FastJSON 原理剖析 以及 和 Jackson的对比 who is the most fast!

FastJSON定义： FastJSON是一个阿里巴巴内部人员开发的，用于JSON对象和普通类对象互相转换的库。号称性能超越Jackson，今天我们就来看看，阿里巴巴大牛 vs Tatu Saloranta，到底 who is the most awesome!

FastJSON原理： 

-对象 to JSON ：利用反射找到对象类的所有Get方法，然后把"get"去掉，小写化，作为JSON的每个key值，如 getA  对应的key值为 a，而与真实的类成员名无关。

-JSON to  pojo ：先同样通过反射找到对象类所有的Set方法，然后使用无参数构造函数（所以一定要有无参数的构造函数）新建一个类对象，从JSON字符串中取出一个key 如 a，先大写化为A，那么从所有Set方法中找到 SetA()，然后进行赋值。 如果找不到 setA （seta也不行），那么该值被忽略，也不报错。

Jackson 的原理和FastJson一致，但是在 JSON to Java pojo的步骤中，做了更加科学的check，因而能识别seta这样的小写。但是如果getA 和geta都找不到，则会抛出异常（除非把a设置为忽略）。

其他的步骤原理和FastJSON类似。

测试验证代码：

package jar;import com.alibaba.fastjson.JSON;public class Test{private int aaa=0;private String bbb = "000";public Test() {// TODO Auto-generated constructor stubaaa = 1;bbb = "111";System.out.println(" default construct function is called!!!");}public Test(int a ,String b) {// TODO Auto-generated constructor stubaaa = a;bbb = b;System.out.println("construct 2 function is called!!!");}public int getA() {return aaa;}public void seta(int a){this.aaa =a;}public String getB() {return bbb;} //test public static void main(String[] args) throws Exception   {          Test test =new Test(2,"222");   String code =  JSON.toJSONString(test);   System.out.println(code);   Test reverse = JSON.parseObject(code,Test.class);   System.out.println(reverse.getA());   System.out.println(reverse.getB()); }}

下面是对 FastJson 和 Jackson  （pojo to json-编码） 以及 （json to pojo-解码）以及综合（编码+解码） 在不同成员数量 下 ，不同循环次数的耗时（ns纳秒）对比。

//         code + decode -----------------------------------------------------//         10000  - 23 members//   Jackson :235750737 ns//   FastJSON:347795550 ns//         10000  - 2 members//   Jackson :164173126 ns//   FastJSON:159078284 ns      //       100000 - 23 members//   Jackson :1004902734 ns//   FastJSON:1689072614 ns//       100000 - 2 members //   Jackson :392344461 ns//   FastJSON:299521240 ns   //        1000000 - 23 members//   Jackson :8547741285 ns//   FastJSON:15377369425 ns//        1000000 - 2 members//   Jackson :2581267623 ns//   FastJSON:1591827729 ns   //         code only -------------------------------------------------------//         10000  - 23 members//   Jackson :115036100 ns//   FastJSON:158681243 ns//         10000  - 2 members//   Jackson :87886170 ns//   FastJSON:103086025 ns      //       100000 - 23 members//   Jackson :417539325 ns//   FastJSON:349358062 ns//       100000 - 2 members //   Jackson :185865488 ns//   FastJSON:144893485 ns   //        1000000 - 23 members//   Jackson :3384171740 ns//   FastJSON:2200190119 ns//        1000000 - 2 members//   Jackson :1193815955 ns//   FastJSON:568776506 ns      //         decode only -------------------------------------------------------//         10000  - 23 members//   Jackson :122597862 ns//   FastJSON:183567261 ns//         10000  - 2 members//   Jackson :75418145 ns//   FastJSON:47832689 ns      //       100000 - 23 members//   Jackson :497670344 ns//   FastJSON:1254994458 ns//       100000 - 2 members //   Jackson :165368101 ns//   FastJSON:117555618 ns   //        1000000 - 23 members//   Jackson :4189147981 ns//   FastJSON:12004873228 ns//        1000000 - 2 members//   Jackson :999578584 ns//   FastJSON:863444723 ns

结论：

编码(pojo to json):  当循环数量较小时，FastJSON的性能 低于 JackSON；

    当循环数量越大时，FastJSON的性能开始超过Jackson；

解码( json to pojo):当成员数量越大时，FastJSON的相对性能越差，JackSON的相对性能则越好； 

   当成员数量越小时，FastJSON的性能越好。

综合(编码+解码): 当成员变量数量越大时，Jackson 获胜。无关于循环数量。 

当成员变量数量越小时，FastJSON获胜。

一般情况下，系统中的循环数量一般不会大的惊人，应该是偏小的。而成员变量变多，是一个企业级系统常见的情况。

SO， who is the most fast or best? 我就不点出了。

。。。

Whatever， 两个JSON框架都是很棒的。而且本人很喜欢FastJSON的易用性，干净。 

有时间，有兴趣的可以继续研究研究FastJSON在多成员变量解码时的劣势是什么原因导致的。

付上测试代码：

package jar;import java.io.StringWriter;import org.codehaus.jackson.JsonEncoding;import org.codehaus.jackson.JsonGenerator;import org.codehaus.jackson.map.ObjectMapper;import com.alibaba.fastjson.JSON;public class Test{private int aaa=0;private String bbb = "000";private String c1 = "000";private String c2 = "000";private String c3 = "000";private String c4 = "000";private String c5 = "000";private String c6 = "000";private String c7 = "000";private String c8 = "000";private String c9 = "000";private String c10 = "000";private String c11 = "000";private String c12 = "000";private String c13 = "000";private String c14 = "000";private String c15 = "000";private String c16 = "000";private String c17 = "000";private String c18 = "000";private String c19 = "000";private String c20 = "000";private String c21 = "000";public Test(){}public Test(int a ,String b) {// TODO Auto-generated constructor stubaaa = a;bbb = b;//System.out.println("construct 2 function is called!!!");}public int getA() {return aaa;}public void setA(int a){this.aaa = a;}public String getB() {return bbb;}public void setB(String b) {this.bbb = b;}public String getC1() {return c1;}public void setC1(String c1) {this.c1 = c1;}public String getC2() {return c2;}public void setC2(String c2) {this.c2 = c2;}public String getC3() {return c3;}public void setC3(String c3) {this.c3 = c3;}public String getC4() {return c4;}public void setC4(String c4) {this.c4 = c4;}public String getC5() {return c5;}public void setC5(String c5) {this.c5 = c5;}public String getC6() {return c6;}public void setC6(String c6) {this.c6 = c6;}public String getC7() {return c7;}public void setC7(String c7) {this.c7 = c7;}public String getC8() {return c8;}public void setC8(String c8) {this.c8 = c8;}public String getC9() {return c9;}public void setC9(String c9) {this.c9 = c9;}public String getC10() {return c10;}public void setC10(String c10) {this.c10 = c10;}public String getC11() {return c11;}public void setC11(String c11) {this.c11 = c11;}public String getC12() {return c12;}public void setC12(String c12) {this.c12 = c12;}public String getC13() {return c13;}public void setC13(String c13) {this.c13 = c13;}public String getC14() {return c14;}public void setC14(String c14) {this.c14 = c14;}public String getC15() {return c15;}public void setC15(String c15) {this.c15 = c15;}public String getC16() {return c16;}public void setC16(String c16) {this.c16 = c16;}public String getC17() {return c17;}public void setC17(String c17) {this.c17 = c17;}public String getC18() {return c18;}public void setC18(String c18) {this.c18 = c18;}public String getC19() {return c19;}public void setC19(String c19) {this.c19 = c19;}public String getC20() {return c20;}public void setC20(String c20) {this.c20 = c20;}public String getC21() {return c21;}public void setC21(String c21) {this.c21 = c21;}//test /** * @param args * @throws Exception */public static void main(String[] args) throws Exception   {            Test test =new Test(2,"222");         //JackJSON 初始化   ObjectMapper objectMapper = new ObjectMapper();      long startTime=0;   //获取开始时间   long endTime=0; //获取结束时间      int  loopCount  =100000;   //         code + decode -----------------------------------------------------//         10000  - 23 members//   Jackson :235750737 ns//   FastJSON:347795550 ns//         10000  - 2 members//   Jackson :164173126 ns//   FastJSON:159078284 ns      //       100000 - 23 members//   Jackson :1004902734 ns//   FastJSON:1689072614 ns//       100000 - 2 members //   Jackson :392344461 ns//   FastJSON:299521240 ns   //        1000000 - 23 members//   Jackson :8547741285 ns//   FastJSON:15377369425 ns//        1000000 - 2 members//   Jackson :2581267623 ns//   FastJSON:1591827729 ns   //         code only -------------------------------------------------------//         10000  - 23 members//   Jackson :115036100 ns//   FastJSON:158681243 ns//         10000  - 2 members//   Jackson :87886170 ns//   FastJSON:103086025 ns      //       100000 - 23 members//   Jackson :417539325 ns//   FastJSON:349358062 ns//       100000 - 2 members //   Jackson :185865488 ns//   FastJSON:144893485 ns   //        1000000 - 23 members//   Jackson :3384171740 ns//   FastJSON:2200190119 ns//        1000000 - 2 members//   Jackson :1193815955 ns//   FastJSON:568776506 ns      //         decode only -------------------------------------------------------//         10000  - 23 members//   Jackson :122597862 ns//   FastJSON:183567261 ns//         10000  - 2 members//   Jackson :75418145 ns//   FastJSON:47832689 ns      //       100000 - 23 members//   Jackson :497670344 ns//   FastJSON:1254994458 ns//       100000 - 2 members //   Jackson :165368101 ns//   FastJSON:117555618 ns   //        1000000 - 23 members//   Jackson :4189147981 ns//   FastJSON:12004873228 ns//        1000000 - 2 members//   Jackson :999578584 ns//   FastJSON:863444723 ns      //Jackson       startTime =  System.nanoTime();    for(int i=0;i<loopCount;i++)   {   StringWriter sw = new StringWriter();   JsonGenerator jsonGenerator = objectMapper.getJsonFactory().createJsonGenerator(sw);   jsonGenerator.writeObject(test);    String result = sw.toString();  // Test acc = objectMapper.readValue(result, Test.class);    }   endTime =  System.nanoTime();   System.out.println("Jackson :"+(endTime-startTime)+" ns");        startTime =  System.nanoTime();   //FastJSON   for(int i=0;i<loopCount;i++)   {   String code =  JSON.toJSONString(test); // Test reverse = JSON.parseObject(code,Test.class);   }   endTime =  System.nanoTime();   System.out.println("FastJSON:"+(endTime-startTime)+" ns"); }}

还有一篇TS回复挑战者的基准测试结果的文章，虽然和本文没有直接关系，但是反映了一些东西。可以了解了解。

http://www.infoq.com/cn/news/2014/05/jackson-founder-responds