FastJSON、Jackson和Gson用法

一、JSON规范
JSON是一个标准规范,用于数据交互,规范的中文文档如下:
http://www.json.org/json-zh.html
参看规范,来对比JSON类库处理结果。

二、fastjson的一些简要说明
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。http://code.alibabatech.com/wiki/display/FastJSON/Home
如果获得Fastjson?
SVN:http://code.alibabatech.com/svn/fastjson/trunk/
WIKI:http://code.alibabatech.com/wiki/display/FastJSON/Home
Issue Tracking:http://code.alibabatech.com/jira/browse/FASTJSON

三、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。

测试代码:

package dhp.com.test;

public class Userinfo {
	private String name;
	private int age;

	public Userinfo() {
		super();
	}

	public Userinfo(String name,int age) {
		super();
		this.name = name;
		this.age = 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;
	}
}

package dhp.com.test;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Vector;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONArray;
import com.alibaba.fastjson.JSONObject;
import com.alibaba.fastjson.serializer.SerializerFeature;

/**
 * fastjson 是一个性能很好的 Java 语言实现的 JSON 解析器和生成器,来自阿里巴巴的工程师开发。
 *  主要特点:
 * 1.快速FAST(比其它任何基于Java的解析器和生成器更快,包括jackson) 强大
 * (支持普通JDK类包括任意Java Bean
 * 2.Class、Collection、Map、Date或enum) 零依赖(没有依赖其它任何类库除了JDK)
 * 
 */
public class TestFastJson {
	public static void main(String[] args) {
		String json = "{\"name\":\"chenggang\",\"age\":24}";
		String arrayAyy = "[[\'马云',50],null,[\'马化腾',30]]";
		 //Entity2json("zhangsan",24);
		 //list2Json();
		 //Complexdata();
		   Deserialization(json);
		   DateFormate(new Date());
		 //Json2Eetity(json);
		 //String2JSONArray(arrayAyy);
	}

	// 实体转为Json
	public static void Entity2json(String name,int age) {
		Userinfo info = new Userinfo(name,age);
		String str_json = JSON.toJSONString(info); //
		System.out.println("实体转化为Json" + str_json);
	}

	// list转Json
	public static void list2Json() {
		List<Userinfo> list = new ArrayList<Userinfo>();
		Userinfo userinfo1 = new Userinfo("lisi",15);
		Userinfo userinfo2 = new Userinfo("wangwu",16);
		list.add(userinfo1);
		list.add(userinfo2);
		String json = JSON.toJSONString(list,true);
		System.out.println("List集合转json格式字符串 :" + json);
	}

	// 字符数组转化为JSon
	private static void String2JSONArray(String arrayAyy) {
		JSONArray array = JSONArray.parseArray(arrayAyy);
		System.out.println("数组:" + array);
		System.out.println("数组长度: " + array.size());
		Collection nuCon = new Vector();
		nuCon.add(null);
		array.removeAll(nuCon);
		System.out.println("数组:" + array);
		System.out.println("数组长度: " + array.size());
	}

	// 复杂数据类型
	public static void Complexdata() {
		HashMap<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);
		String jsonString = JSON.toJSONString(map);
		System.out.println("复杂数据类型:" + jsonString);
	}

	public static void Deserialization(String json) {
		Userinfo userInfo = JSON.parseObject(json,Userinfo.class);
		System.out.println("姓名是:" + userInfo.getName() + ",年龄是:" + userInfo.getAge());
	}

	// 格式话日期
	public static void DateFormate(Date date) {
		System.out.println("输出毫秒值:" + JSON.toJSONString(date));
		System.out.println("默认格式为:" + JSON.toJSONString(date,SerializerFeature.WriteDateUseDateFormat));
		System.out.println("自定义日期:"
				+ JSON.toJSONStringWithDateFormat(date,"yyyy-MM-dd",SerializerFeature.WriteDateUseDateFormat));
	}

	// Json转为实体
	private static void Json2Eetity(String json) {
		Userinfo userInfo = JSON.parseObject(json,Userinfo.class);
		System.out.println("输出对象的地址:" + userInfo.toString());
		System.out.println("输出对象的名字:" + userInfo.getName());
	}
}

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


四、Jackson提供了很多类和方法,而在序列化和反序列化中使用的最多的类则是ObjectMapper这个类,此类中提供了readTree(),readValue(),writeValueAsString()等方法用于转换。

package dhp.com.test2;

public class Name {
	private String firstName;
	private String lastName;

	public Name() {
	}

	public Name(String firstName,String lastName) {
		this.firstName = firstName;
		this.lastName = lastName;
	}

	public String getFirstName() {
		return firstName;
	}

	public void setFirstName(String firstName) {
		this.firstName = firstName;
	}

	public String getLastName() {
		return lastName;
	}

	public void setLastName(String lastName) {
		this.lastName = lastName;
	}

	public String toString() {
		return firstName + " " + lastName;
	}
}

package dhp.com.test2;

import java.util.Date;

public class Student {
	private int id;
	private Name name;
	private String className;
	private Date birthDay;

	public Student() {
	}

	public Student(int id,Name name,String className,Date birthDay) {
		super();
		this.id = id;
		this.name = name;
		this.className = className;
		this.birthDay = birthDay;
	}

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public Name getName() {
		return name;
	}

	public void setName(Name name) {
		this.name = name;
	}

	public Date getBirthDay() {
		return birthDay;
	}

	public void setBirthDay(Date birthDay) {
		this.birthDay = birthDay;
	}

	public String getClassName() {
		return className;
	}

	public void setClassName(String className) {
		this.className = className;
	}

	@Override
	public String toString() {
		return "Student [birthDay=" + birthDay + ",id=" + id + ",name=" + name + ",classname=" + className + "]";
	}
}

package dhp.com.test2;

import java.text.SimpleDateFormat;  
import java.util.ArrayList;  
import java.util.Date;  
import java.util.HashMap;  
import java.util.List;  
import java.util.Map;  
  
import org.codehaus.jackson.JsonGenerator;  
import org.codehaus.jackson.map.DeserializationConfig;  
import org.codehaus.jackson.map.ObjectMapper;  
import org.codehaus.jackson.map.SerializationConfig;  
import org.codehaus.jackson.map.annotate.JsonSerialize.Inclusion;  
import org.codehaus.jackson.type.TypeReference;  

public class TestJackson {
	public static ObjectMapper getDefaultObjectMapper() {  
        ObjectMapper mapper = new ObjectMapper();  
        //设置将对象转换成JSON字符串时候:包含的属性不能为空或"";    
        //Include.Include.ALWAYS 默认    
        //Include.NON_DEFAULT 属性为默认值不序列化    
        //Include.NON_EMPTY 属性为 空("")  或者为 NULL 都不序列化    
        //Include.NON_NULL 属性为NULL 不序列化    
        mapper.setSerializationInclusion(Inclusion.NON_EMPTY);  
        //设置将MAP转换为JSON时候只转换值不等于NULL的  
        mapper.configure(SerializationConfig.Feature.WRITE_NULL_MAP_VALUES,false);  
        //mapper.configure(JsonGenerator.Feature.ESCAPE_NON_ASCII,true);  
        mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));  
        //设置有属性不能映射成PO时不报错  
        mapper.disable(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES);  
        return mapper;  
    }  
    public static void main(String[] args) throws Exception{  
        //准备数据  
        Name name1 = new Name("zhang","san");  
        Name name2 = new Name("li","si");  
        Name name3 = new Name("wang","wu");  
        Student student1 = new Student(1,name1,"一班",new Date());    
        Student student2 = new Student(2,name2,"二班",new Date());    
        Student student3 = new Student(3,name3,"三班",new Date());    
        List<Student> studentList = new ArrayList<Student>();  
        studentList.add(student1);  
        studentList.add(student2);  
        studentList.add(student3);  
        Map<String,Student> studentMap = new HashMap<String,Student>();  
        studentMap.put("1",student1);  
        studentMap.put("2",student2);  
        studentMap.put("3",student3);  
        Student json2object = null;  
        List<Student> json2list = null;  
        Map<String,Student> json2map = null;  
        ObjectMapper mapper = getDefaultObjectMapper();  
          
        /* Object --> JSON */  
        String object4json = mapper.writeValueAsString(student1);  
        System.out.println("Object ----> JSON");  
        System.out.println(object4json);  
        System.out.println("------------------------------------------------------");  
          
        /* List<Object> --> JSON */  
        String listforjson = mapper.writeValueAsString(studentList);  
        System.out.println("List<Object> ----> JSON");  
        System.out.println(listforjson);  
        System.out.println("------------------------------------------------------");  
          
        /* Map<String,Object> ----> JSON */  
        String map4json = mapper.writeValueAsString(studentMap);  
        System.out.println("Map<String,Object> ----> JSON");  
        System.out.println(map4json);  
        System.out.println("------------------------------------------------------");  
          
        /* JSON --> Object */  
        json2object = mapper.readValue(object4json,Student.class);  
        System.out.println("JSON ----> Object");  
        System.out.println(json2object);  
        System.out.println("------------------------------------------------------");  
        /* JSON --> List<Object> */  
        json2list = mapper.readValue(listforjson,new TypeReference<List<Student>>() {});  
        System.out.println("JSON --> List<Object>");  
        System.out.println(json2list.toString());  
        System.out.println("------------------------------------------------------");  
        /* JSON --> Map<String,Object> */  
        json2map = mapper.readValue(map4json,new TypeReference<Map<String,Student>>() {});  
        System.out.println("JSON --> Map<String,Object>");  
        System.out.println(json2map.toString());  
    }  
}


注意:jackson渐次反序列化
此方法更灵活,可以只将用户感兴趣的Json串信息值提取出来。主要利用ObjectMapper提供的readTree和Jackson提供的JsonNode类来实现。

测试例子:

String test="{"results":[{"objectID":357,"geoPoints":[{"x":504604.59802246094,"y":305569.9150390625}]},{"objectID":358,"geoPoints":[{"x":504602.2680053711,"y":305554.43603515625}]}]}";

此Json串比较复杂,包含了嵌套数组的形式,具有通用性。

实现反序列化

JsonNode node= objectMapper.readTree(test);   //将Json串以树状结构读入内存
JsonNode contents=node.get("results");//得到results这个节点下的信息
for(int i=0;i<contents.size();i++) //遍历results下的信息,size()函数可以得节点所包含的的信息的个数,类似于数组的长度
{
System.out.println(contents.get(i).get("objectID").getIntValue()); //读取节点下的某个子节点的值
JsonNode geoNumber=contents.get(i).get("geoPoints");
for(int j=0;j<geoNumber.size();j++)   //循环遍历子节点下的信息
{
System.out.println(geoNumber.get(j).get("x").getDoubleValue()+" "+geoNumber.get(j).get("y").getDoubleValue());
}
}

在控制台下输出的结果是:
357
504604.59802246094 305569.9150390625
358
504602.2680053711 305554.43603515625
此方法类似于XML解析中的DOM方式解析,其好处是结构明细,便于提取想要的信息。当然,其缺点也和此方法一样:耗时费空间。

五、Gson是非常强大的API,它支持Java泛型,支持现成的JSON与Java对象的转换,只要对象的成员名称与JSON中的一致即可。如果针对Java bean和JSON要使用不同的名称,那么可以使用@SerializedName注解来映射JSON和Java类中的变量。

我们来看一个复杂示例,在JSON中含有嵌套对象以及数组,我们要将其映射到Java bean的属性(List、Map、Array类型等)中。

{
  "empID": 100,"name": "David","permanent": false,"address": {
    "street": "BTM 1st Stage","city": "Bangalore","zipcode": 560100
  },"phoneNumbers": [
    123456,987654
  ],"role": "Manager","cities": [
    "Los Angeles","New York"
  ],"properties": {
    "age": "28 years","salary": "1000 Rs"
  }
}

建立Java bean类,将JSON转换为Java对象。
Employee.java

package com.journaldev.json.model;
 
import java.util.Arrays;
import java.util.List;
import java.util.Map;
 
import com.google.gson.annotations.SerializedName;
 
public class Employee {
 
    @SerializedName("empID")
    private int id;
    private String name;
    private boolean permanent;
    private Address address;
    private long[] phoneNumbers;
    private String role;
    private List<String> cities;
    private Map<String,String> properties;
 
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public boolean isPermanent() {
        return permanent;
    }
    public void setPermanent(boolean permanent) {
        this.permanent = permanent;
    }
    public Address getAddress() {
        return address;
    }
    public void setAddress(Address address) {
        this.address = address;
    }
    public long[] getPhoneNumbers() {
        return phoneNumbers;
    }
    public void setPhoneNumbers(long[] phoneNumbers) {
        this.phoneNumbers = phoneNumbers;
    }
    public String getRole() {
        return role;
    }
    public void setRole(String role) {
        this.role = role;
    }
 
    @Override
    public String toString(){
        StringBuilder sb = new StringBuilder();
        sb.append("***** Employee Details *****n");
        sb.append("ID="+getId()+"n");
        sb.append("Name="+getName()+"n");
        sb.append("Permanent="+isPermanent()+"n");
        sb.append("Role="+getRole()+"n");
        sb.append("Phone Numbers="+Arrays.toString(getPhoneNumbers())+"n");
        sb.append("Address="+getAddress()+"n");
        sb.append("Cities="+Arrays.toString(getCities().toArray())+"n");
        sb.append("Properties="+getProperties()+"n");
        sb.append("*****************************");
 
        return sb.toString();
    }
    public List<String> getCities() {
        return cities;
    }
    public void setCities(List<String> cities) {
        this.cities = cities;
    }
    public Map<String,String> getProperties() {
        return properties;
    }
    public void setProperties(Map<String,String> properties) {
        this.properties = properties;
    }
}

Address.java

package com.journaldev.json.model;
 
public class Address {
 
    private String street;
    private String city;
    private int zipcode;
 
    public String getStreet() {
        return street;
    }
    public void setStreet(String street) {
        this.street = street;
    }
    public String getCity() {
        return city;
    }
    public void setCity(String city) {
        this.city = city;
    }
    public int getZipcode() {
        return zipcode;
    }
    public void setZipcode(int zipcode) {
        this.zipcode = zipcode;
    }
 
    @Override
    public String toString(){
        return getStreet() + ","+getCity()+","+getZipcode();
    }
}

下面是Java程序,展示了如何将JSON转换为Java对象,反之亦然。
EmployeeGsonExample.java

package com.journaldev.json.gson;
 
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
 
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.journaldev.json.model.Address;
import com.journaldev.json.model.Employee;
 
public class EmployeeGsonExample {
 
    public static void main(String[] args) throws IOException {
        Employee emp = createEmployee();
 
        // Get Gson object
        Gson gson = new GsonBuilder().setPrettyPrinting().create();
 
        // read JSON file data as String
        String fileData = new String(Files.readAllBytes(Paths
                .get("employee.txt")));
 
        // parse json string to object
        Employee emp1 = gson.fromJson(fileData,Employee.class);
 
        // print object data
        System.out.println("nnEmployee Objectnn" + emp1);
 
        // create JSON String from Object
        String jsonEmp = gson.toJson(emp);
        System.out.print(jsonEmp);
 
    }
 
    public static Employee createEmployee() {
 
        Employee emp = new Employee();
        emp.setId(100);
        emp.setName("David");
        emp.setPermanent(false);
        emp.setPhoneNumbers(new long[] { 123456,987654 });
        emp.setRole("Manager");
 
        Address add = new Address();
        add.setCity("Bangalore");
        add.setStreet("BTM 1st Stage");
        add.setZipcode(560100);
        emp.setAddress(add);
 
        List<String> cities = new ArrayList<String>();
        cities.add("Los Angeles");
        cities.add("New York");
        emp.setCities(cities);
 
        Map<String,String> props = new HashMap<String,String>();
        props.put("salary","1000 Rs");
        props.put("age","28 years");
        emp.setProperties(props);
 
        return emp;
    }
}

Gson是主类,它暴露出fromJson()和toJson()方法进行转换工作,对于默认实现,可以直接创建对象,也可以使用GsonBuilder类提供的实用选项进行转换,比如整齐打印,字段命名转换,排除字段,日期格式化,等等。
当运行以上程序时,可以看到以下Java对象的输出。

Employee Object
 
***** Employee Details *****
ID=100
Name=David
Permanent=false
Role=Manager
Phone Numbers=[123456,987654]
Address=BTM 1st Stage,Bangalore,560100
Cities=[Los Angeles,New York]
Properties={age=28 years,salary=1000 Rs}
*****************************

你可以看到,使用Gson是多么的容易,这就是为什么它在JSON处理方面如此风靡。
以上的JSON处理方式是我们所熟知的对象模型,因为整个JSON被一次性的转换为对象了,在大多数情况下这足够了,然而如果JSON确实非常庞大,我们不想将其全部一次性置入内存,Gson也提供了Streaming API。
我们来看一个例子,它展示了如何使用Streaming API进行JSON到Java对象的转换。
EmployeeGsonReader.java

package com.journaldev.json.gson;
 
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
 
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import com.journaldev.json.model.Address;
import com.journaldev.json.model.Employee;
 
public class EmployeeGsonReader {
 
    public static void main(String[] args) throws IOException {
        InputStream is = new FileInputStream("employee.txt");
        InputStreamReader isr = new InputStreamReader(is);
 
        //create JsonReader object
        JsonReader reader = new JsonReader(isr);
 
        //create objects
        Employee emp = new Employee();
        Address add = new Address();
        emp.setAddress(add);
        List<Long> phoneNums = new ArrayList<Long>();
        emp.setCities(new ArrayList<String>());
        emp.setProperties(new HashMap<String,String>());
        String key = null;
        boolean insidePropertiesObj=false;
 
        key = parseJSON(reader,emp,phoneNums,key,insidePropertiesObj);
 
        long[] nums = new long[phoneNums.size()];
        int index = 0;
        for(Long l :phoneNums){
            nums[index++] = l;
        }
        emp.setPhoneNumbers(nums);
 
        reader.close();
        //print employee object
        System.out.println("Employee Objectnn"+emp);
    }
 
    private static String parseJSON(JsonReader reader,Employee emp,List<Long> phoneNums,String key,boolean insidePropertiesObj) throws IOException {
 
        //loop to read all tokens
                while(reader.hasNext()){
                    //get next token
                    JsonToken token = reader.peek();
 
                    switch(token){
                    case BEGIN_OBJECT:
                        reader.beginObject();
                        if("address".equals(key) || "properties".equals(key)){
                            while(reader.hasNext()){
                            parseJSON(reader,insidePropertiesObj);
                            }
                            reader.endObject();
                        }
                        break;
                    case END_OBJECT:
                        reader.endObject();
                        if(insidePropertiesObj) insidePropertiesObj=false;
                        break;
                    case BEGIN_ARRAY:
                        reader.beginArray();
                        if("phoneNumbers".equals(key) || "cities".equals(key)){
                            while(reader.hasNext()){
                                parseJSON(reader,insidePropertiesObj);
                                }
                            reader.endArray();
                        }
                        break;
                    case END_ARRAY:
                        reader.endArray();
                        break;
                    case NAME:
                        key = reader.nextName();
                        if("properties".equals(key)) insidePropertiesObj=true;
                        break;
                    case BOOLEAN:
                        if("permanent".equals(key)) emp.setPermanent(reader.nextBoolean());
                        else{
                            System.out.println("Unknown item found with key="+key);
                            //skip value to ignore it
                            reader.skipValue();
                        }
                        break;
                    case NUMBER:
                        if("empID".equals(key)) emp.setId(reader.nextInt());
                        else if("phoneNumbers".equals(key)) phoneNums.add(reader.nextLong());
                        else if("zipcode".equals(key)) emp.getAddress().setZipcode(reader.nextInt());
                        else {
                            System.out.println("Unknown item found with key="+key);
                            //skip value to ignore it
                            reader.skipValue();
                        }
                        break;
                    case STRING:
                        setStringValues(emp,reader.nextString(),insidePropertiesObj);
                        break;
                    case NULL:
                        System.out.println("Null value for key"+key);
                        reader.nextNull();
                        break;
                    case END_DOCUMENT:
                        System.out.println("End of Document Reached");
                        break;
                    default:
                        System.out.println("This part will never execute");
                        break;
 
                    }
                }
                return key;
    }
 
    private static void setStringValues(Employee emp,String value,boolean insidePropertiesObj) {
        if("name".equals(key)) emp.setName(value);
        else if("role".equals(key)) emp.setRole(value);
        else if("cities".equals(key)) emp.getCities().add(value);
        else if ("street".equals(key)) emp.getAddress().setStreet(value);
        else if("city".equals(key)) emp.getAddress().setCity(value);
        else{
            //add to emp properties map
            if(insidePropertiesObj){
                emp.getProperties().put(key,value);
            }else{
                System.out.println("Unknown data found with key="+key+" value="+value);
            }
 
        }
    }
 
}

由于JSON是一个递归语言(译注:JSON本身并不是“语言”,而是一种表示方法),我们也需要针对数组和嵌套对象递归地调用解析方法。JsonToken是JsonReader中next()方法所返回的Java枚举类型,我们可以用其配合条件逻辑或switch case语句进行转换工作。根据以上代码,你应该能够理解这不是一个简单的实现,如果JSON确实非常复杂,那么代码将会变得极难维护,所以要避免使用这种方式,除非没有其他出路。


我们来看一下如何使用Gson Streaming API写出Employee对象。
EmployeeGsonWriter.java

package com.journaldev.json.gson;
 
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.util.Set;
 
import com.google.gson.stream.JsonWriter;
import com.journaldev.json.model.Employee;
 
public class EmployeeGsonWriter {
 
    public static void main(String[] args) throws IOException {
        Employee emp = EmployeeGsonExample.createEmployee();
 
        //writing on console,we can initialize with FileOutputStream to write to file
        OutputStreamWriter out = new OutputStreamWriter(System.out);
        JsonWriter writer = new JsonWriter(out);
        //set indentation for pretty print
        writer.setIndent("t");
        //start writing
        writer.beginObject(); //{
        writer.name("id").value(emp.getId()); // "id": 123
        writer.name("name").value(emp.getName()); // "name": "David"
        writer.name("permanent").value(emp.isPermanent()); // "permanent": false
        writer.name("address").beginObject(); // "address": {
            writer.name("street").value(emp.getAddress().getStreet()); // "street": "BTM 1st Stage"
            writer.name("city").value(emp.getAddress().getCity()); // "city": "Bangalore"
            writer.name("zipcode").value(emp.getAddress().getZipcode()); // "zipcode": 560100
            writer.endObject(); // }
        writer.name("phoneNumbers").beginArray(); // "phoneNumbers": [
            for(long num : emp.getPhoneNumbers()) writer.value(num); //123456,987654
            writer.endArray(); // ]
        writer.name("role").value(emp.getRole()); // "role": "Manager"
        writer.name("cities").beginArray(); // "cities": [
            for(String c : emp.getCities()) writer.value(c); //"Los Angeles","New York"
            writer.endArray(); // ]
        writer.name("properties").beginObject(); //"properties": {
            Set<String> keySet = emp.getProperties().keySet();
            for(String key : keySet) writer.name("key").value(emp.getProperties().get(key));//"age": "28 years","salary": "1000 Rs"
            writer.endObject(); // }
        writer.endObject(); // }
 
        writer.flush();
 
        //close writer
        writer.close();
 
    }
 
}

从Java对象到JSON的转换,与使用streaming API解析相比,相对容易一些,默认情况下JsonWriter会以一种紧凑的格式写入JSON,但也可以设置缩进进行整齐打印。

这就是Gson API演示教程的所有内容,如果你遇到任何问题,请告诉我。以下链接可以下载项目,你可以玩一玩Gson提供的多种选项。 http://www.journaldev.com/?wpdmact=process&did=MzAuaG90bGluaw== 原文链接: Pankaj Kumar 翻译: ImportNew.com - Justin Wu 译文链接: http://www.importnew.com/14509.html

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