利用JsonReade和JsonReader实现json解析和写数据
前面讲过调用谷歌的json包来对json数据进行解析，随着android的发展现在手机系统都是android4.0以上版本了，因此可以直接调用sdk 中的JsonReader来解析json数据了。json数据的解析成现有的类，这些类通常是javaBean类，通过查看官方的文档将其文档的例子完善了下如下：
json数据：
[
{
"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
}
}
]
需要解析出来的类：
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的类：调用readJsonStream函数就可以解析出该json文件，该解析和xml解析相似，开头分reader.beginArray 和reader.beginObject 第一个是接下来解析一个数组，通常里面嵌套解析一个解析另外个对象的函数，后面一个就是解析对象，然后就是相应的end结束语句,且对象里面含有对象，因此对象的读取是嵌套实现的：
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 为要读取的文件的输入流
*/
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) {//后面一个判断geo的值不为空，因为有可能为空
geo = readDoublesArray(reader);
} else if (name.equals("user")) {
user = readUser(reader);
} else {
reader.skipValue();
}
}
reader.endObject();
return new MyMessage(id, text, user, geo);
}
//读取double型的数组，主要是读取geo项的数组
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对象，存储的是MyMessage对象，下面我们利用JsonWriter来自己写json数据：写的内容就是上面的得到的list里面的MyMessage对象,写的内容和读的一模一样：下面给出写的类：
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();
}
}
主函数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);
//读取data目录下的json数据存储到集合中
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("第一个"+list.get(0).id);
} catch (FileNotFoundException e) {
System.out.println("文件没找到");
e.printStackTrace();
} catch (IOException e) {
System.out.println("读取文件失败");
e.printStackTrace();
}
//将上面得到的MyMessage对象的数据写入成json数据
try {
OutputStream outputStream = openFileOutput("message", Context.MODE_PRIVATE);
MyMessageJsonWriter myMessageJsonWriter = new MyMessageJsonWriter();
myMessageJsonWriter.writeJsonStream(outputStream, list);
} catch (Exception e) {
e.printStackTrace();
}
}
}
