前面講過調用谷歌的json包來對json數據進行解析，隨着android的發展現在手機系統都是android4.0以上版本了，因此可以直接調用sdk 中的JsonReader來解析json數據了。json數據的解析成現有的類，這些類通常是javaBean類，通過查看官方的文檔將其文檔的例子完善了下如下：
json數據：
[
{
"id": 912345678901,
"text": "How do I read JSON on Android?",
"geo": null,
"user":
{
"name": "android_newb",
"followers_count": 41
}
},
{
"id": 912345678902,
"text": "@android_newb just use android.util.JsonReader!",
"geo": [50.454722, -104.606667],
"user":
{
"name": "jesse",
"followers_count": 2
}
}
]
需要解析出來的類：
package com.example.user.myjosn;
import java.util.List;
/**
* Created by user on 2016/10/18.
*/
public class MyMessage {
long id;
String text;
List geo;
User user;
public MyMessage(long id,String text, User user, List geo)
{
this.id= id;
this.user= user;
this.geo = geo;
this.text = text;
}
}
class User
{
public User(String name,int count)
{
this.name= name;
this.followers_count = count;
}
String name;
int followers_count;
}
解析json的類：調用readJsonStream函數就可以解析出該json文件，該解析和xml解析相似，開頭分reader.beginArray 和reader.beginObject 第一個是接下來解析一個數組，通常里面嵌套解析一個解析另外個對象的函數，后面一個就是解析對象，然后就是相應的end結束語句,且對象里面含有對象，因此對象的讀取是嵌套實現的：
package com.example.user.myjosn;
import android.os.Message;
import android.util.JsonReader;
import android.util.JsonToken;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
/**
* Created by user on 2016/10/18.
*/
public class MyMessageJsonReader {
/*
in 為要讀取的文件的輸入流
*/
public List readJsonStream(InputStream in) throws IOException {
JsonReader reader = new JsonReader(new InputStreamReader(in, "UTF-8"));
try {
return readMessagesArray(reader);
}
finally{
reader.close();
}
}
public List readMessagesArray(JsonReader reader) throws IOException {
List messages = new ArrayList();
reader.beginArray();
while (reader.hasNext()) {
messages.add(readMessage(reader));
}
reader.endArray();
return messages;
}
public MyMessage readMessage(JsonReader reader) throws IOException {
long id = -1;
String text = null;
User user = null;
List geo = null;
reader.beginObject();
while (reader.hasNext()) {
String name = reader.nextName();
if (name.equals("id")) {
id = reader.nextLong();
} else if (name.equals("text")) {
text = reader.nextString();
} else if (name.equals("geo") && reader.peek() != JsonToken.NULL) {//后面一個判斷geo的值不為空，因為有可能為空
geo = readDoublesArray(reader);
} else if (name.equals("user")) {
user = readUser(reader);
} else {
reader.skipValue();
}
}
reader.endObject();
return new MyMessage(id, text, user, geo);
}
//讀取double型的數組，主要是讀取geo項的數組
public List readDoublesArray(JsonReader reader) throws IOException {
List doubles = new ArrayList();
reader.beginArray();
while (reader.hasNext()) {
doubles.add(reader.nextDouble());
}
reader.endArray();
return doubles;
}
public User readUser(JsonReader reader) throws IOException {
String username = null;
int followersCount = -1;
reader.beginObject();
while (reader.hasNext()) {
String name = reader.nextName();
if (name.equals("name")) {
username = reader.nextString();
} else if (name.equals("followers_count")) {
followersCount = reader.nextInt();
} else {
reader.skipValue();
}
}
reader.endObject();
return new User(username, followersCount);
}
}
解析完了后得到了list對象，存儲的是MyMessage對象，下面我們利用JsonWriter來自己寫json數據：寫的內容就是上面的得到的list里面的MyMessage對象,寫的內容和讀的一模一樣：下面給出寫的類：
package com.example.user.myjosn;
import android.util.JsonWriter;
import java.io.IOException;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.util.List;
/**
* Created by user on 2016/10/18.
*/
public class MyMessageJsonWriter {
public void writeJsonStream(OutputStream out, List messages) throws IOException {
JsonWriter writer = new JsonWriter(new OutputStreamWriter(out, "UTF-8"));
writer.setIndent(" ");
writeMessagesArray(writer, messages);
writer.close();
}
public void writeMessagesArray(JsonWriter writer, List messages) throws IOException {
writer.beginArray();
for (Object message : messages) {
writeMessage(writer,(MyMessage) message);
}
writer.endArray();
}
public void writeMessage(JsonWriter writer, MyMessage message) throws IOException {
writer.beginObject();
writer.name("id").value(message.getId());
writer.name("text").value(message.getText());
if (message.getGeo() != null) {
writer.name("geo");
writeDoublesArray(writer, message.getGeo());
} else {
writer.name("geo").nullValue();
}
writer.name("user");
writeUser(writer, message.getUser());
writer.endObject();
}
public void writeUser(JsonWriter writer, User user) throws IOException {
writer.beginObject();
writer.name("name").value(user.getName());
writer.name("followers_count").value(user.getFollowers_count());
writer.endObject();
}
public void writeDoublesArray(JsonWriter writer, List doubles) throws IOException {
writer.beginArray();
for (Object value : doubles) {
writer.value((Double)value);
}
writer.endArray();
}
}
主函數Activity:
package com.example.user.myjosn;
import android.content.Context;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
ArrayList<MyMessage> list;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//讀取data目錄下的json數據存儲到集合中
try {
InputStream in = new FileInputStream( "data/data/com.example.user.myjosn/files/jsondemo.txt");
MyMessageJsonReader mJson = new MyMessageJsonReader();
list = (ArrayList<MyMessage>) mJson.readJsonStream(in);
System.out.println("第一個"+list.get(0).id);
} catch (FileNotFoundException e) {
System.out.println("文件沒找到");
e.printStackTrace();
} catch (IOException e) {
System.out.println("讀取文件失敗");
e.printStackTrace();
}
//將上面得到的MyMessage對象的數據寫入成json數據
try {
OutputStream outputStream = openFileOutput("message", Context.MODE_PRIVATE);
MyMessageJsonWriter myMessageJsonWriter = new MyMessageJsonWriter();
myMessageJsonWriter.writeJsonStream(outputStream, list);
} catch (Exception e) {
e.printStackTrace();
}
}
}