FastJSON 简介及其Map/JSON/String 互转

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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 = 64;   private short vshort = 128;   private int vint = 65535;   private long vlong = 9999999L;   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 = {1, 2, 3, 4};   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":174398800,     "barDate":1322062233062,     "barName":"sss_0.62378174"   },{     "barAge":38938962,     "barDate":1322062233062,     "barName":"sss_0.36014742"   }],   "avString":["aaa","bbb","ccc"],   "avboolean":[true,false,true,true],   "avint":[1,2,3,4],   "bar":{     "barAge":1601495948,     "barDate":1322062233062,     "barName":"sss_0.46644872"   },   "dddd":1322062233046,   "listBar":[     {       "barAge":-1090113522,       "barDate":1322062233062,       "barName":"sss_0.83562374"     },     {       "barAge":478603194,       "barDate":1322062233062,       "barName":"sss_0.59483266"     },     {       "barAge":1118357669,       "barDate":1322062233062,       "barName":"sss_0.9961642"     }   ],   "listString":[     "listString1",     "listString2",     "listString3"   ],   "map":{"x":"s11111x","y":"s22222y","z":"s33333z"},   "v_Date":1322062233046,   "vboolean":false,   "vbyte":64,   "vchar":"x",   "vdouble":22.203,   "vfloat":12.1,   "vint":65535,   "vlong":9999999,   "vshort":128 } {"avBar":[{"barAge":174398800,"barDate":"2011-11-23 23:30:33","barName":"sss_0.62378174"},{"barAge":38938962,"barDate":"2011-11-23 23:30:33","barName":"sss_0.36014742"}],"avString":["aaa","bbb","ccc"],"avboolean":[true,false,true,true],"avint":[1,2,3,4],"bar":{"barAge":1601495948,"barDate":"2011-11-23 23:30:33","barName":"sss_0.46644872"},"dddd":"2011-11-23 23:30:33","listBar":[{"barAge":-1090113522,"barDate":"2011-11-23 23:30:33","barName":"sss_0.83562374"},{"barAge":478603194,"barDate":"2011-11-23 23:30:33","barName":"sss_0.59483266"},{"barAge":1118357669,"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":64,"vchar":"x","vdouble":22.203,"vfloat":12.1,"vint":65535,"vlong":9999999,"vshort":128} Process finished with exit code 0

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"));// 11String o = "{'area':{'area':'1','pagetype':'home'},'pagetype':'home'}";System.out.println(((Map) JSONObject.parseObject(o).get("area")).get("area"));// 1String 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"));// nullSystem.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。

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