Android笔记（五十） Android中的JSON数据

时间：2021-07-25 21:11:44

JSON是什么：

JSON是轻量级的文本数据交换格式

JSON独立于语言和平台

JSON具有自我描述性，更容易理解

JSON语法：

数据在名称/值对中

数据由逗号分割

大括号表示对象

中括号表示数组

JSON使用：

MainActivity.java

package cn.lixyz.jsontest.activity;

import java.io.BufferedReader;

import java.io.File;

import java.io.FileWriter;

import java.io.IOException;

import java.io.InputStreamReader;

import java.io.UnsupportedEncodingException;

import org.json.JSONArray;

import org.json.JSONException;

import org.json.JSONObject;

import android.app.Activity;

import android.os.Bundle;

import android.os.Environment;

import android.util.Log;

import android.view.View;

import cn.lixyz.jsontest.R;

public class MainActivity extends Activity {

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

    }

    public void clickButton(View v) {

        switch (v.getId()) {

        case R.id.bt_readjson:

            readJson();

            break;

        case R.id.bt_writejson:

            writeJson();

            break;

        }

    }

    // 往sdcard中写入文件

    private void writeJson() {

        // 创建一个json对象

        JSONObject root = new JSONObject();

        try {

            // 使用put(kay,value)插入元素

            root.put("class", "三年二班");

            // 常见若干对象，用以加入数组

            JSONObject student1 = new JSONObject();

            student1.put("id", 1);

            student1.put("name", "张三");

            student1.put("age", 10);

            JSONObject student2 = new JSONObject();

            student2.put("id", 2);

            student2.put("name", "李四");

            student2.put("age", 11);

            JSONObject student3 = new JSONObject();

            student3.put("id", 3);

            student3.put("name", "王五");

            student3.put("age", 13);

            JSONObject student4 = new JSONObject();

            student4.put("id", 4);

            student4.put("name", "赵六");

            student4.put("age", 14);

            JSONObject student5 = new JSONObject();

            student5.put("id", 5);

            student5.put("name", "孙七");

            student5.put("age", 15);

            JSONObject student6 = new JSONObject();

            student6.put("id", 6);

            student6.put("name", "刘八");

            student6.put("age", 16);

            // 创建一个json数组

            JSONArray array = new JSONArray();

            // 将之前创建的json对象添加进来

            array.put(student1);

            array.put(student2);

            array.put(student3);

            array.put(student4);

            array.put(student5);

            array.put(student6);

            // 将json数组添加

            root.put("student", array);

            Log.d("TTTT", array.toString());

        } catch (JSONException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

        String packageName = this.getPackageName();

        String jsonFileName = "json.json";

        String sdCardPath = Environment.getExternalStorageDirectory().toString();

        File sdCardPackagePath = new File(sdCardPath + "/" + packageName);

        if (!sdCardPackagePath.exists()) {

            if (sdCardPackagePath.mkdir()) {

                Log.d("TTTT", "创建目录成功");

            } else {

                Log.d("TTTT", "创建目录不成功");

            }

        }

        File jsonFile = new File(sdCardPackagePath + "/" + jsonFileName);

        if (!jsonFile.exists()) {

            try {

                if (jsonFile.createNewFile()) {

                    Log.d("TTTT", "创建文件成功");

                } else {

                    Log.d("TTTT", "创建文件失败");

                }

            } catch (IOException e) {

                // TODO Auto-generated catch block

                e.printStackTrace();

            }

        }

        try {

            // 将json数据写入文件

            FileWriter fileWriter = new FileWriter(jsonFile);

            fileWriter.write(root.toString());

            fileWriter.flush();

        } catch (IOException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

    // 读取assets目录中的json文件

    private void readJson() {

        try {

            // 读取assets目录下的json文件

            InputStreamReader isr = new InputStreamReader(getAssets().open("test.json"), "UTF-8");

            BufferedReader br = new BufferedReader(isr);

            String line;

            StringBuilder builder = new StringBuilder();

            while ((line = br.readLine()) != null) {

                builder.append(line);

            }

            br.close();

            // 获取到json文件中的对象

            JSONObject root = new JSONObject(builder.toString());

            // 使用getString(key)方式获取value

            Log.d("TTTT", "class=" + root.getString("class"));

            // 获取json数组

            JSONArray array = root.getJSONArray("student");

            for (int i = 0; i < array.length(); i++) {

                JSONObject student = array.getJSONObject(i);

                Log.d("TTTT", "id=" + student.getInt("id") + ",name=" + student.getString("name") + ",age="

                        + student.getInt("age"));

            }

        } catch (UnsupportedEncodingException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        } catch (IOException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        } catch (JSONException e) {

            // TODO Auto-generated catch block

            e.printStackTrace();

        }

    }

}

activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical"

    android:paddingBottom="@dimen/activity_vertical_margin"

    android:paddingLeft="@dimen/activity_horizontal_margin"

    android:paddingRight="@dimen/activity_horizontal_margin"

    android:paddingTop="@dimen/activity_vertical_margin"

    tools:context="cn.lixyz.jsontest.activity.MainActivity" >

    <Button

        android:id="@+id/bt_writejson"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:onClick="clickButton"

        android:text="@string/writejson" />

    <Button

        android:id="@+id/bt_readjson"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:onClick="clickButton"

        android:text="@string/readjson" />

</LinearLayout>

/assets/test.json

{

    "student":[

        {"id":1,"name":"张三","age":10},

        {"id":2,"name":"李四","age":11},

        {"id":3,"name":"王五","age":12},

        {"id":4,"name":"赵六","age":13},

        {"id":5,"name":"孙七","age":14},

        {"id":6,"name":"刘八","age":15},

    ],

    "class":"三年二班"

}

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