[J2EE]java操作json

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一、JSON语法

JSON:JavaScript 对象表示法(JavaScript Object Notation),JSON 是存储和交换文本信息的语法。类似 XML,但 比 XML 更小、更快,更易解析。
JSON 数据的书写格式是:名称/值对。
名称/值对包括字段名称(在双引号中),后面写一个冒号,然后是值:

"firstName" : "John"

JSON 数组在方括号中书写:
数组可包含多个对象:

{    "employees": [        { "firstName":"John" , "lastName":"Doe" },        { "firstName":"Anna" , "lastName":"Smith" },        { "firstName":"Peter" , "lastName":"Jones" }     ]}

二、GSON简介

Gson 是 Google 提供的用来在 Java 对象和 JSON 数据之间进行映射的 Java 类库。可以将一个 JSON 字符串转成一个 Java 对象,或者反过来。下载jar包:http://download.csdn.net/detail/yang_xing_/8363795。在eclipse中新建一个java project,把gson-2.2.4.jar引入。在工程根目录下创建一个employee.json文件:

{    "department":"design",    "employees": [        { "firstName":"Bill" , "lastName":"Gates" },        { "firstName":"George" , "lastName":"Bush" },        { "firstName":"Thomas" , "lastName":"Carter" }    ]}

二、读取json

首先创建一个json解析器,然后创建一个JsonObject对象,之后调用get方法访问属性值:

package ucas.json.test;import java.io.File;import java.io.FileNotFoundException;import java.io.FileReader;import com.google.gson.JsonIOException;import com.google.gson.JsonObject;import com.google.gson.JsonParser;import com.google.gson.JsonSyntaxException;public class JsonTest {    public static void main(String[] args) {        try {            JsonParser jParser = new JsonParser();            JsonObject jObject = (JsonObject) jParser                    .parse(new FileReader("employee.json"));            System.out.println(jObject.get("department").getAsString());            System.out.println(jObject.get("employees"));        } catch (JsonIOException e) {            e.printStackTrace();        } catch (JsonSyntaxException e) {            e.printStackTrace();        } catch (FileNotFoundException e) {            e.printStackTrace();        }    }}

输出结果:

design[{"firstName":"Bill","lastName":"Gates"},{"firstName":"George","lastName":"Bush"},{"firstName":"Thomas","lastName":"Carter"}]

可以看到”employees”属性为数组,转化为JsonArray然后循环读取:

package ucas.json.test;import java.io.File;import java.io.FileNotFoundException;import java.io.FileReader;import com.google.gson.JsonArray;import com.google.gson.JsonIOException;import com.google.gson.JsonObject;import com.google.gson.JsonParser;import com.google.gson.JsonSyntaxException;public class JsonTest {    public static void main(String[] args) {        try {            JsonParser jParser = new JsonParser();            JsonObject jObject = (JsonObject) jParser                    .parse(new FileReader("employee.json"));            System.out.println(jObject.get("department").getAsString());            JsonArray jArray=(JsonArray) jObject.get("employees");            for (int i = 0; i < jArray.size(); i++) {                System.out.println("-----------");                JsonObject jObject2=(JsonObject) jArray.get(i);                System.out.println("id:"+jObject2.get("id").getAsString());                System.out.println("firstName:"+jObject2.get("firstName").getAsString());                System.out.println("lastName:"+jObject2.get("lastName").getAsString());            }        } catch (JsonIOException e) {            e.printStackTrace();        } catch (JsonSyntaxException e) {            e.printStackTrace();        } catch (FileNotFoundException e) {            e.printStackTrace();        }    }}

输出结果:

design-----------id:1firstName:BilllastName:Gates-----------id:1firstName:GeorgelastName:Bush-----------id:3firstName:ThomaslastName:Carter

三、创建json

创建json对象,添加属性使用addProperty方法,添加对象使用add方法,例子:

import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;import java.io.OutputStreamWriter;import com.google.gson.JsonArray;import com.google.gson.JsonObject;public class JsonDemo2 {    public static void main(String[] args) {        // 创建json数据        JsonObject jsonObject = new JsonObject();        jsonObject.addProperty("cat", "it");        JsonArray jArray = new JsonArray();        JsonObject lan1 = new JsonObject();        lan1.addProperty("id", 1);        lan1.addProperty("name", "java");        lan1.addProperty("ide", "eclipse");        jArray.add(lan1);        JsonObject lan2 = new JsonObject();        lan2.addProperty("id", 2);        lan2.addProperty("name", "C++");        lan2.addProperty("ide", "VC6.0");        jArray.add(lan2);        JsonObject lan3 = new JsonObject();        lan3.addProperty("id", 3);        lan3.addProperty("name", "C#");        lan3.addProperty("ide", "Visual Studio");        jArray.add(lan3);        JsonObject lan4 = new JsonObject();        lan4.addProperty("id", 4);        lan4.addProperty("name", "Swift");        lan4.addProperty("ide", "Xcode");        jArray.add(lan4);        jsonObject.add("languages", jArray);        jsonObject.addProperty("pop", true);        System.out.println(jsonObject);        File jsonFile = new File("test.json");        try {            jsonFile.createNewFile();            FileOutputStream fos = new FileOutputStream(jsonFile);            OutputStreamWriter osq = new OutputStreamWriter(fos);            BufferedWriter bfw = new BufferedWriter(osq);            bfw.write(jsonObject.toString());            bfw.close();            osq.close();            fos.close();        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }}

这样在工程根目录下会生成一个test.json的文件:

{"cat":"it","languages":[{"id":1,"name":"哈哈","ide":"eclipse\n"},{"id":2,"name":"C++","ide":"VC6.0"},{"id":3,"name":"C#","ide":"Visual Studio"},{"id":4,"name":"Swift","ide":"Xcode"}],"pop":true}

总结:

  1. json简介和语法可以参考json官网http://www.json.org/和W3C教程JSON教程
  2. 操作json的库有很多,可以选择学习。
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