Android笔记（五十） Android中的JSON数据

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"
}