Spring3.2 bug 嵌套context:property-placeholder替换的java.lang.StackOverflowError异常分析

相信很多朋友都使用过如下代码进行可变数据的占位符替换。

 

<context:property-placeholder location="classpath:resources.properties" ignore-unresolvable="true"/>

最近使用maven profile + maven资源过滤 + spring3.2进行开发，如果不小心忘了maven的资源过滤，或者如遇到这种abc=${bcd} 这种循环引用时，且bcd不存在时，即：

 

如果代码中引用如abc：

 

@Value("${abc}")
private String abc;

 且您的配置文件出现如下情况：

 

 

abc=${dce} ----->嵌套引用dce属性

dce=${none} --->此时none不存在

 

如果在spring3.1中，并配置了ignore-unresolvable，那么直接返回${none}，而不会在spring3.2中会遇到如下异常（spring3.1不会遇到问题）：

 

java.lang.StackOverflowError
	at java.security.AccessController.doPrivileged(Native Method)
	at com.sun.naming.internal.VersionHelper12.getJndiProperties(VersionHelper12.java:106)
	at com.sun.naming.internal.ResourceManager.getInitialEnvironment(ResourceManager.java:202)
	at javax.naming.InitialContext.init(InitialContext.java:238)
	at javax.naming.InitialContext.<init>(InitialContext.java:216)
	at org.springframework.jndi.JndiTemplate.createInitialContext(JndiTemplate.java:136)
	at org.springframework.jndi.JndiTemplate.getContext(JndiTemplate.java:103)
	at org.springframework.jndi.JndiTemplate.execute(JndiTemplate.java:85)
	at org.springframework.jndi.JndiTemplate.lookup(JndiTemplate.java:152)
	at org.springframework.jndi.JndiTemplate.lookup(JndiTemplate.java:178)
	at org.springframework.jndi.JndiLocatorSupport.lookup(JndiLocatorSupport.java:95)
	at org.springframework.jndi.JndiLocatorDelegate.lookup(JndiLocatorDelegate.java:38)
	at org.springframework.jndi.JndiLocatorSupport.lookup(JndiLocatorSupport.java:77)
	at org.springframework.jndi.JndiLocatorDelegate.lookup(JndiLocatorDelegate.java:33)
	at org.springframework.jndi.JndiPropertySource.getProperty(JndiPropertySource.java:82)
	at org.springframework.core.env.PropertySourcesPropertyResolver.getProperty(PropertySourcesPropertyResolver.java:73)
	at org.springframework.core.env.PropertySourcesPropertyResolver.getProperty(PropertySourcesPropertyResolver.java:59)
	at org.springframework.core.env.AbstractEnvironment.getProperty(AbstractEnvironment.java:427)
	at org.springframework.context.support.PropertySourcesPlaceholderConfigurer$1.getProperty(PropertySourcesPlaceholderConfigurer.java:131)
	at org.springframework.context.support.PropertySourcesPlaceholderConfigurer$1.getProperty(PropertySourcesPlaceholderConfigurer.java:128)
	at org.springframework.core.env.PropertySourcesPropertyResolver.getProperty(PropertySourcesPropertyResolver.java:73)
	at org.springframework.core.env.PropertySourcesPropertyResolver.getProperty(PropertySourcesPropertyResolver.java:59)
	at org.springframework.core.env.AbstractPropertyResolver$1.resolvePlaceholder(AbstractPropertyResolver.java:176)
	at org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:146)
	at org.springframework.util.PropertyPlaceholderHelper.replacePlaceholders(PropertyPlaceholderHelper.java:125)

 

其实就是死循环了，造成栈溢出。 

 

源码分析：

1、<context:property-placeholder> 实际使用的是org.springframework.context.support.PropertySourcesPlaceholderConfigurer，其是一个BeanFactory后处理器（BeanFactoryPostProcessor）：

 

protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
			final ConfigurablePropertyResolver propertyResolver) throws BeansException {

		propertyResolver.setPlaceholderPrefix(this.placeholderPrefix);
		propertyResolver.setPlaceholderSuffix(this.placeholderSuffix);
		propertyResolver.setValueSeparator(this.valueSeparator);

		StringValueResolver valueResolver = new StringValueResolver() {
			public String resolveStringValue(String strVal) {
				String resolved = ignoreUnresolvablePlaceholders ?
						propertyResolver.resolvePlaceholders(strVal) :
						propertyResolver.resolveRequiredPlaceholders(strVal);
				return (resolved.equals(nullValue) ? null : resolved);
			}
		};

		doProcessProperties(beanFactoryToProcess, valueResolver);
	}

 1.1、此处根据ignoreUnresolvablePlaceholders(<context:property-placeholder>中的ignore-unresolvable)决定是否必须查找到占位符的值，

 

public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
    ………………
    this.processProperties(beanFactory, new PropertySourcesPropertyResolver(this.propertySources));
}

1.2、最后一行直接委托给了processProperties方法 并传入了PropertySourcesPropertyResolver，这个是核心，问题就出在这；

1.3、然后不管propertyResolver.propertyResolver.resolvePlaceholders还是propertyResolver.resolveRequiredPlaceholders都会调用：

return doResolvePlaceholders(text, strictHelper/nonStrictHelper);

只是此处一个使用严格的PropertyPlaceholderHelper 另一个是不严格的PropertyPlaceholderHelper；

private String doResolvePlaceholders(String text, PropertyPlaceholderHelper helper) {
    return helper.replacePlaceholders(text, new PlaceholderResolver() {
       public String resolvePlaceholder(String placeholderName) {
           return getProperty(placeholderName);
       }
    });
}

1.4、 此时调用helper的

public String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) {
    Assert.notNull(value, "Argument 'value' must not be null.");
    return parseStringValue(value, placeholderResolver, new HashSet<String>());
}

1.5、parseStringValue方法：

如果发现如abc=${dce}，那么会接着调用如下代码接着循环找值

String propVal = placeholderResolver.resolvePlaceholder(placeholder);

1.6、最终会调用1.3中的getProperty方法去获取值，即此时key是dce：

public String getProperty(String key) {
    if (logger.isTraceEnabled()) {
        logger.trace(format("getProperty(\"%s\") (implicit targetType [String])", key));
    }
    return this.getProperty(key, String.class);
}

 最终会调用：

if (String.class.equals(valueType)) {
    value = this.resolveNestedPlaceholders((String) value);
}

 

1.7、到了resolveNestedPlaceholders

protected String resolveNestedPlaceholders(String value) {
    return this.ignoreUnresolvableNestedPlaceholders ?
            this.resolvePlaceholders(value) :
            this.resolveRequiredPlaceholders(value);
}

 问题出现了：如果此处的ignoreUnresolvableNestedPlaceholders为false，那么接着又去了resolveRequiredPlaceholders，此是就会死循环问题，spring3.2没有考虑这个问题，所以会造成java.lang.StackOverflowError。

 

解决方案：

1、spring考虑此循环引用的问题

2、在org.springframework.context.support.PropertySourcesPlaceholderConfigurer中在new PropertySourcesPropertyResolver(this.propertySources)后调用其setIgnoreUnresolvableNestedPlaceholders(ignoreUnresolvablePlaceholders)，把ignoreUnresolvablePlaceholders传入即可。

 

到此分析结束。

 

 

评论

1 楼 85977328 2013-05-14  

经常看到开涛的文章，顶～