探秘 Spring 的 PropertyEditor

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探秘 Spring 的 PropertyEditor

PropertyEditor & PropertyEditorSupport 介绍

java.beans.PropertyEditor 是 JDK 自带的类，是提供给 AWT。作啥用呢、就是讲用户在图形见面中输入的字符串转换位对应类型的值(对象)。相似于一个 convertor。

public interface PropertyEditor {
  void setValue(Object value);   Object getValue();   boolean isPaintable();   String getJavaInitializationString();   String getAsText();   void setAsText(String text) throws java.lang.IllegalArgumentException;   String[] getTags();   java.awt.Component getCustomEditor();   boolean supportsCustomEditor();   void addPropertyChangeListener(PropertyChangeListener listener);   void removePropertyChangeListener(PropertyChangeListener listener);  } 复制代码

主要方法有四个

• void setValue(Object value); 设置属性值
• Object getValue(); 获取属性值
• String getAsText(); 把属性值转换成 String
• void setAsText(String text); 把 String 转换成属性值

而 Java 也为咱们提供了一个默认的实现类 java.beans.PropertyEditorSupport

private Object value;
public void setValue(Object value) {  this.value = value;  firePropertyChange(); }  public Object getValue() {  return value; } public void setAsText(String text) throws java.lang.IllegalArgumentException {  if (value instanceof String) {  setValue(text);  return;  }  throw new java.lang.IllegalArgumentException(text); } public String getAsText() {  return (this.value != null)  ? this.value.toString()  : null; } 复制代码

咱们只要重写 setAsText 和 getAsText 方法能够实现 String 类型到特定类型的转换了

与 Spring 的关系

说了那么久、这个跟 Spring 有什么锤子关系吗 ?

咱们想想、当你使用 xml 配置文件给某个属性设定某个值的时候、咱们输入的是否是一个字符串、可是咱们对应的这个属性的类型却不必定是字符串类型、这种场景之下、是否是跟 AWT 的场景是同样的。因此 Spring 的属性解释都是继承自 PropertyEditorSupport 而后重写了 setAsText 和 getAsText

举个例子

public class CustomBooleanEditor extends PropertyEditorSupport {
  public static final String VALUE_TRUE = "true";   public static final String VALUE_FALSE = "false";   public static final String VALUE_ON = "on";   public static final String VALUE_OFF = "off";   public static final String VALUE_YES = "yes";   public static final String VALUE_NO = "no";   public static final String VALUE_1 = "1";   public static final String VALUE_0 = "0";   // 为 true 的时候的字符串、默认为 null  @Nullable  private final String trueString;   // 为 false 的时候的字符串、默认为 null  @Nullable  private final String falseString;  // 是否容许为 null   // 基本类型 boolean 的时候不容许空的字符串  // 引用类型 Boolean 的时候容许空的字符串  private final boolean allowEmpty;    public CustomBooleanEditor(boolean allowEmpty) {  this(null, null, allowEmpty);  }   public CustomBooleanEditor(@Nullable String trueString, @Nullable String falseString, boolean allowEmpty) {  this.trueString = trueString;  this.falseString = falseString;  this.allowEmpty = allowEmpty;  }    @Override  public void setAsText(@Nullable String text) throws IllegalArgumentException {   String input = (text != null ? text.trim() : null);   if (this.allowEmpty && !StringUtils.hasLength(input)) {  // Treat empty String as null value.  setValue(null);  } else if (this.trueString != null && this.trueString.equalsIgnoreCase(input)) {  setValue(Boolean.TRUE);  } else if (this.falseString != null && this.falseString.equalsIgnoreCase(input)) {  setValue(Boolean.FALSE);  } else if (this.trueString == null &&  (VALUE_TRUE.equalsIgnoreCase(input) || VALUE_ON.equalsIgnoreCase(input) ||  VALUE_YES.equalsIgnoreCase(input) || VALUE_1.equals(input))) {  setValue(Boolean.TRUE);  } else if (this.falseString == null &&  (VALUE_FALSE.equalsIgnoreCase(input) || VALUE_OFF.equalsIgnoreCase(input) ||  VALUE_NO.equalsIgnoreCase(input) || VALUE_0.equals(input))) {  setValue(Boolean.FALSE);  } else {  throw new IllegalArgumentException("Invalid boolean value [" + text + "]");  }  }   @Override  public String getAsText() {  if (Boolean.TRUE.equals(getValue())) {  return (this.trueString != null ? this.trueString : VALUE_TRUE);  } else if (Boolean.FALSE.equals(getValue())) {  return (this.falseString != null ? this.falseString : VALUE_FALSE);  } else {  return "";  }  }  } 复制代码

方法也是挺简单的就不啰嗦解释了

举个例子

public class Job {
  private boolean completed;   private Boolean started;  // get and set ........... } 复制代码

<bean class="com.demo.property.editor.Job" id="job">
 <property name="completed" value="on" />  <property name="started" value=""/> </bean> 复制代码

获取这个 bean 并打印 Job{completed=true, started=null}

相关组件介绍

PropertyEditorRegistry

一看名字就知道是一个注册的接口

void registerCustomEditor(Class<?> requiredType, PropertyEditor propertyEditor);
 void registerCustomEditor(@Nullable Class<?> requiredType, @Nullable String propertyPath, PropertyEditor propertyEditor);  @Nullable PropertyEditor findCustomEditor(@Nullable Class<?> requiredType, @Nullable String propertyPath); 复制代码

PropertyEditorRegistrySupport

PropertyEditorRegistry 的实现类。当咱们尝试去经过 Class 对象获取对应的 PropertyEditor 的时候、它会为咱们初始化一系列默认的 PropertyEditor

在 doCreateBean 的 populateBean 中会调用 getDefaultEditor 获取对应的 PropertyEditor 进行值的类型转换

// spring 默认提供的 propertyEditor
@Nullable private Map<Class<?>, PropertyEditor> defaultEditors;  // 去覆盖的 默认的 property editor @Nullable private Map<Class<?>, PropertyEditor> overriddenDefaultEditors;  // 自定义的一些 property editor @Nullable private Map<Class<?>, PropertyEditor> customEditors;  // 属性的路径/属性名，CustomEditorHolder 包含的是 Class 和 PropertyEditor @Nullable private Map<String, CustomEditorHolder> customEditorsForPath;  // 若是注册的父 class、那么子类的 class 找不到的时候、就会返回这个父的 class 而且讲这个关系保存在 // 这个 map 中 @Nullable private Map<Class<?>, PropertyEditor> customEditorCache;  @Nullable  public PropertyEditor getDefaultEditor(Class<?> requiredType) {  if (!this.defaultEditorsActive) {  return null;  }  if (this.overriddenDefaultEditors != null) {  PropertyEditor editor = this.overriddenDefaultEditors.get(requiredType);  if (editor != null) {  return editor;  }  }  if (this.defaultEditors == null) {  createDefaultEditors();  }  return this.defaultEditors.get(requiredType);  }   private void createDefaultEditors() {  this.defaultEditors = new HashMap<>(64);   // Simple editors, without parameterization capabilities.  // The JDK does not contain a default editor for any of these target types.  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());  this.defaultEditors.put(Path.class, 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());  this.defaultEditors.put(ZoneId.class, new ZoneIdEditor());   // 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));   // Only register config value editors if explicitly requested.  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);  }  } 复制代码

BeanWrapper

Spring 中用于封装 bean 的是 BeanWrapper 类型、而它又间接继承了 PropertyEditorRegistry。BeanWrapperImpl 是 BeanWrapper 的实现类、咱们在系统中看到的大多数 PropertyEditorRegistry 都是 BeanWrapperImpl 的对象。BeanWrapperImpl 还继承了 PropertyEditorRegistrySupport 这个实现类

PropertyEditorRegistrar

property editor 的登记处

void registerCustomEditors(PropertyEditorRegistry registry);
复制代码

ResourceEditorRegistrar

惟一的一个默认的实现类

public class ResourceEditorRegistrar implements PropertyEditorRegistrar {
  private final PropertyResolver propertyResolver;   private final ResourceLoader resourceLoader;   public ResourceEditorRegistrar(ResourceLoader resourceLoader, PropertyResolver propertyResolver) {  this.resourceLoader = resourceLoader;  this.propertyResolver = propertyResolver;  }   @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));  doRegisterEditor(registry, Path.class, 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));  }  }   private void doRegisterEditor(PropertyEditorRegistry registry, Class<?> requiredType, PropertyEditor editor) {  if (registry instanceof PropertyEditorRegistrySupport) {  ((PropertyEditorRegistrySupport) registry).overrideDefaultEditor(requiredType, editor);  }  else {  registry.registerCustomEditor(requiredType, editor);  }  }  } 复制代码

先说下这个类被使用到的地方吧、只有使用 ApplicationContext 的时候这个 Registrar 才会被使用到、上面的 PropertyEditor 才会去注册或者覆盖 PropertyEditorRegistry 默认的值

调用关系链为

ClassPathXmlApplicationContext 构造函数 -> refresh -> prepareBeanFactory() -> 建立 ResourceEditorRegistrar 增长到 Set 中
复制代码

继而它会在 doCreateBean 的 createBeanInstance 中将 ResourceEditorRegistrar 的默认的 PropertyEditor 注册进去

例子

public class Job {
  private boolean completed;   private Content content;  // get and set method } 复制代码

public class Content {
 private String details;  private String type;  private int priority;  // get and set method } 复制代码

<bean class="com.demo.property.editor.Job" id="job" lazy-init="true">
 <property name="completed" value="off" />  <property name="content" value="关注我:紧急:100"/> </bean> 复制代码

ClassPathXmlApplicationContext classPathXmlApplicationContext =
 new ClassPathXmlApplicationContext("property.editor/coderLi.xml");  classPathXmlApplicationContext.getBeanFactory().addPropertyEditorRegistrar(registry -> {  if (registry instanceof PropertyEditorRegistrySupport) {  ((PropertyEditorRegistrySupport) registry).overrideDefaultEditor(Content.class, new ContentPropertyEditor());  System.out.println("PropertyEditorRegistrySupport");  } else {  registry.registerCustomEditor(Content.class, new ContentPropertyEditor());  } });   Object job = classPathXmlApplicationContext.getBean("job"); System.out.println(job); 复制代码

实现相同效果的方法有不少、好比说 CustomEditorConfigurer、也能够实现 BeanFactoryPostProcessor 接口等等

如我上面的代码实现的话、注意一个点就是、这个 bean 必须是一个延迟实例化的、由于 ApplicationContext 默认是会将全部的非 lazy 的 bean 实例化、而这个时候咱们的 PropertyEditor 尚未注册进去、将会报错

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