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fastjson1.1 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/fastjson2、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JSONArraypublic 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JavaBeanpublic static final JSONArray parseArray(String text); // 把JSON文本parse成JSONArraypublic 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StringBufferjsonArray：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,"barName":"sss_0.36014742" }],"avString":["aaa","ccc"],"avboolean":[true,true],"avint":[1,4],"bar":{ "barage":1601495948,"barName":"sss_0.46644872" },"dddd":1322062233046,"listBar":[ { "barage":-1090113522,"barName":"sss_0.83562374" },{ "barage":478603194,"barName":"sss_0.59483266" },{ "barage":1118357669,"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,"barName":"sss_0.36014742"}],"bar":{"barage":1601495948,"barName":"sss_0.46644872"},"dddd":"2011-11-23 23:30:33","listBar":[{"barage":-1090113522,"barName":"sss_0.83562374"},{"barage":478603194,"barName":"sss_0.59483266"},{"barage":1118357669,"barName":"sss_0.9961642"}],"listString":["listString1","listString3"],"v_Date":"2011-11-23 23:30:33","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。
