef = new MethodRef();
        private final MethodRef writeMethodRef = new MethodRef();
        private Reference<? extends Class<?>> propertyEditorClassRef;
    
        private boolean bound;
        private boolean constrained;
    
        // The base name of the method name which will be prefixed with the
        // read and write method. If name == "foo" then the baseName is "Foo"
        private String baseName;
    
        private String writeMethodName;
        private String readMethodName;
    
        /**
         * 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,
                    Introspector.IS_PREFIX + NameGenerator.capitalize(propertyName),
                    Introspector.SET_PREFIX + NameGenerator.capitalize(propertyName));
        }
    }

### 1.4 ParameterDescriptor ###

ParameterDescriptor就是**参数描述符**

package java.beans;
    public class ParameterDescriptor extends FeatureDescriptor {
        /**
         * Public default constructor.
         */
        public ParameterDescriptor() {
        }
    
        /**
         * Package private dup constructor.
         * This must isolate the new object from any changes to the old object.
         */
        ParameterDescriptor(ParameterDescriptor old) {
            super(old);
        }
    }

### 1.5 Introspector ###

Introspector将JavaBean中的属性封装起来进行操作（**读取**）。在程序把一个类当做JavaBean来看，就是调用Introspector.getBeanInfo()方法，得到**BeanInfo**对象。那修改怎么办？当然是只能反射了（java.lang.reflect）

<table> 
 <tbody> 
  <tr> 
   <td style="width:265px;">构造器</td> 
   <td style="width:584px;">java.lang.reflect.Constructor&lt;T&gt;</td> 
  </tr> 
  <tr> 
   <td style="width:265px;">方法</td> 
   <td style="width:584px;">java.lang.reflect.Method</td> 
  </tr> 
  <tr> 
   <td style="width:265px;">字段</td> 
   <td style="width:584px;">java.lang.reflect.Field</td> 
  </tr> 
 </tbody> 
</table>

@Test
    public void go_getDescriptor() throws IntrospectionException {
        BeanInfo beanInfo = Introspector.getBeanInfo(User.class);
        System.out.println(beanInfo.getBeanDescriptor());
        System.out.println(Arrays.toString(beanInfo.getMethodDescriptors()));
        System.out.println(Arrays.toString(beanInfo.getPropertyDescriptors()));
    }
    
    @Test
    public void go_setAge() throws IntrospectionException, InvocationTargetException, IllegalAccessException {
        User userInfo = new User();
        String age = "age";
        Object ageValue = 19;
        BeanInfo beanInfo = Introspector.getBeanInfo(User.class);
        PropertyDescriptor[] proDescrtptors = beanInfo.getPropertyDescriptors();
        if (proDescrtptors != null && proDescrtptors.length > 0) {
            for (PropertyDescriptor propDesc : proDescrtptors) {
                if (propDesc.getName().equals(age)) {
                    Method methodSetUserName = propDesc.getWriteMethod();//很重要的原则
                    methodSetUserName.invoke(userInfo,ageValue);
                    Method methodGetUserName = propDesc.getReadMethod();
                    System.out.println(methodGetUserName.invoke(userInfo)); //output:19
                    break;
                }
            }
        }
    }

> go\_getDescriptor的输出：
> 
> java.beans.BeanDescriptor\[name=BeanInfo\_test$User; beanClass=class com.example.introspector.BeanInfo\_test$User\]
> 
> \[java.beans.MethodDescriptor\[name=getClass; method=public final native java.lang.Class java.lang.Object.getClass()\], java.beans.MethodDescriptor\[name=getUserName; method=public java.lang.String com.example.introspector.BeanInfo\_test$User.getUserName()\], java.beans.MethodDescriptor\[name=setAge; method=public void com.example.introspector.BeanInfo\_test$User.setAge(int)\], java.beans.MethodDescriptor\[name=getAge; method=public int com.example.introspector.BeanInfo\_test$User.getAge()\], java.beans.MethodDescriptor\[name=wait; method=public final void java.lang.Object.wait() throws java.lang.InterruptedException\], java.beans.MethodDescriptor\[name=notifyAll; method=public final native void java.lang.Object.notifyAll()\], java.beans.MethodDescriptor\[name=notify; method=public final native void java.lang.Object.notify()\], java.beans.MethodDescriptor\[name=wait; method=public final void java.lang.Object.wait(long,int) throws java.lang.InterruptedException\], java.beans.MethodDescriptor\[name=setUserName; method=public void com.example.introspector.BeanInfo\_test$User.setUserName(java.lang.String)\], java.beans.MethodDescriptor\[name=hashCode; method=public native int java.lang.Object.hashCode()\], java.beans.MethodDescriptor\[name=wait; method=public final native void java.lang.Object.wait(long) throws java.lang.InterruptedException\], java.beans.MethodDescriptor\[name=equals; method=public boolean java.lang.Object.equals(java.lang.Object)\], java.beans.MethodDescriptor\[name=toString; method=public java.lang.String java.lang.Object.toString()\]\]
> 
> \[java.beans.PropertyDescriptor\[name=age; propertyType=int; readMethod=public int com.example.introspector.BeanInfo\_test$User.getAge(); writeMethod=public void com.example.introspector.BeanInfo\_test$User.setAge(int)\], java.beans.PropertyDescriptor\[name=class; propertyType=class java.lang.Class; readMethod=public final native java.lang.Class java.lang.Object.getClass()\], java.beans.PropertyDescriptor\[name=userName; propertyType=class java.lang.String; readMethod=public java.lang.String com.example.introspector.BeanInfo\_test$User.getUserName(); writeMethod=public void com.example.introspector.BeanInfo\_test$User.setUserName(java.lang.String)\]\]

这里思考个问题：如果ageValue="19"，它就是非int，会报错（java.lang.IllegalArgumentException: argument type mismatch）该怎么办？其实是有解决方案的，继续往下看

### 1.6 属性变化监听 ###

一般事件触发流程都是这样的：传递一个字符串（Text，它叫法更专业，所以类型的原生形态文本型）类型**---》》》**把这个Text类型转换为对应的Java数据类型并赋值**---》》》**事件发生（不同的属性对应不同的事件）

**PropertyChangeEvent**，事件

package java.beans;
    public class PropertyChangeEvent extends EventObject {
        private static final long serialVersionUID = 7042693688939648123L;
        /**
         * Constructs a new {@code PropertyChangeEvent}.
         *
         * @param source        the bean that fired the event
         * @param propertyName  the programmatic name of the property that was changed
         * @param oldValue      the old value of the property
         * @param newValue      the new value of the property
         *
         * @throws IllegalArgumentException if {@code source} is {@code null}
         */
        public PropertyChangeEvent(Object source, String propertyName,
                                   Object oldValue, Object newValue) {
            super(source);
            this.propertyName = propertyName;
            this.newValue = newValue;
            this.oldValue = oldValue;
        }
    }

**PropertyChangeListener**，监听器

package java.beans;
    public interface PropertyChangeListener extends java.util.EventListener {
        /**
         * This method gets called when a bound property is changed.
         * @param evt A PropertyChangeEvent object describing the event source
         *          and the property that has changed.
         */
    
        void propertyChange(PropertyChangeEvent evt);
    }

**PropertyEditor**，事件源

package java.beans;
    public interface PropertyEditor {
       void setAsText(String text) throws java.lang.IllegalArgumentException;
       Object getValue();
    }
    public class PropertyEditorSupport implements PropertyEditor {
       public void setAsText(String text) throws java.lang.IllegalArgumentException {
            if (value instanceof String) {
                setValue(text);
                return;
            }
            throw new java.lang.IllegalArgumentException(text);
        }
        public void setValue(Object value) {
            this.value = value;
            firePropertyChange();
        }
        public void firePropertyChange() {
            java.util.Vector<PropertyChangeListener> targets;
            synchronized (this) {
                if (listeners == null) {
                    return;
                }
                targets = unsafeClone(listeners);
            }
            // Tell our listeners that "everything" has changed.
            PropertyChangeEvent evt = new PropertyChangeEvent(source, null, null, null);
    
            for (int i = 0; i < targets.size(); i++) {
                PropertyChangeListener target = targets.elementAt(i);
                target.propertyChange(evt);
            }
        }
    }

实例代码

Test
    public void go_setAgeToListener() throws IntrospectionException {
        User userInfo = new User();
        String age = "age";
        String ageValue = "19";
        BeanInfo beanInfo = Introspector.getBeanInfo(User.class);
        PropertyDescriptor[] proDescrtptors = beanInfo.getPropertyDescriptors();
        for (PropertyDescriptor propDesc : proDescrtptors) {
            if (propDesc.getName().equals(age)) {
                propDesc.setPropertyEditorClass(IntegerEditor.class);//很重要，也可以自定义
                PropertyEditor propertyEditor = propDesc.createPropertyEditor(null);
                propertyEditor.addPropertyChangeListener(x -> {
                    PropertyEditor source = (PropertyEditor) x.getSource();
                    Method methodSetUserName = propDesc.getWriteMethod();
                    try {
                        System.out.println("newValue:" + source.getValue());
                        methodSetUserName.invoke(userInfo, source.getValue());
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                });
                propertyEditor.setAsText(ageValue);
                break;
            }
        }
    }

## 2. spring bean ##

### ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2l0c29mdGNoZW5mZWk_size_16_color_FFFFFF_t_70][]   2.1 PropertyEditorRegistry ###

属性编辑器的注册表，实现类就老厉害了

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2l0c29mdGNoZW5mZWk_size_16_color_FFFFFF_t_70 1][]

public class PropertyEditorRegistrySupport implements PropertyEditorRegistry {
        private static Class<?> pathClass;
        private static Class<?> zoneIdClass;
        private ConversionService conversionService;
        private boolean defaultEditorsActive = false;
        private boolean configValueEditorsActive = false;
        private Map<Class<?>, PropertyEditor> defaultEditors;
        private Map<Class<?>, PropertyEditor> overriddenDefaultEditors;
        private Map<Class<?>, PropertyEditor> customEditors;
        private Map<String, PropertyEditorRegistrySupport.CustomEditorHolder> customEditorsForPath;
        private Map<Class<?>, PropertyEditor> customEditorCache;
    
        public PropertyEditorRegistrySupport() {
        }
    
        public void setConversionService(ConversionService conversionService) {
            this.conversionService = conversionService;
        }
    
        public ConversionService getConversionService() {
            return this.conversionService;
        }
    
        protected void registerDefaultEditors() {
            this.defaultEditorsActive = true;
        }
    
        public void useConfigValueEditors() {
            this.configValueEditorsActive = true;
        }
    
        public void overrideDefaultEditor(Class<?> requiredType, PropertyEditor propertyEditor) {
            if(this.overriddenDefaultEditors == null) {
                this.overriddenDefaultEditors = new HashMap();
            }
    
            this.overriddenDefaultEditors.put(requiredType, propertyEditor);
        }
    
        public PropertyEditor getDefaultEditor(Class<?> requiredType) {
            if(!this.defaultEditorsActive) {
                return null;
            } else {
                if(this.overriddenDefaultEditors != null) {
                    PropertyEditor editor = (PropertyEditor)this.overriddenDefaultEditors.get(requiredType);
                    if(editor != null) {
                        return editor;
                    }
                }
    
                if(this.defaultEditors == null) {
                    this.createDefaultEditors();
                }
    
                return (PropertyEditor)this.defaultEditors.get(requiredType);
            }
        }
        //这里处理xml中常规的转换
        private void createDefaultEditors() {
            this.defaultEditors = new HashMap(64);
            this.defaultEditors.put(Charset.class, new CharsetEditor());
            this.defaultEditors.put(Class.class, new ClassEditor());
            this.defaultEditors.put(Class[].class, new ClassArrayEditor());
            this.defaultEditors.put(Currency.class, new CurrencyEditor());
            this.defaultEditors.put(File.class, new FileEditor());
            this.defaultEditors.put(InputStream.class, new InputStreamEditor());
            this.defaultEditors.put(InputSource.class, new InputSourceEditor());
            this.defaultEditors.put(Locale.class, new LocaleEditor());
            if(pathClass != null) {
                this.defaultEditors.put(pathClass, new PathEditor());
            }
    
            this.defaultEditors.put(Pattern.class, new PatternEditor());
            this.defaultEditors.put(Properties.class, new PropertiesEditor());
            this.defaultEditors.put(Reader.class, new ReaderEditor());
            this.defaultEditors.put(Resource[].class, new ResourceArrayPropertyEditor());
            this.defaultEditors.put(TimeZone.class, new TimeZoneEditor());
            this.defaultEditors.put(URI.class, new URIEditor());
            this.defaultEditors.put(URL.class, new URLEditor());
            this.defaultEditors.put(UUID.class, new UUIDEditor());
            if(zoneIdClass != null) {
                this.defaultEditors.put(zoneIdClass, new ZoneIdEditor());
            }
    
            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));
            this.defaultEditors.put(byte[].class, new ByteArrayPropertyEditor());
            this.defaultEditors.put(char[].class, new CharArrayPropertyEditor());
            this.defaultEditors.put(Character.TYPE, new CharacterEditor(false));
            this.defaultEditors.put(Character.class, new CharacterEditor(true));
            this.defaultEditors.put(Boolean.TYPE, new CustomBooleanEditor(false));
            this.defaultEditors.put(Boolean.class, new CustomBooleanEditor(true));
            this.defaultEditors.put(Byte.TYPE, new CustomNumberEditor(Byte.class, false));
            this.defaultEditors.put(Byte.class, new CustomNumberEditor(Byte.class, true));
            this.defaultEditors.put(Short.TYPE, new CustomNumberEditor(Short.class, false));
            this.defaultEditors.put(Short.class, new CustomNumberEditor(Short.class, true));
            this.defaultEditors.put(Integer.TYPE, new CustomNumberEditor(Integer.class, false));
            this.defaultEditors.put(Integer.class, new CustomNumberEditor(Integer.class, true));
            this.defaultEditors.put(Long.TYPE, new CustomNumberEditor(Long.class, false));
            this.defaultEditors.put(Long.class, new CustomNumberEditor(Long.class, true));
            this.defaultEditors.put(Float.TYPE, new CustomNumberEditor(Float.class, false));
            this.defaultEditors.put(Float.class, new CustomNumberEditor(Float.class, true));
            this.defaultEditors.put(Double.TYPE, 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));
            if(this.configValueEditorsActive) {
                StringArrayPropertyEditor sae = new StringArrayPropertyEditor();
                this.defaultEditors.put(String[].class, sae);
                this.defaultEditors.put(short[].class, sae);
                this.defaultEditors.put(int[].class, sae);
                this.defaultEditors.put(long[].class, sae);
            }
        }
    }

### 2.2 PropertyEditorRegistrar ###

它是PropertyEditorRegistry中的defaultEditors的功能拓展

//它本身是null实现，实现类BeanWrapperFieldSetMapper是真正的实现（向PropertyEditorRegistry中添加DataBinder到customEditors，DataBinder就老厉害了（想想springmvc的@RequestBody就懂了））
    public class DefaultPropertyEditorRegistrar implements PropertyEditorRegistrar {
    	private Map<Class<?>, PropertyEditor> customEditors;
    	/**
    	 * Register the custom editors with the given registry.
    	 * 
    	 * @see org.springframework.beans.PropertyEditorRegistrar#registerCustomEditors(org.springframework.beans.PropertyEditorRegistry)
    	 */
    	@Override
    	public void registerCustomEditors(PropertyEditorRegistry registry) {
    		if (this.customEditors != null) {
    			for (Entry<Class<?>, PropertyEditor> entry : customEditors.entrySet()) {
    				registry.registerCustomEditor(entry.getKey(), entry.getValue());
    			}
    		}
    	}
    	/**
    	 * Specify the {@link PropertyEditor custom editors} to register.
    	 * 
    	 * 
    	 * @param customEditors a map of Class to PropertyEditor (or class name to
    	 * PropertyEditor).
    	 * @see CustomEditorConfigurer#setCustomEditors(Map)
    	 */
    	public void setCustomEditors(Map<? extends Object, ? extends PropertyEditor> customEditors) {
    		this.customEditors = new HashMap<Class<?>, PropertyEditor>();
    		for (Entry<? extends Object, ? extends PropertyEditor> entry : customEditors.entrySet()) {
    			Object key = entry.getKey();
    			Class<?> requiredType = null;
    			if (key instanceof Class<?>) {
    				requiredType = (Class<?>) key;
    			}
    			else if (key instanceof String) {
    				String className = (String) key;
    				requiredType = ClassUtils.resolveClassName(className, getClass().getClassLoader());
    			}
    			else {
    				throw new IllegalArgumentException("Invalid key [" + key
    						+ "] for custom editor: needs to be Class or String.");
    			}
    			PropertyEditor value = entry.getValue();
    			this.customEditors.put(requiredType, value);
    		}
    	}
    
    }
    //处理xml中Resource、URL、File...、向PropertyEditorRegistry中添加registry.registerCustomEditor或overrideDefaultEditor(requiredType, editor)
    public class ResourceEditorRegistrar implements PropertyEditorRegistrar {
    
    	private static Class<?> pathClass;
    
    	static {
    		try {
    			pathClass = ClassUtils.forName("java.nio.file.Path", ResourceEditorRegistrar.class.getClassLoader());
    		}
    		catch (ClassNotFoundException ex) {
    			// Java 7 Path class not available
    			pathClass = null;
    		}
    	}
    	private final PropertyResolver propertyResolver;
    	private final ResourceLoader resourceLoader;
    	/**
    	 * Create a new ResourceEditorRegistrar for the given {@link ResourceLoader}
    	 * and {@link PropertyResolver}.
    	 * @param resourceLoader the ResourceLoader (or ResourcePatternResolver)
    	 * to create editors for (usually an ApplicationContext)
    	 * @param propertyResolver the PropertyResolver (usually an Environment)
    	 * @see org.springframework.core.env.Environment
    	 * @see org.springframework.core.io.support.ResourcePatternResolver
    	 * @see org.springframework.context.ApplicationContext
    	 */
    	public ResourceEditorRegistrar(ResourceLoader resourceLoader, PropertyResolver propertyResolver) {
    		this.resourceLoader = resourceLoader;
    		this.propertyResolver = propertyResolver;
    	}
    
    
    	/**
    	 * Populate the given {@code registry} with the following resource editors:
    	 * ResourceEditor, InputStreamEditor, InputSourceEditor, FileEditor, URLEditor,
    	 * URIEditor, ClassEditor, ClassArrayEditor.
    	 */
    	@Override
    	public void registerCustomEditors(PropertyEditorRegistry registry) {
    		ResourceEditor baseEditor = new ResourceEditor(this.resourceLoader, this.propertyResolver);
    		doRegisterEditor(registry, Resource.class, baseEditor);
    		doRegisterEditor(registry, ContextResource.class, baseEditor);
    		doRegisterEditor(registry, InputStream.class, new InputStreamEditor(baseEditor));
    		doRegisterEditor(registry, InputSource.class, new InputSourceEditor(baseEditor));
    		doRegisterEditor(registry, File.class, new FileEditor(baseEditor));
    		if (pathClass != null) {
    			doRegisterEditor(registry, pathClass, new PathEditor(baseEditor));
    		}
    		doRegisterEditor(registry, Reader.class, new ReaderEditor(baseEditor));
    		doRegisterEditor(registry, URL.class, new URLEditor(baseEditor));
    
    		ClassLoader classLoader = this.resourceLoader.getClassLoader();
    		doRegisterEditor(registry, URI.class, new URIEditor(classLoader));
    		doRegisterEditor(registry, Class.class, new ClassEditor(classLoader));
    		doRegisterEditor(registry, Class[].class, new ClassArrayEditor(classLoader));
    
    		if (this.resourceLoader instanceof ResourcePatternResolver) {
    			doRegisterEditor(registry, Resource[].class,
    					new ResourceArrayPropertyEditor((ResourcePatternResolver) this.resourceLoader, this.propertyResolver));
    		}
    	}
    
    	/**
    	 * Override default editor, if possible (since that's what we really mean to do here);
    	 * otherwise register as a custom editor.
    	 */
    	private void doRegisterEditor(PropertyEditorRegistry registry, Class<?> requiredType, PropertyEditor editor) {
    		if (registry instanceof PropertyEditorRegistrySupport) {
    			((PropertyEditorRegistrySupport) registry).overrideDefaultEditor(requiredType, editor);
    		}
    		else {
    			registry.registerCustomEditor(requiredType, editor);
    		}
    	}
    
    }

### 2.3 CustomEditorConfigurer ###

可以自定义PropertyEditorRegistry、PropertyEditor，它其实是一个BeanFactoryPostProcessor

public class CustomEditorConfigurer implements BeanFactoryPostProcessor, Ordered {
    
    	protected final Log logger = LogFactory.getLog(getClass());
    
    	private int order = Ordered.LOWEST_PRECEDENCE;  // default: same as non-Ordered
    
    	private PropertyEditorRegistrar[] propertyEditorRegistrars;
    
    	private Map<Class<?>, Class<? extends PropertyEditor>> customEditors;
    
    
    	public void setOrder(int order) {
    		this.order = order;
    	}
    
    	@Override
    	public int getOrder() {
    		return this.order;
    	}
    	public void setPropertyEditorRegistrars(PropertyEditorRegistrar[] propertyEditorRegistrars) {
    		this.propertyEditorRegistrars = propertyEditorRegistrars;
    	}
    	public void setCustomEditors(Map<Class<?>, Class<? extends PropertyEditor>> customEditors) {
    		this.customEditors = customEditors;
    	}
        
        //beanFactory中添加PropertyEditorRegistrar和PropertyEditor
    	@Override
    	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
    		if (this.propertyEditorRegistrars != null) {
    			for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) {
    				beanFactory.addPropertyEditorRegistrar(propertyEditorRegistrar);
    			}
    		}
    		if (this.customEditors != null) {
    			for (Map.Entry<Class<?>, Class<? extends PropertyEditor>> entry : this.customEditors.entrySet()) {
    				Class<?> requiredType = entry.getKey();
    				Class<? extends PropertyEditor> propertyEditorClass = entry.getValue();
    				beanFactory.registerCustomEditor(requiredType, propertyEditorClass);
    			}
    		}
    	}
    }

### 2.4 PropertyAccessor和BeanWrapper ###

PropertyAccessor接口定义了各种访问属性的方法。

*  BeanWrapperImpl，对属性取值赋值依赖 setter/getter方法，必须通过readMethod.invoke等反射方式进行，遵循javabean规约
 *  DirectFieldAccessor，4.1版本中引入，执行直接字段访问而不是通过Java Bean的getter（效率更高，特别是实现嵌套遍历字段），在springmvc中有@Validated和BindingResult bindingResult是配对出现，实际就是通过[DataBinder][].getBindingResult()填充，真正是由DirectFieldBindingResult完成的。

@RequestMapping(value = "/addStudent", method = RequestMethod.POST)
    public String addStudent(@ModelAttribute("student") @Validated Student student,
       BindingResult bindingResult, Model model) {
       if (bindingResult.hasErrors()) {
          return "student";
       }
       model.addAttribute("name", student.getName());
       model.addAttribute("age", student.getAge());
       model.addAttribute("id", student.getId());
       return "student_result";
    }

BeanWrapper接口还继承了PropertyAccessor, propertyEditorRegistry, TypeConverter、ConfigurablePropertyAccessor接口，所以它是一个功能强大的综合体。

> /\*\*  
>  \* The central interface of Spring's low-level JavaBeans infrastructure.  
>  \*  
>  \* <p>Typically not used directly but rather implicitly via a  
>  \* \{@link org.springframework.beans.factory.BeanFactory\} or a  
>  \* \{@link org.springframework.validation.DataBinder\}.  
>  \*/
> 
> BeanWrapper是spring中对JavaBeans遵循的规约，间接服务于BeanFactory和[DataBinder][]

![20190326203300932.png][]

![20190326210147985.png][]

![20190326203457180.png][]

private static class GetterBean {
       private String name;
       public void setName(String name) {
          this.name = name;
       }
       public String getName() {
          if (this.name == null) {
             throw new RuntimeException("name property must be set");
          }
          return name;
       }
    }
    //BeanWrapperImpl
    @Test
    public void setterDoesNotCallGetter() {
       GetterBean target = new GetterBean();
       BeanWrapper accessor = new BeanWrapperImpl(target);
       accessor.setPropertyValue("name", "tom");
       assertTrue("Set name to tom", target.getName().equals("tom"));
    }
    //DirectFieldAccessor
    @Test
    public void setterDoesNotCallGetter() {
    	TestBean bean = new TestBean() {
                @SuppressWarnings("unused")
                String name = "alex";
        };
       //嵌套设置/访问对象字段数据
       DirectFieldAccessor accessor = new DirectFieldAccessor(bean);
       //如果嵌套对象为null，字段创建
       accessor.setAutoGrowNestedPaths(true);
       //设置字段值
       accessor.setPropertyValue("name", "zhangsan");
       //读取字段值
       System.out.println(accessor.getPropertyValue("name"));
    }

总结，springBean其实是集成拓展了javaBean的内省解决方案，但在它的基础上做了增强。![DataBinder][]

[Link 1]: https://blog.csdn.net/alex_xfboy/article/category/8125275
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2l0c29mdGNoZW5mZWk_size_16_color_FFFFFF_t_70 1]: /images/20220403/532ebe4e12f24a12a50a23b1b1b0a978.png
[DataBinder]: /images/20220403/f79d07a6e8114a758fd2c34e63ba9bfb.png
[20190326203300932.png]: /images/20220403/ef311045e2fa4d69b1cb0ee05eaa0707.png
[20190326210147985.png]: /images/20220403/efb9bb04d6534dc6a51fc9063458bed2.png
[20190326203457180.png]: /images/20220403/92eaab68c2894c8d975a715436b95410.png