spring中类型转换器的注入和取出流程(通过ConversionServiceFactoryBean方式注入)

傷城~ 2021-12-03 23:35 268阅读 0赞

package renchaofeng_conversionService;
    
    import java.util.Date;
    
    public class User {
    	private String loginname;
    	private Date birthday;//需要赋值的Date类型属性值
    	public String getLoginname() {
    		return loginname;
    	}
    	public void setLoginname(String loginname) {
    		this.loginname = loginname;
    	}
    	public Date getBirthday() {
    		return birthday;
    	}
    	public void setBirthday(Date birthday) {
    		this.birthday = birthday;
    	}
    	@Override
    	public String toString() {
    		return "User [loginname=" + loginname + ", birthday=" + birthday + "]";
    	}
    }

package renchaofeng_conversionService;
    
    import java.text.ParseException;
    import java.text.SimpleDateFormat;
    import java.util.Date;
    
    import org.springframework.core.convert.converter.Converter;
    
    public class StringToDateConverter implements Converter<String,Date>{//定义类型转换器
       private String datePattern;
       
    	public void setDatePattern(String datePattern) {
    	    this.datePattern = datePattern;
        }
    
    	@Override
    	public Date convert(String source) {
    		SimpleDateFormat sdf = new SimpleDateFormat(this.datePattern);
    		try {
    			return sdf.parse(source);
    		} catch (ParseException e) {
    			e.printStackTrace();
    		}
    		return null;
    	}
    
    }

如上方式，就可以把字符串值2019-07-17赋值给User中的Date类型变量birthday。

那么类型转换器何时被注入容器和取出使用的时机流程是什么呢？请看下面分析：

在容器初始化bean时会调用类AbstractApplicationContext中的finishBeanFactoryInitialization方法，源码如下：

/**
    	 * Finish the initialization of this context's bean factory,
    	 * initializing all remaining singleton beans.
    	 */
    	protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
    		// Initialize conversion service for this context.
    		if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
    				beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {//找到我们配置在spring配置文件中的conversionService类进行加载，至此注入成功
    			beanFactory.setConversionService(
    					beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
    		}
    
    		// Register a default embedded value resolver if no bean post-processor
    		// (such as a PropertyPlaceholderConfigurer bean) registered any before:
    		// at this point, primarily for resolution in annotation attribute values.
    		if (!beanFactory.hasEmbeddedValueResolver()) {
    			beanFactory.addEmbeddedValueResolver(new StringValueResolver() {
    				@Override
    				public String resolveStringValue(String strVal) {
    					return getEnvironment().resolvePlaceholders(strVal);
    				}
    			});
    		}
    
    		// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
    		String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    		for (String weaverAwareName : weaverAwareNames) {
    			getBean(weaverAwareName);
    		}
    
    		// Stop using the temporary ClassLoader for type matching.
    		beanFactory.setTempClassLoader(null);
    
    		// Allow for caching all bean definition metadata, not expecting further changes.
    		beanFactory.freezeConfiguration();
    
    		// Instantiate all remaining (non-lazy-init) singletons.
    		beanFactory.preInstantiateSingletons();
    	}

下面看取出conversionService过程：获取在类TypeConverterDelegate中，从AbstractBeanFactory类中的377行

/**
    	 * 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);
    
    		ConversionFailedException conversionAttemptEx = null;
    
    		// No custom editor but custom ConversionService specified?
    		ConversionService conversionService = this.propertyEditorRegistry.getConversionService();//此处取出使用
    		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;
    				}
    			}
    		}
    //.......下面代码省略...
    ｝