fastJson和Jackson对比

今天在写spring boot时，发现spring默认带的转json包为jackson，而一般都大家都会引入fastjson来替换。
引入fastjson的方式为，首先引入alibaba的fastjson包，然后在启动类中继承WebMvcConfigurerAdapter 重写 configureMessageConverters

@Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
        super.configureMessageConverters(converters);
        //1定义转换器 converter
        FastJsonHttpMessageConverter converter = new FastJsonHttpMessageConverter();
        //配置fastjson
        FastJsonConfig config = new FastJsonConfig();
        config.setSerializerFeatures(SerializerFeature.PrettyFormat);
        //将fastjson 传入转换器
        converter.setFastJsonConfig(config);
        //将converter添加到converters当中
        converters.add(converter);
    }

为什么spring这么成熟的框架用的jackson而我们却要改变为fastjson呢，难道fastjson真的就很fast？
我做了一个测试

 //Spring 中默认用到的是Jackson   在框架搭建的时候一般都改用fastJson
     public static void main(String [] str) {
         Map map = new HashMap<String,Object>();
         map = getMapData(map,1000000);
        long fastJsonBegin =  System.currentTimeMillis();
         JSONObject fastJson = new JSONObject();
        //fastJson
         System.out.println("fastJson-------------------------------------------------");
        // System.out.println("fastJson"+fastJson.toJSONString(map));
         fastJson.toJSONString(map);
         long fastJsonEnd =  System.currentTimeMillis();
         System.out.println("fastJson-------------time------------------------------------"+(fastJsonEnd-fastJsonBegin));
         //jackson
         long jacksonBegin =  System.currentTimeMillis();
         ObjectMapper jackson = new ObjectMapper();
         try {
             System.out.println("jackson-------------------------------------------------");
             //System.out.println("jackson"+jackson.writeValueAsString(map));
             jackson.writeValueAsString(map);
             long jacksonEnd =  System.currentTimeMillis();
             System.out.println("jackson-------------time------------------------------------"+(jacksonEnd-jacksonBegin));
         } catch (JsonProcessingException e) {
             e.printStackTrace();
         }
     }

     public static Map getMapData(Map map,int count) {
        for (int i = 0;i < count;i++) {
            map.put("a"+i,i);
        }
        return map;
     }

得到的运行结果

fastJson-------------------------------------------------
fastJson-------------time------------------------------------445
jackson-------------------------------------------------
jackson-------------time------------------------------------1123

果然是fastjson以快一倍的速度碾压，于是我对上面的代码进行了改动，将获取时间放在了创建fastjson及jackson的后面

//Spring 中默认用到的是Jackson   在框架搭建的时候一般都改用fastJson
     public static void main(String [] str) {
         Map map = new HashMap<String,Object>();
         map = getMapData(map,1000000);
         JSONObject fastJson = new JSONObject();
        long fastJsonBegin =  System.currentTimeMillis();

        //fastJson
         System.out.println("fastJson-------------------------------------------------");
        // System.out.println("fastJson"+fastJson.toJSONString(map));
         fastJson.toJSONString(map);
         long fastJsonEnd =  System.currentTimeMillis();
         System.out.println("fastJson-------------time------------------------------------"+(fastJsonEnd-fastJsonBegin));
         //jackson
         ObjectMapper jackson = new ObjectMapper();
         long jacksonBegin =  System.currentTimeMillis();

         try {
             System.out.println("jackson-------------------------------------------------");
             //System.out.println("jackson"+jackson.writeValueAsString(map));
             jackson.writeValueAsString(map);
             long jacksonEnd =  System.currentTimeMillis();
             System.out.println("jackson-------------time------------------------------------"+(jacksonEnd-jacksonBegin));
         } catch (JsonProcessingException e) {
             e.printStackTrace();
         }
     }

结果为

fastJson-------------------------------------------------
fastJson-------------time------------------------------------385
jackson-------------------------------------------------
jackson-------------time------------------------------------309

很明显jackson的速度优于fastjson，只是，在创建对象时fastjson比jactson快
我们看一下两个的构造方法
fastjson

private static final long         serialVersionUID         = 1L;
    private static final int          DEFAULT_INITIAL_CAPACITY = 16;

    private final Map<String, Object> map;

    public JSONObject(){
        this(DEFAULT_INITIAL_CAPACITY, false);
    }
    public JSONObject(int initialCapacity, boolean ordered){
        if (ordered) {
            map = new LinkedHashMap<String, Object>(initialCapacity);
        } else {
            map = new HashMap<String, Object>(initialCapacity);
        }
    }

jackson

public ObjectMapper() {
        this(null, null, null);
    }

 public ObjectMapper(JsonFactory jf,
            DefaultSerializerProvider sp, DefaultDeserializationContext dc)
    {
        /* 02-Mar-2009, tatu: Important: we MUST default to using
         *   the mapping factory, otherwise tree serialization will
         *   have problems with POJONodes.
         * 03-Jan-2010, tatu: and obviously we also must pass 'this',
         *    to create actual linking.
         */
        if (jf == null) {
            _jsonFactory = new MappingJsonFactory(this);
        } else {
            _jsonFactory = jf;
            if (jf.getCodec() == null) { // as per [JACKSON-741]
                _jsonFactory.setCodec(this);
            }
        }
        _subtypeResolver = new StdSubtypeResolver();
        RootNameLookup rootNames = new RootNameLookup();
        // and default type factory is shared one
        _typeFactory = TypeFactory.defaultInstance();

        SimpleMixInResolver mixins = new SimpleMixInResolver(null);
        _mixIns = mixins;
        BaseSettings base = DEFAULT_BASE.withClassIntrospector(defaultClassIntrospector());
        _configOverrides = new ConfigOverrides();
        _serializationConfig = new SerializationConfig(base,
                    _subtypeResolver, mixins, rootNames, _configOverrides);
        _deserializationConfig = new DeserializationConfig(base,
                    _subtypeResolver, mixins, rootNames, _configOverrides);

        // Some overrides we may need
        final boolean needOrder = _jsonFactory.requiresPropertyOrdering();
        if (needOrder ^ _serializationConfig.isEnabled(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY)) {
            configure(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY, needOrder);
        }
        
        _serializerProvider = (sp == null) ? new DefaultSerializerProvider.Impl() : sp;
        _deserializationContext = (dc == null) ?
                new DefaultDeserializationContext.Impl(BeanDeserializerFactory.instance) : dc;

        // Default serializer factory is stateless, can just assign
        _serializerFactory = BeanSerializerFactory.instance;
    }

这样就一目了然的看到了耗时的原因