如何缓存解析的JSON用于离线使用 [英] How to Cache Parsed JSON for Offline usage
问题描述
我已经JSON解析成功,但现在我想缓存它离线使用,即使是网络不可用,如果有任何新的项目来了,我想缓存这一点。
和什么是缓存数据的最佳选择? 共享preferences
或 SQLite数据库
下面是我的code,而我使用到JSON解析:
公共类MainActivity延伸活动{
ArrayList的<演员> actorsList;
ActorAdapter适配器;
@覆盖
保护无效的onCreate(包savedInstanceState){
super.onCreate(savedInstanceState);
的setContentView(R.layout.activity_main);
actorsList =新的ArrayList<演员>();
新JSONAsyncTask()执行(http://microblogging.wingnity.com/JSONParsingTutorial/jsonActors);
ListView控件列表视图=(ListView控件)findViewById(R.id.list);
适配器=新ActorAdapter(getApplicationContext(),R.layout.row,actorsList);
listview.setAdapter(适配器);
listview.setOnItemClickListener(新OnItemClickListener(){
@覆盖
公共无效onItemClick(适配器视图<>为arg0,查看ARG1,INT位置,
长ID){
// TODO自动生成方法存根
Toast.makeText(getApplicationContext(),actorsList.get(位置).getName(),Toast.LENGTH_LONG).show();
}
});
}
类JSONAsyncTask扩展的AsyncTask<字符串,太虚,布尔> {
ProgressDialog对话框;
@覆盖
在preExecute保护无效(){
super.on preExecute();
对话框=新ProgressDialog(MainActivity.this);
dialog.setMessage(载入中,请稍候);
dialog.setTitle(连接服务器);
dialog.show();
dialog.setCancelable(假);
}
@覆盖
保护布尔doInBackground(字符串...网址){
尝试 {
// ------------------>>
HTTPGET httppost =新HTTPGET(网址[0]);
HttpClient的HttpClient的=新DefaultHttpClient();
HTT presponse响应= httpclient.execute(httppost);
//状态行STAT = response.getStatusLine();
。INT状态= response.getStatusLine()的getStatus code();
如果(状态== 200){
HttpEntity实体= response.getEntity();
字符串数据= EntityUtils.toString(实体);
JSONObject的jsono =新的JSONObject(数据);
JSONArray jarray = jsono.getJSONArray(演员);
的for(int i = 0; I< jarray.length();我++){
的JSONObject对象= jarray.getJSONObject(我);
演员演员=新演员();
actor.setName(object.getString(名字));
actor.setDescription(object.getString(说明));
actorsList.add(演员);
}
返回true;
}
// ------------------>>
}赶上(ParseException的E1){
e1.printStackTrace();
}赶上(IOException异常E){
e.printStackTrace();
}赶上(JSONException E){
e.printStackTrace();
}
返回false;
}
保护无效onPostExecute(布尔结果){
dialog.cancel();
adapter.notifyDataSetChanged();
如果(结果==假)
Toast.makeText(getApplicationContext(),无法获取来自服务器的数据,Toast.LENGTH_LONG).show();
}
}
}
为什么不直接使用它像这样保存到你的应用程序的缓存文件夹:
字符串路径= Environment.getExternalStorageDirectory()+文件分割符+缓存+文件分割符;
文件DIR =新的文件(路径);
如果(!dir.exists()){
dir.mkdirs();
}
路径+ =数据;
文件数据=新的文件(路径);
如果(!data.createNewFile()){
data.delete();
data.createNewFile();
}
ObjectOutputStream的ObjectOutputStream的=新的ObjectOutputStream(新的FileOutputStream(数据));
objectOutputStream.writeObject(actorsList);
objectOutputStream.close();
和之后,你可以使用在任何时候读它:
名单,其中;>名单= NULL;
文件数据=新的文件(路径);
尝试 {
如果(data.exists()){
ObjectInputStream的ObjectInputStream的=新的ObjectInputStream(新的FileInputStream(数据));
名单=(名单<对象>)objectInputStream.readObject();
objectInputStream.close();
}
}赶上(IOException异常E){
e.printStackTrace();
}赶上(ClassNotFoundException异常E){
e.printStackTrace();
}
更新:好吧,请叫ObjectToFileUtil类,粘贴此code到创建的类</ P>
包装&LT; yourpackagehere取代;
进口android.os.Environment;
进口java.io. *;
公共类ObjectToFileUtil {
公共静态字符串objectToFile(Object对象)抛出IOException异常{
字符串路径= Environment.getExternalStorageDirectory()+文件分割符+缓存+文件分割符;
文件DIR =新的文件(路径);
如果(!dir.exists()){
dir.mkdirs();
}
路径+ =数据;
文件数据=新的文件(路径);
如果(!data.createNewFile()){
data.delete();
data.createNewFile();
}
ObjectOutputStream的ObjectOutputStream的=新的ObjectOutputStream(新的FileOutputStream(数据));
objectOutputStream.writeObject(对象);
objectOutputStream.close();
返回路径;
}
公共静态对象objectFromFile(字符串路径)抛出IOException异常,ClassNotFoundException异常{
Object对象= NULL;
文件数据=新的文件(路径);
如果(data.exists()){
ObjectInputStream的ObjectInputStream的=新的ObjectInputStream(新的FileInputStream(数据));
对象= objectInputStream.readObject();
objectInputStream.close();
}
返回对象;
}
}
变化与LT; yourpackagehere>你的包名,不要忘了加上 WRITE_EXTERNAL_STORAGE 许可 AndroidManifest.xml中。在您的MainActivity添加字段
私人字符串数据路径;
和更换JSONAsyncTask类的onPostExecute方法
保护无效onPostExecute(布尔结果){
dialog.cancel();
adapter.notifyDataSetChanged();
如果(结果){
尝试 {
数据路径= objectToFile(ArrayList中);
}赶上(IOException异常E){
e.printStackTrace();
}
} 其他 {
Toast.makeText(getApplicationContext(),无法获取来自服务器的数据,Toast.LENGTH_LONG).show();
}
}
现在您可以访问文件随时得到actorsList使用,当你想,
尝试{
actorsList =(ArrayList的&LT;演员&GT;)objectFromFile(数据路径);
}赶上(IOException异常E){
e.printStackTrace();
}赶上(ClassNotFoundException异常E){
e.printStackTrace();
}
如果你想关闭应用程序,您必须保存数据路径字符串(和负载在应用程序启动),例如后保存文件的路径,使用<一个href="http://stackoverflow.com/questions/3624280/how-to-use-shared$p$pferences-in-android-to-store-fetch-and-edit-values">Shared$p$pferences.
I have parsed JSON successfully but now i want to Cache it for offline usage, even internet is not available, and if any new entry comes i want to cache that as well.
And what would be the best option to cache data ? SharedPreferences
or SQLite database
Here is my code, which i am using to Parse JSON:
public class MainActivity extends Activity {
ArrayList<Actors> actorsList;
ActorAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
actorsList = new ArrayList<Actors>();
new JSONAsyncTask().execute("http://microblogging.wingnity.com/JSONParsingTutorial/jsonActors");
ListView listview = (ListView)findViewById(R.id.list);
adapter = new ActorAdapter(getApplicationContext(), R.layout.row, actorsList);
listview.setAdapter(adapter);
listview.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int position,
long id) {
// TODO Auto-generated method stub
Toast.makeText(getApplicationContext(), actorsList.get(position).getName(), Toast.LENGTH_LONG).show();
}
});
}
class JSONAsyncTask extends AsyncTask<String, Void, Boolean> {
ProgressDialog dialog;
@Override
protected void onPreExecute() {
super.onPreExecute();
dialog = new ProgressDialog(MainActivity.this);
dialog.setMessage("Loading, please wait");
dialog.setTitle("Connecting server");
dialog.show();
dialog.setCancelable(false);
}
@Override
protected Boolean doInBackground(String... urls) {
try {
//------------------>>
HttpGet httppost = new HttpGet(urls[0]);
HttpClient httpclient = new DefaultHttpClient();
HttpResponse response = httpclient.execute(httppost);
// StatusLine stat = response.getStatusLine();
int status = response.getStatusLine().getStatusCode();
if (status == 200) {
HttpEntity entity = response.getEntity();
String data = EntityUtils.toString(entity);
JSONObject jsono = new JSONObject(data);
JSONArray jarray = jsono.getJSONArray("actors");
for (int i = 0; i < jarray.length(); i++) {
JSONObject object = jarray.getJSONObject(i);
Actors actor = new Actors();
actor.setName(object.getString("name"));
actor.setDescription(object.getString("description"));
actorsList.add(actor);
}
return true;
}
//------------------>>
} catch (ParseException e1) {
e1.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (JSONException e) {
e.printStackTrace();
}
return false;
}
protected void onPostExecute(Boolean result) {
dialog.cancel();
adapter.notifyDataSetChanged();
if(result == false)
Toast.makeText(getApplicationContext(), "Unable to fetch data from server", Toast.LENGTH_LONG).show();
}
}
}
Why not just save it to cache folder of your app using something like this:
String path = Environment.getExternalStorageDirectory() + File.separator + "cache" + File.separator;
File dir = new File(path);
if (!dir.exists()) {
dir.mkdirs();
}
path += "data";
File data = new File(path);
if (!data.createNewFile()) {
data.delete();
data.createNewFile();
}
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(data));
objectOutputStream.writeObject(actorsList);
objectOutputStream.close();
And after, you can read it in any time using:
List<?> list = null;
File data = new File(path);
try {
if(data.exists()) {
ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(data));
list = (List<Object>) objectInputStream.readObject();
objectInputStream.close();
}
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
UPDATE: Okay, make class named ObjectToFileUtil, paste this code to created class
package <yourpackagehere>;
import android.os.Environment;
import java.io.*;
public class ObjectToFileUtil {
public static String objectToFile(Object object) throws IOException {
String path = Environment.getExternalStorageDirectory() + File.separator + "cache" + File.separator;
File dir = new File(path);
if (!dir.exists()) {
dir.mkdirs();
}
path += "data";
File data = new File(path);
if (!data.createNewFile()) {
data.delete();
data.createNewFile();
}
ObjectOutputStream objectOutputStream = new ObjectOutputStream(new FileOutputStream(data));
objectOutputStream.writeObject(object);
objectOutputStream.close();
return path;
}
public static Object objectFromFile(String path) throws IOException, ClassNotFoundException {
Object object = null;
File data = new File(path);
if(data.exists()) {
ObjectInputStream objectInputStream = new ObjectInputStream(new FileInputStream(data));
object = objectInputStream.readObject();
objectInputStream.close();
}
return object;
}
}
Change < yourpackagehere > to your package name and don't forget to add WRITE_EXTERNAL_STORAGE permission to AndroidManifest.xml. In your MainActivity add field
private String dataPath;
and replace your onPostExecute method of JSONAsyncTask class to
protected void onPostExecute(Boolean result) {
dialog.cancel();
adapter.notifyDataSetChanged();
if(result) {
try {
dataPath = objectToFile(arrayList);
} catch (IOException e) {
e.printStackTrace();
}
} else {
Toast.makeText(getApplicationContext(), "Unable to fetch data from server", Toast.LENGTH_LONG).show();
}
}
Now you can access get actorsList from File anytime when you want, by using
try {
actorsList = (ArrayList<Actors>)objectFromFile(dataPath);
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
If you want to save path of file after closing application you must save dataPath string (and load on application start), for example, using SharedPreferences.
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