FastJSON 简介及其Map/JSON/String 互转

在日志解析，前后端数据传输交互中，经常会遇到 String 与 map、json、xml 等格式相互转换与解析的场景，其中 json 基本成为了跨语言、跨前后端的事实上的标准数据交互格式。应该来说各个语言中解析 json 的库都一大片（具体 json 格式与三方库的介绍请见： http://www.json.org/json-zh.html），比如 python 都集成在了内置库中，成为标准 API，今天我们要聊的是 java 中如何方便的使用 json 格式。

从上面的链接介绍中我们可以看到，java 的三方 json 库是最多的，可谓百花齐放百家争鸣的节奏。。。但是，某些库存在链式依赖的问题，使用的时候要注意，如果你没用 maven 管你你的依赖，用起来会很痛苦，比如 json-lib、smart-json 等。下面我要推荐的是阿里巴巴工程师开源的一个 json 库：FastJSON，这个库在解析速度和易用性上来说都很不错。

1、了解fastjson

1.1 Fastjson介绍

Fastjson是一个Java语言编写的JSON处理器。
1、遵循 http://json.org标准，为其官方网站收录的参考实现之一。
2、功能qiang打，支持JDK的各种类型，包括基本的JavaBean、Collection、Map、Date、Enum、泛型。
3、无依赖，不需要例外额外的jar，能够直接跑在JDK上。
4、开源，使用Apache License 2.0协议开源。

1.2 如果获得Fastjson？
https://github.com/alibaba/fastjson

2、主要的使用入口

Fastjson API入口类是com.alibaba.fastjson.JSON，常用的序列化操作都可以在JSON类上的静态方法直接完成。

public static final Object parse(String text); // 把JSON文本parse为JSONObject或者JSONArray  public static final JSONObject parseObject(String text)； // 把JSON文本parse成JSONObject     public static final <T> T parseObject(String text, Class<T> clazz); // 把JSON文本parse为JavaBean  public static final JSONArray parseArray(String text); // 把JSON文本parse成JSONArray  public static final <T> List<T> parseArray(String text, Class<T> clazz); //把JSON文本parse成JavaBean集合  public static final String toJSONString(Object object); // 将JavaBean序列化为JSON文本  public static final String toJSONString(Object object, boolean prettyFormat); // 将JavaBean序列化为带格式的JSON文本  public static final Object toJSON(Object javaObject); 将JavaBean转换为JSONObject或者JSONArray。

3、有关类库的一些说明

SerializeWriter：相当于StringBuffer

JSONArray：相当于List<Object>

JSONObject：相当于Map<String, Object>

JSON反序列化没有真正数组，本质类型都是List<Object>

4、fastjson还有很多很高级的特性

比如支持注解、支持全类型序列化，这些都是很好的特性，功能强大，不在本次测试范围。

5、测试代码

package lavasoft.stu.json;   import com.alibaba.fastjson.JSON;  import com.alibaba.fastjson.serializer.SerializeConfig;  import com.alibaba.fastjson.serializer.SimpleDateFormatSerializer;   import java.util.*;   /**  * Created by IntelliJ IDEA.  *  * @author leizhimin 11-11-22 上午9:15  */  public class Foo {   private String vString = "vStringhehhehe";   private char vchar = 'x';    private byte vbyte = ;   private short vshort = ;   private int vint = ;   private long vlong = L;    private float vfloat = 12.1f;   private double vdouble = 22.203d;    private boolean vboolean = false;   //	private Date vdate = new Date();   private Date dddd = new Date();   private Date vDate = new Date();   private Date v_Date = new Date();   private Object vnull = null;    private String[] avString = {"aaa", "bbb", "ccc"};   private int[] avint = {, , , };   private boolean[] avboolean = {true, false, true, true};    private List<String> listString = new ArrayList<String>();   private Map<String, String> map = new HashMap<String, String>();    private Bar bar = new Bar();   private Bar[] avBar = {new Bar(), new Bar()};   private List<Bar> listBar = new ArrayList<Bar>();    {    listString.add("listString1");    listString.add("listString2");    listString.add("listString3");     map.put("x", "s11111x");    map.put("y", "s22222y");    map.put("z", "s33333z");     listBar.add(new Bar());    listBar.add(new Bar());    listBar.add(new Bar());   }      public String getvString() {    return vString;   }    public void setvString(String vString) {    this.vString = vString;   }    public char getVchar() {    return vchar;   }    public void setVchar(char vchar) {    this.vchar = vchar;   }    public byte getVbyte() {    return vbyte;   }    public void setVbyte(byte vbyte) {    this.vbyte = vbyte;   }    public short getVshort() {    return vshort;   }    public void setVshort(short vshort) {    this.vshort = vshort;   }    public int getVint() {    return vint;   }    public void setVint(int vint) {    this.vint = vint;   }    public long getVlong() {    return vlong;   }    public void setVlong(long vlong) {    this.vlong = vlong;   }    public float getVfloat() {    return vfloat;   }    public void setVfloat(float vfloat) {    this.vfloat = vfloat;   }    public double getVdouble() {    return vdouble;   }    public void setVdouble(double vdouble) {    this.vdouble = vdouble;   }    public boolean isVboolean() {    return vboolean;   }    public void setVboolean(boolean vboolean) {    this.vboolean = vboolean;   }    public Date getDddd() {    return dddd;   }    public void setDddd(Date dddd) {    this.dddd = dddd;   }    public Date getV_Date() {    return v_Date;   }    public void setV_Date(Date v_Date) {    this.v_Date = v_Date;   }    public Date getvDate() {    return vDate;   }    public void setvDate(Date vDate) {    this.vDate = vDate;   }    public Object getVnull() {    return vnull;   }    public void setVnull(Object vnull) {    this.vnull = vnull;   }    public String[] getAvString() {    return avString;   }    public void setAvString(String[] avString) {    this.avString = avString;   }    public int[] getAvint() {    return avint;   }    public void setAvint(int[] avint) {    this.avint = avint;   }    public boolean[] getAvboolean() {    return avboolean;   }    public void setAvboolean(boolean[] avboolean) {    this.avboolean = avboolean;   }    public List<String> getListString() {    return listString;   }    public void setListString(List<String> listString) {    this.listString = listString;   }    public Map<String, String> getMap() {    return map;   }    public void setMap(Map<String, String> map) {    this.map = map;   }    public Bar getBar() {    return bar;   }    public void setBar(Bar bar) {    this.bar = bar;   }    public Bar[] getAvBar() {    return avBar;   }    public void setAvBar(Bar[] avBar) {    this.avBar = avBar;   }    public List<Bar> getListBar() {    return listBar;   }    public void setListBar(List<Bar> listBar) {    this.listBar = listBar;   }  }

package lavasoft.stu.json;   import com.alibaba.fastjson.JSON;  import com.alibaba.fastjson.serializer.SerializeConfig;  import com.alibaba.fastjson.serializer.SimpleDateFormatSerializer;   import java.util.Date;  import java.util.Random;   /**  * Created by IntelliJ IDEA.  *  * @author leizhimin 11-11-22 上午9:15  */  public class Bar {   public static SerializeConfig mapping = new SerializeConfig();   private String barName;   private int barAge;   private Date barDate = new Date();   static {    mapping.put(Date.class, new SimpleDateFormatSerializer("yyyy-MM-dd"));   }   {    Random r = new Random();    barName = "sss_"+String.valueOf(r.nextFloat());    barAge = r.nextInt();   }    public static void main(String[] args) {    Object obj = JSON.toJSON(new Bar());    String x1 = JSON.toJSONString(new Bar(), true);    System.out.println(x1);    String x2 = JSON.toJSONString(new Bar(), mapping);    System.out.println(x2);   }    public String getBarName() {    return barName;   }    public void setBarName(String barName) {    this.barName = barName;   }    public int getBarAge() {    return barAge;   }    public void setBarAge(int barAge) {    this.barAge = barAge;   }    public Date getBarDate() {    return barDate;   }    public void setBarDate(Date barDate) {    this.barDate = barDate;   }    @Override   public String toString() {    return "Bar{" +      "barName='" + barName + '\'' +      ", barAge=" + barAge +      ", barDate=" + barDate +      '}';   }  }

package lavasoft.stu.json;   import com.alibaba.fastjson.JSON;  import com.alibaba.fastjson.JSONArray;  import com.alibaba.fastjson.serializer.SerializeConfig;  import com.alibaba.fastjson.serializer.SimpleDateFormatSerializer;   import java.util.*;   /**  * Created by 2IntelliJ IDEA.  *  * @author leizhimin 11-11-22 上午9:45  */  public class Test {   private static SerializeConfig mapping = new SerializeConfig(); static {    mapping.put(Date.class, new SimpleDateFormatSerializer("yyyy-MM-dd HH:mm:ss"));   }    public static void main(String[] args) {    Foo f1 = new Foo();    Date date = new Date();    String text = JSON.toJSONString(date, mapping);    System.out.println(text);    System.out.println(JSON.toJSONString(f1, true));    String x2 =JSON.toJSONString(f1, mapping);    System.out.println(x2);   }    public static void json2List(){    //List -> JSON array    List<Bar> barList = new ArrayList<Bar>();    barList.add(new Bar());    barList.add(new Bar());    barList.add(new Bar());    String json= JSON.toJSONString(barList, true);    System.out.println(json);    //JSON array -> List    List<Bar> barList1 = JSON.parseArray(json,Bar.class);    for (Bar bar : barList1) {     System.out.println(bar.toString());    }   }    public static void json2Map(){    //Map -> JSON    Map<String,Bar> map = new HashMap<String, Bar>();    map.put("a",new Bar());    map.put("b",new Bar());    map.put("c",new Bar());    String json = JSON.toJSONString(map,true);    System.out.println(json);    //JSON -> Map    Map<String,Bar> map1 = (Map<String,Bar>)JSON.parse(json);    for (String key : map1.keySet()) {     System.out.println(key+":"+map1.get(key));    }   }    public static void array2JSON(){    String[] arr_String    = {"a","b","c"};    String json_arr_String = JSON.toJSONString(arr_String,true);    System.out.println(json_arr_String);    JSONArray jsonArray = JSON.parseArray(json_arr_String);    for (Object o : jsonArray) {     System.out.println(o);    }    System.out.println(jsonArray);   }   public static void array2JSON2(){    Bar[] arr_Bar    = {new Bar(),new Bar(),new Bar()};    String json_arr_Bar = JSON.toJSONString(arr_Bar,true);    System.out.println(json_arr_Bar);    JSONArray jsonArray = JSON.parseArray(json_arr_Bar);    for (Object o : jsonArray) {     System.out.println(o);    }    System.out.println(jsonArray);   }    public static void map2JSON(){    Map map = new HashMap();    map.put("a","aaa");    map.put("b","bbb");    map.put("c","ccc");    String json=JSON.toJSONString(map);    System.out.println(json);    Map map1 = JSON.parseObject(json);    for (Object o : map.entrySet()) {     Map.Entry<String,String> entry = (Map.Entry<String,String>)o;     System.out.println(entry.getKey()+"--->"+entry.getValue());    }   }  }

说明：

SerializeConfig：是对序列化过程中一些序列化过程的特殊配置，这里用作日期格式的定义。

有关需要带类型的全类型序列化过程，需要调用JSON.toJSONStringZ()方法。

需要美化输出时候，需要打开序列化美化开关，在方法中true那个参数。

输出结果：

"2011-11-23 23:30:33"  {    "avBar":[{      "barAge":,      "barDate":,      "barName":"sss_0.62378174"    },{      "barAge":,      "barDate":,      "barName":"sss_0.36014742"    }],    "avString":["aaa","bbb","ccc"],    "avboolean":[true,false,true,true],    "avint":[,,,],    "bar":{      "barAge":,      "barDate":,      "barName":"sss_0.46644872"    },    "dddd":,    "listBar":[      {        "barAge":-,        "barDate":,        "barName":"sss_0.83562374"      },      {        "barAge":,        "barDate":,        "barName":"sss_0.59483266"      },      {        "barAge":,        "barDate":,        "barName":"sss_0.9961642"      }    ],    "listString":[      "listString1",      "listString2",      "listString3"    ],    "map":{"x":"s11111x","y":"s22222y","z":"s33333z"},    "v_Date":,    "vboolean":false,    "vbyte":,    "vchar":"x",    "vdouble":22.203,    "vfloat":12.1,    "vint":,    "vlong":,    "vshort":  }  {"avBar":[{"barAge":,"barDate":"2011-11-23 23:30:33","barName":"sss_0.62378174"},{"barAge":,"barDate":"2011-11-23 23:30:33","barName":"sss_0.36014742"}],"avString":["aaa","bbb","ccc"],"avboolean":[true,false,true,true],"avint":[,,,],"bar":{"barAge":,"barDate":"2011-11-23 23:30:33","barName":"sss_0.46644872"},"dddd":"2011-11-23 23:30:33","listBar":[{"barAge":-,"barDate":"2011-11-23 23:30:33","barName":"sss_0.83562374"},{"barAge":,"barDate":"2011-11-23 23:30:33","barName":"sss_0.59483266"},{"barAge":,"barDate":"2011-11-23 23:30:33","barName":"sss_0.9961642"}],"listString":["listString1","listString2","listString3"],"map":{"x":"s11111x","y":"s22222y","z":"s33333z"},"v_Date":"2011-11-23 23:30:33","vboolean":false,"vbyte":,"vchar":"x","vdouble":22.203,"vfloat":12.1,"vint":,"vlong":,"vshort":}   Process finished with exit code

测试小例子：

JSONObject json = new JSONObject(); json.put("aa", "11"); json.put("bb", "22"); json.put("cc", "33"); String jsonStr = json.toString(); System.out.println(jsonStr); // {"aa":"11","bb":"22","cc":"33"}	   System.out.println(JSONObject.parseObject(jsonStr).get("aa")); // 11  String o = "{'area':{'area':'1','pagetype':'home'},'pagetype':'home'}"; System.out.println(((Map) JSONObject.parseObject(o).get("area")).get("area")); // 1 String text = JSON.toJSONString(o); Map<String, Object> userMap =    JSON.parseObject(o, new TypeReference<Map<String, Object>>() {}); System.out.println(((Map) userMap.get("area")).get("NotExsit")); // null  System.out.println(JSON.toJSONString((Map) userMap.get("area"))); // {"area":"1","pagetype":"home"}

fastjson通过各方面测试都很好，功能性能都是No.1，喜欢，它的源代码质量很高，作者也煞费苦心，将性能做到了最好，全免超越其他的json类库。

从其中的源代码中，可以学到很多东西，在阅读源码后，不得不佩服作者高超的程序设计水平，和高质量的编码。

6、Refer：

6.1 FastJSON应用前测试

http://lavasoft.blog.51cto.com/62575/723192

6.2 alibaba fastjson(json序列化器)序列化部分源码解析-1-总体分析

http://www.iflym.com/index.php/code/alibaba-fastjson-json-serializer-chapter-source-analyse-one-global-analyse.html

6.3 FastJson---高性能JSON开发包

http://blog.csdn.net/glarystar/article/details/6654494