java json 操作 java对json的操作

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：javascript:void(0)。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:1
firstName:Bill
lastName:Gates
-----------
id:1
firstName:George
lastName:Bush
-----------
id:3
firstName:Thomas
lastName: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}