记一次踩坑:springboot2.0.2配置fastjson不生效

最近在尝试搭建springboot+dubbo+shiro基于注解的一个项目,突发奇想一想把消息转换器从jackson换成fastjson,因而就开始了折腾之路.

轻车熟路的去自定了一个SpringMvcConfigure去继承WebMvcConfigurerAdapter,而后就发现这个WebMvcConfigurerAdapter居然过期了?what?点进去看源码:

/**
 * An implementation of {@link WebMvcConfigurer} with empty methods allowing
 * subclasses to override only the methods they're interested in.
 *
 * @author Rossen Stoyanchev
 * @since 3.1
 * @deprecated as of 5.0 {@link WebMvcConfigurer} has default methods (made
 * possible by a Java 8 baseline) and can be implemented directly without the
 * need for this adapter
 */
@Deprecated
public abstract class WebMvcConfigurerAdapter implements WebMvcConfigurer {}

能够看到从spring5.0开始就被@Deprecated,原来是java8中支持接口中有默认方法,因此咱们如今能够直接实现WebMvcConfigurer,而后选择性的去重写某个方法,而不用实现它的全部方法.

因而就实现了WebMvcConfigurer:

@Configuration
public class SpringMvcConfigure implements WebMvcConfigurer {

    /**
     * 配置消息转换器
     * @param converters
     */
    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();
        //自定义配置...
        FastJsonConfig config = new FastJsonConfig();
        config.setSerializerFeatures(SerializerFeature.QuoteFieldNames,
                SerializerFeature.WriteEnumUsingToString,
                /*SerializerFeature.WriteMapNullValue,*/
                SerializerFeature.WriteDateUseDateFormat,
                SerializerFeature.DisableCircularReferenceDetect);
        fastJsonHttpMessageConverter.setFastJsonConfig(config);
        converters.add(fastJsonHttpMessageConverter);
    }

}

本觉得这样子配置就能够完事儿,可是诡异的事情发生了,我明明注释了SerializerFeature.WriteMapNullValue,但是返回的json中仍然有为null的字段,而后我就去com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter中的write和writeInternal打了断点,再次执行,居然什么都没有发生,根本没有走这两个方法,因而在自定义的SpringMvcConfigure中configureMessageConverters方法内打了断点,想看看这个方法参数converters里边到底有什么:

看到这里就想到,确定是我本身添加的fastjson在后边,因此没有生效,因此就加了如下代码:

@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    converters = converters.stream()
                .filter((converter)-> !(converter instanceof MappingJackson2HttpMessageConverter))
                .collect(Collectors.toList());
    FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();
    //自定义配置...
    FastJsonConfig config = new FastJsonConfig();
    config.setSerializerFeatures(SerializerFeature.QuoteFieldNames,
            SerializerFeature.WriteEnumUsingToString,
            /*SerializerFeature.WriteMapNullValue,*/
            SerializerFeature.WriteDateUseDateFormat,
            SerializerFeature.DisableCircularReferenceDetect);
    fastJsonHttpMessageConverter.setFastJsonConfig(config);
    converters.add(fastJsonHttpMessageConverter);
}

居然尚未生效,后来开始追踪,开始方法是从org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport类中的一个bean配置:

@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {
    RequestMappingHandlerAdapter adapter = createRequestMappingHandlerAdapter();
    adapter.setContentNegotiationManager(mvcContentNegotiationManager());
    //就是从这里开始设置converters的,而后从这里一路追踪下去.
    adapter.setMessageConverters(getMessageConverters());
    adapter.setWebBindingInitializer(getConfigurableWebBindingInitializer());
    adapter.setCustomArgumentResolvers(getArgumentResolvers());
    adapter.setCustomReturnValueHandlers(getReturnValueHandlers());

    if (jackson2Present) {
        adapter.setRequestBodyAdvice(Collections.singletonList(new JsonViewRequestBodyAdvice()));
        adapter.setResponseBodyAdvice(Collections.singletonList(new JsonViewResponseBodyAdvice()));
    }

    AsyncSupportConfigurer configurer = new AsyncSupportConfigurer();
    configureAsyncSupport(configurer);
    if (configurer.getTaskExecutor() != null) {
        adapter.setTaskExecutor(configurer.getTaskExecutor());
    }
    if (configurer.getTimeout() != null) {
        adapter.setAsyncRequestTimeout(configurer.getTimeout());
    }
    adapter.setCallableInterceptors(configurer.getCallableInterceptors());
    adapter.setDeferredResultInterceptors(configurer.getDeferredResultInterceptors());

    return adapter;
}

getMessageConverters()方法:

protected final List<HttpMessageConverter<?>> getMessageConverters() {
    if (this.messageConverters == null) {
        this.messageConverters = new ArrayList<>();
        configureMessageConverters(this.messageConverters);//进入这一步
        if (this.messageConverters.isEmpty()) {
            addDefaultHttpMessageConverters(this.messageConverters);
        }
        extendMessageConverters(this.messageConverters);
    }
    return this.messageConverters;
}

org.springframework.web.servlet.config.annotation.DelegatingWebMvcConfiguration:

@Override
protected void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    this.configurers.configureMessageConverters(converters);
}
@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    for (WebMvcConfigurer delegate : this.delegates) {
        delegate.configureMessageConverters(converters);
    }
}

this.delegates包含了springboot的一个默认配置类类:org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration里边有一个参数

private final HttpMessageConverters messageConverters;

for循环里的delegate.configureMessageConverters(converters)调用了WebMvcAutoConfiguration中的configureMessageConverters方法:

@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    converters.addAll(this.messageConverters.getConverters());
}

执行完这个后,就给converters中添加了10个转换器了,就是上图中的10个.
this.delegates中还有一个就是咱们自定义的那个,执行完后,在咱们自定义的那个SpringMvcConfigure发现我添加的fastjson添加进去了,可是org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport.getMessageConverters(),发现converters并无发现咱们添加进去的FastJsonHttpMessageConverter,这时忽然又想起来:java8的stream api每次都是生成一个新的对象,因此致使converters已经不是传递过来的那个converters的引用了(这里也证实了java是值传递,不是引用传递).

因而再次改变那个lambda表达式为普通的加强for循环:

@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    /*converters = converters.stream().
            filter((converter)-> !(converter instanceof MappingJackson2HttpMessageConverter))
            .collect(Collectors.toList());*/
    for (HttpMessageConverter<?> converter : converters) {
        if (converter instanceof MappingJackson2HttpMessageConverter){
            converters.remove(converter);
        }
    }
    FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();
    //自定义配置...
    FastJsonConfig config = new FastJsonConfig();
    config.setSerializerFeatures(SerializerFeature.QuoteFieldNames,
            SerializerFeature.WriteEnumUsingToString,
            /*SerializerFeature.WriteMapNullValue,*/
            SerializerFeature.WriteDateUseDateFormat,
            SerializerFeature.DisableCircularReferenceDetect);
    fastJsonHttpMessageConverter.setFastJsonConfig(config);
    converters.add(fastJsonHttpMessageConverter);
}

再次运行,wtf?报错了:ConcurrentModificationException,原来使用for循环遍历过程当中不能进行remove操做,因而换成Iterator:

@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    /*converters = converters.stream()
            .filter((converter)-> !(converter instanceof MappingJackson2HttpMessageConverter))
            .collect(Collectors.toList());
    for (HttpMessageConverter<?> converter : converters) {
        if (converter instanceof MappingJackson2HttpMessageConverter){
            converters.remove(converter);
        }
    }*/
    Iterator<HttpMessageConverter<?>> iterator = converters.iterator();
    while(iterator.hasNext()){
        HttpMessageConverter<?> converter = iterator.next();
        if(converter instanceof MappingJackson2HttpMessageConverter){
            iterator.remove();
        }
    }
    FastJsonHttpMessageConverter fastJsonHttpMessageConverter = new FastJsonHttpMessageConverter();
    //自定义配置...
    FastJsonConfig config = new FastJsonConfig();
    config.setSerializerFeatures(SerializerFeature.QuoteFieldNames,
            SerializerFeature.WriteEnumUsingToString,
            /*SerializerFeature.WriteMapNullValue,*/
            SerializerFeature.WriteDateUseDateFormat,
            SerializerFeature.DisableCircularReferenceDetect);
    fastJsonHttpMessageConverter.setFastJsonConfig(config);
    converters.add(fastJsonHttpMessageConverter);
}

再次运行,我去,终于解决了,先是删除MappingJackson2HttpMessageConverter,而后添加FastJsonHttpMessageConverter,可是不是到为何进过一系列操做后,MappingJackson2HttpMessageConverter仍是添加进去了,可是因为FastJsonHttpMessageConverter在MappingJackson2HttpMessageConverter以前添加,因此对结果不影响.至此,解决了这个问题.

总结

1. 最重要的仍是解决了springboot2.0.2配置fastjson不生效的问题
2. 更加明白stream api返回的都是全新的对象
3. 更理解java是值传递而不是引用传递
4. 了解到想要在迭代过程当中对集合进行操做要用Iterator,而不是直接简单的for循环或者加强for循环

若有不正确的地方还请指出,谢谢.