今天来和大家一起学习一下开源JSON框架。以前听说过同事提起JsonObject是现有json库中提供运行效率最慢的一种，趁着今天有时间，了解了一下相对运行效率比较快的，由Google提供的Gson，Jackson，FastJson框架。
其中FastJson号称运行效率最快的且使用起来非常简单。下载地址：https://github.com/AlibabaTech/fastjson
以下举例几个最常用到转换：
pubic class UserInfo implements Serializable{
private String name;
private int age;
public void setName(String name){
this.name=name;
}
public String getName(){
return name;
}
public void setAge(int age){
this.age=age;
}
public int getAge(){
return age;
}
}
//将对象转换成json字符串
public class Test1{
public static void main(String[] args){
UserInfo info=new UserInfo();
info.setName("zhangsan");
info.setAge(24);
String str_json=JSON.toJSONString(info);
}
}
//将各集合转换成json字符串
public static void test2() {
HashSet<String, Object> map = new HashMap<String, Object>();
map.put("username", "zhangsan");
map.put("age", 24);
map.put("sex", "男");
//map集合
HashMap<String, Object> temp = new HashMap<String, Object>();
temp.put("name", "xiaohong");
temp.put("age", "23");
map.put("girlInfo", temp);
//list集合
List<String> list = new ArrayList<String>();
list.add("爬山");
list.add("骑车");
list.add("旅游");
map.put("hobby", list);
/*JSON 序列化，默认序列化出的JSON字符串中键值对是使用双引号，如果需要单引号的JSON字符串， [eg:String jsonString = JSON.toJSONString(map, SerializerFeature.UseSingleQuotes);]
*fastjson序列化时可以选择的SerializerFeature有十几个属性，你可以按照自己的需要去选择使用。
*/
String jsonString = JSON.toJSONString(map);
}
//将json字符串转换为对象
public void test3(){
String json="{\"name\":\"chenggang\",\"age\":24}";
UserInfo userInfo=JSON.parseObject(json,UserInfo.class);
}
//将json字符串转换为集合对象
public static void test4(){
String json="{\"user\":{\"name\":\"zhangsan\",\"age\":25}}";
Map<String, UserInfoBean> map = JSON.parseObject(json, new TypeReference<Map<String, UserInfoBean>>(){});
// List<UserInfoBean> list = JSON.parseObject(json, new TypeReference<ArrayList<UserInfoBean>>(){});
// HashSet<AdvanceHeaderInfo> set = JSON.parseObject(json, new TypeReference<HashSet<AdvanceHeaderInfo>>(){});
}
//json日期的转换
public void test5(){
Date date=new Date();
//输出毫秒值
System.out.println(JSON.toJSONString(date));
//默认格式为yyyy-MM-dd HH:mm:ss
System.out.println(JSON.toJSONString(date, SerializerFeature.WriteDateUseDateFormat));
//根据自定义格式输出日期
System.out.println(JSON.toJSONStringWithDateFormat(date, "yyyy-MM-dd", SerializerFeature.WriteDateUseDateFormat));
}之后是Jackson。Jackson也是运行效率中的佼佼者。下载地址：https://github.com/FasterXML/jackson
以下举例几个最常用到转换：
//初始化bean对象
public class JacksonTest {
private JsonGenerator jsonGenerator = null;
private ObjectMapper objectMapper = null;
private AccountBean bean = null;
@Before
public void init() {
bean = new AccountBean();
bean.setAddress("china-Guangzhou");
bean.setEmail("[email protected]");
bean.setId(1);
bean.setName("hoojo");
objectMapper = new ObjectMapper();
try {
jsonGenerator = objectMapper.getJsonFactory().createJsonGenerator(System.out, JsonEncoding.UTF8);
} catch (IOException e) {
e.printStackTrace();
}
}
@After
public void destory() {
try {
if (jsonGenerator != null) {
jsonGenerator.flush();
}
if (!jsonGenerator.isClosed()) {
jsonGenerator.close();
}
jsonGenerator = null;
objectMapper = null;
bean = null;
System.gc();
} catch (IOException e) {
e.printStackTrace();
}
}
}
//将对象转换成json字符串
public void writeEntityJSON() {
try {
System.out.println("jsonGenerator");
//writeObject可以转换java对象，eg:JavaBean/Map/List/Array等
jsonGenerator.writeObject(UserInfo);
//writeValue具有和writeObject相同的功能
objectMapper.writeValue(System.out, UserInfo);
} catch (IOException e) {
e.printStackTrace();
}
}
//将各集合转换成json字符串
public void writeMapJSON() {
try {
Map<String, Object> map = new HashMap<String, Object>();
map.put("name", bean.getName());
map.put("account", bean);
bean = new AccountBean();
bean.setAddress("china-Beijin");
bean.setEmail("[email protected]");
map.put("account2", bean);
System.out.println("jsonGenerator");
jsonGenerator.writeObject(map);
System.out.println("");
System.out.println("objectMapper");
objectMapper.writeValue(System.out, map);
} catch (IOException e) {
e.printStackTrace();
}
}
public void writeListJSON() {
try {
List<AccountBean> list = new ArrayList<AccountBean>();
list.add(bean);
bean = new AccountBean();
bean.setId(2);
bean.setAddress("address2");
bean.setEmail("email2");
bean.setName("haha2");
list.add(bean);
System.out.println("jsonGenerator");
//list转换成JSON字符串
jsonGenerator.writeObject(list);
System.out.println();
System.out.println("ObjectMapper");
//用objectMapper直接返回list转换成的JSON字符串
System.out.println("1###" + objectMapper.writeValueAsString(list));
System.out.print("2###");
//objectMapper list转换成JSON字符串
objectMapper.writeValue(System.out, list);
} catch (IOException e) {
e.printStackTrace();
}
}
//将json字符串转换为对象
public void readJson2Entity() {
String json = "{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}";
try {
AccountBean acc = objectMapper.readValue(json, AccountBean.class);
System.out.println(acc.getName());
System.out.println(acc);
} catch (JsonParseException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
//将json字符串转换为集合对象
public void readJson2List() {
String json = "[{\"address\": \"address2\",\"name\":\"haha2\",\"id\":2,\"email\":\"email2\"},"+
"{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}]";
try {
List<LinkedHashMap<String, Object>> list = objectMapper.readValue(json, List.class);
System.out.println(list.size());
for (int i = 0; i < list.size(); i++) {
Map<String, Object> map = list.get(i);
Set<String> set = map.keySet();
for (Iterator<String> it = set.iterator();it.hasNext();) {
String key = it.next();
System.out.println(key + ":" + map.get(key));
}
}
} catch (JsonParseException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public void readJson2Array() {
String json = "[{\"address\": \"address2\",\"name\":\"haha2\",\"id\":2,\"email\":\"email2\"},"+
"{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}]";
try {
AccountBean[] arr = objectMapper.readValue(json, AccountBean[].class);
System.out.println(arr.length);
for (int i = 0; i < arr.length; i++) {
System.out.println(arr[i]);
}
} catch (JsonParseException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
public void readJson2Map() {
String json = "{\"success\":true,\"A\":{\"address\": \"address2\",\"name\":\"haha2\",\"id\":2,\"email\":\"email2\"},"+
"\"B\":{\"address\":\"address\",\"name\":\"haha\",\"id\":1,\"email\":\"email\"}}";
try {
Map<String, Map<String, Object>> maps = objectMapper.readValue(json, Map.class);
System.out.println(maps.size());
Set<String> key = maps.keySet();
Iterator<String> iter = key.iterator();
while (iter.hasNext()) {
String field = iter.next();
System.out.println(field + ":" + maps.get(field));
}
} catch (JsonParseException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
//json日期的转换
public class CustomDateSerializer extends JsonSerializer<Date> {
@Override
public void serialize(Date value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
String formattedDate = formatter.format(value);
jgen.writeString(formattedDate);
}
}
@JsonSerialize(using = CustomDateSerializer.class)
public Date getCreateAt() {
return createAt;
}
public void timeJson(){
StringWriter sw = new StringWriter();
JsonGenerator gen = new JsonFactory().createJsonGenerator(sw);
JacksonUtil.getInstance().writeValue(gen, jsonlist);
gen.close();
String finalInfo = sw.toString();
System.out.println("finalinfo is:"+finalInfo );
}最后是Gson。它会让我们解析json数据变得更简单。下载地址：http://code.google.com/p/google-gson/downloads/list。其中gson-2.24.jar就是我们需要引用的。
以下举例几个最常用到转换：
pubic class UserInfo implements Serializable{
private String name;
private int age;
public void setName(String name){
this.name=name;
}
public String getName(){
return name;
}
public void setAge(int age){
this.age=age;
}
public int getAge(){
return age;
}
}
//将对象转换成json字符串
public void test1(){
Gson gson = new Gson();
String str = gson.toJson(UserInfo);
return str;
}
//将各集合转换成json字符串
public void test2(){
List<UserInfo> retList = new ArrayList<UserInfo>();
Gson gson = new Gson();
String str = gson.toJson(retList);
return str;
}
//将json字符串转换为对象
public void test3(){
String jsonData = "{\"username\":\"arthinking\",\"userId\":001}";
Gson gson = new Gson();
User user = gson.fromJson(jsonData, User.class);
System.out.println(user.getUsername());
System.out.println(user.getUserId());
}
//将json字符串转换为集合对象
public void test4(){
Gson gson = new Gson();
List<UserInfo> retList = gson.fromJson(jsonstr, new TypeToken<List<UserInfo>>(){}.getType());
} 想学习更多Jackson的使用，请参考：http://www.cnblogs.com/hoojo/archive/2011/04/22/2024628.html