spring中自定义属性编辑器如何注入和取出的流程(通过CustomEditorConfigurer)

柔光的暖阳◎ 2021-12-04 07:53 267阅读 0赞

我们可以自定义属性编辑器对类中的实例对象赋值，通过string类型值转换成对象类型值进行赋值。当我们使用下列方式注册时：

上面方式把我们自己定义的属性编辑器renchaofeng\_propertyEditor.TestPropertyEditor注入到org.springframework.beans.factory.config.CustomEditorConfigurer的customEditors属性中，就可以达到转换的效果，那么原理流程是怎样的呢？如下：

org.springframework.beans.factory.config.CustomEditorConfigurer实现了BeanFactoryPostProcessor接口，所以会实现postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)方法，在此方法中代码如下：

public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
    		if (this.propertyEditorRegistrars != null) {
    			for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) {
    				beanFactory.addPropertyEditorRegistrar(propertyEditorRegistrar);
    			}
    		}
    		if (this.customEditors != null) {//此处集合customEditors中有我们的属性编辑器renchaofeng_propertyEditor.TestPropertyEditor
    			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);//把我们自定义属性编辑器注册入beanFactory中以备后续使用
    			}
    		}
    	}

上面是注入过程，下面在什么怎么取出使用呢？答案如下：　在bean的实例化过程中使用，在AbstractBeanFactory类中创建bean方法中，如下：

@SuppressWarnings("unchecked")
    	protected <T> T doGetBean(
    			final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
    			throws BeansException {
    //......前面源码省略.....
    // Check if required type matches the type of the actual bean instance.
    		if (requiredType != null && bean != null && !requiredType.isInstance(bean)) {
    			try {
    				return getTypeConverter().convertIfNecessary(bean, requiredType);//在此处进行获取我们自定义属性编辑器
    			}
    			catch (TypeMismatchException ex) {
    				if (logger.isDebugEnabled()) {
    					logger.debug("Failed to convert bean '" + name + "' to required type '" +
    							ClassUtils.getQualifiedName(requiredType) + "'", ex);
    				}
    				throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
    			}
    		}
    		return (T) bean;
    	}

进入convertIfNecessary中一路点击下去进入类TypeConverterSupport中的方法doConvert，如下：

private <T> T doConvert(Object value, Class<T> requiredType, MethodParameter methodParam, Field field)
    			throws TypeMismatchException {
    		try {
    			if (field != null) {
    				return this.typeConverterDelegate.convertIfNecessary(value, requiredType, field);
    			}
    			else {
    				return this.typeConverterDelegate.convertIfNecessary(value, requiredType, methodParam);//通过此方法进入点击进去
    			}
    		}
    		catch (ConverterNotFoundException ex) {
    			throw new ConversionNotSupportedException(value, requiredType, ex);
    		}
    		catch (ConversionException ex) {
    			throw new TypeMismatchException(value, requiredType, ex);
    		}
    		catch (IllegalStateException ex) {
    			throw new ConversionNotSupportedException(value, requiredType, ex);
    		}
    		catch (IllegalArgumentException ex) {
    			throw new TypeMismatchException(value, requiredType, ex);
    		}
    	}

点击进去进入类TypeConverterDelegate中找到方法convertIfNecessary，如下：

/**
    	 * Convert the value to the required type (if necessary from a String),
    	 * for the specified property.
    	 * @param propertyName name of the property
    	 * @param oldValue the previous value, if available (may be {@code null})
    	 * @param newValue the proposed new value
    	 * @param requiredType the type we must convert to
    	 * (or {@code null} if not known, for example in case of a collection element)
    	 * @param typeDescriptor the descriptor for the target property or field
    	 * @return the new value, possibly the result of type conversion
    	 * @throws IllegalArgumentException if type conversion failed
    	 */
    	@SuppressWarnings("unchecked")
    	public <T> T convertIfNecessary(String propertyName, Object oldValue, Object newValue,
    			Class<T> requiredType, TypeDescriptor typeDescriptor) throws IllegalArgumentException {
    // Custom editor for this type?
    		PropertyEditor editor = this.propertyEditorRegistry.findCustomEditor(requiredType, propertyName);//此处就会查找取出我们自定义的属性编辑器进行使用
    
    		ConversionFailedException conversionAttemptEx = null;
    
    		// No custom editor but custom ConversionService specified?
    		ConversionService conversionService = this.propertyEditorRegistry.getConversionService();
    		if (editor == null && conversionService != null && newValue != null && typeDescriptor != null) {
    			TypeDescriptor sourceTypeDesc = TypeDescriptor.forObject(newValue);
    			if (conversionService.canConvert(sourceTypeDesc, typeDescriptor)) {
    				try {
    					return (T) conversionService.convert(newValue, sourceTypeDesc, typeDescriptor);
    				}
    				catch (ConversionFailedException ex) {
    					// fallback to default conversion logic below
    					conversionAttemptEx = ex;
    				}
    			}
    		}
    
    		Object convertedValue = newValue;
    //.....后面源码省略。。。。。
    }

通过debug调试取出我们的属性编辑器如下：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzQwNzE4MTY4_size_16_color_FFFFFF_t_70][]

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