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()); 
    } 
  } 
}

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。

"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"));
// 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"));
// 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。