Android 设置 Volley 以从缓存中使用 [英] Android set up Volley to use from cache
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问题描述
我正在尝试为服务器 JSON 响应创建和使用缓存.
I'm trying to create and use a cache for a server JSON response.
例如:
将 JSON 对象缓存到内部存储器中，并在我们没有互联网连接时使用它.
cache JSON objects to internal memory and use that when we don't have an internet connection.
在以下示例代码中，我找不到关于如何使用 Volley 缓存它并在再次更新的服务器标头未过期时重新使用它的任何文档.
In the following sample code, I can not find any document about how to cache it with Volley and reuse that when server header for update again don't expire.
像这样:将过期设置为标头并使用缓存并在过期后再次尝试加载.
Like this: set expiration to header and use cache and try to load again after expiration.
我正在尝试为此方法设置缓存机制:
I'm trying to set cache mechanism for this method:
private void makeJsonArryReq() {
JsonArrayRequest req = new JsonArrayRequest(Const.URL_JSON_ARRAY,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
msgResponse.setText(response.toString());
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
});
AppController.getInstance().addToRequestQueue(req,tag_json_arry);
}
缓存方法:
public static Cache.Entry parseIgnoreCacheHeaders(NetworkResponse response) {
long now = System.currentTimeMillis();
Map<String, String> headers = response.headers;
long serverDate = 0;
String serverEtag = null;
String headerValue;
headerValue = headers.get("Date");
if (headerValue != null) {
serverDate = HttpHeaderParser.parseDateAsEpoch(headerValue);
}
serverEtag = headers.get("ETag");
final long cacheHitButRefreshed = 3 * 60 * 1000; // in 3 minutes cache will be hit, but also refreshed on background
final long cacheExpired = 24 * 60 * 60 * 1000; // in 24 hours this cache entry expires completely
final long softExpire = now + cacheHitButRefreshed;
final long ttl = now + cacheExpired;
Cache.Entry entry = new Cache.Entry();
entry.data = response.data;
entry.etag = serverEtag;
entry.softTtl = softExpire;
entry.ttl = ttl;
entry.serverDate = serverDate;
entry.responseHeaders = headers;
return entry;
}
推荐答案
请注意，如果 Web 服务支持缓存输出，则不必使用下面的 CacheRequest，因为 Volley 会自动缓存.
Please note that if the web service supports caching output, you don't have to use CacheRequest below, because Volley will automatically cache.
对于您的问题，我在 parseCacheHeaders 中使用了一些代码(并参考了@oleksandr_yefremov 的代码).下面的代码我已经测试过了.当然，也可以用于JsonArrayRequest.希望这有帮助！
For your issue, I use some codes inside parseCacheHeaders (and refering to @oleksandr_yefremov's codes). The following code I have tested. Of course, can use for JsonArrayRequest also. Hope this help!
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(0, mUrl, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
try {
mTextView.setText(response.toString(5));
} catch (JSONException e) {
mTextView.setText(e.toString());
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
}
}) {
@Override
protected Response<JSONObject> parseNetworkResponse(NetworkResponse response) {
try {
Cache.Entry cacheEntry = HttpHeaderParser.parseCacheHeaders(response);
if (cacheEntry == null) {
cacheEntry = new Cache.Entry();
}
final long cacheHitButRefreshed = 3 * 60 * 1000; // in 3 minutes cache will be hit, but also refreshed on background
final long cacheExpired = 24 * 60 * 60 * 1000; // in 24 hours this cache entry expires completely
long now = System.currentTimeMillis();
final long softExpire = now + cacheHitButRefreshed;
final long ttl = now + cacheExpired;
cacheEntry.data = response.data;
cacheEntry.softTtl = softExpire;
cacheEntry.ttl = ttl;
String headerValue;
headerValue = response.headers.get("Date");
if (headerValue != null) {
cacheEntry.serverDate = HttpHeaderParser.parseDateAsEpoch(headerValue);
}
headerValue = response.headers.get("Last-Modified");
if (headerValue != null) {
cacheEntry.lastModified = HttpHeaderParser.parseDateAsEpoch(headerValue);
}
cacheEntry.responseHeaders = response.headers;
final String jsonString = new String(response.data,
HttpHeaderParser.parseCharset(response.headers));
return Response.success(new JSONObject(jsonString), cacheEntry);
} catch (UnsupportedEncodingException e) {
return Response.error(new ParseError(e));
} catch (JSONException e) {
return Response.error(new ParseError(e));
}
}
@Override
protected void deliverResponse(JSONObject response) {
super.deliverResponse(response);
}
@Override
public void deliverError(VolleyError error) {
super.deliverError(error);
}
@Override
protected VolleyError parseNetworkError(VolleyError volleyError) {
return super.parseNetworkError(volleyError);
}
};
MySingleton.getInstance(this).addToRequestQueue(jsonObjectRequest);
<小时>
更新:
如果需要基类，参考以下代码:
If you want a base class, refer to the following codes:
public class CacheRequest extends Request<NetworkResponse> {
private final Response.Listener<NetworkResponse> mListener;
private final Response.ErrorListener mErrorListener;
public CacheRequest(int method, String url, Response.Listener<NetworkResponse> listener, Response.ErrorListener errorListener) {
super(method, url, errorListener);
this.mListener = listener;
this.mErrorListener = errorListener;
}
@Override
protected Response<NetworkResponse> parseNetworkResponse(NetworkResponse response) {
Cache.Entry cacheEntry = HttpHeaderParser.parseCacheHeaders(response);
if (cacheEntry == null) {
cacheEntry = new Cache.Entry();
}
final long cacheHitButRefreshed = 3 * 60 * 1000; // in 3 minutes cache will be hit, but also refreshed on background
final long cacheExpired = 24 * 60 * 60 * 1000; // in 24 hours this cache entry expires completely
long now = System.currentTimeMillis();
final long softExpire = now + cacheHitButRefreshed;
final long ttl = now + cacheExpired;
cacheEntry.data = response.data;
cacheEntry.softTtl = softExpire;
cacheEntry.ttl = ttl;
String headerValue;
headerValue = response.headers.get("Date");
if (headerValue != null) {
cacheEntry.serverDate = HttpHeaderParser.parseDateAsEpoch(headerValue);
}
headerValue = response.headers.get("Last-Modified");
if (headerValue != null) {
cacheEntry.lastModified = HttpHeaderParser.parseDateAsEpoch(headerValue);
}
cacheEntry.responseHeaders = response.headers;
return Response.success(response, cacheEntry);
}
@Override
protected void deliverResponse(NetworkResponse response) {
mListener.onResponse(response);
}
@Override
protected VolleyError parseNetworkError(VolleyError volleyError) {
return super.parseNetworkError(volleyError);
}
@Override
public void deliverError(VolleyError error) {
mErrorListener.onErrorResponse(error);
}
}
然后在MainActivity中，你可以这样调用
Then in MainActivity, you can call like this
CacheRequest cacheRequest = new CacheRequest(0, mUrl, new Response.Listener<NetworkResponse>() {
@Override
public void onResponse(NetworkResponse response) {
try {
final String jsonString = new String(response.data,
HttpHeaderParser.parseCharset(response.headers));
JSONObject jsonObject = new JSONObject(jsonString);
mTextView.setText(jsonObject.toString(5));
} catch (UnsupportedEncodingException | JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
mTextView.setText(error.toString());
}
});
MySingleton.getInstance(this).addToRequestQueue(cacheRequest);
<小时>
使用完整源代码更新:
MainActivity.java:
MainActivity.java:
package com.example.cachevolley;
import android.content.Context;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.Toast;
import com.android.volley.Cache;
import com.android.volley.NetworkResponse;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.HttpHeaderParser;
import com.android.volley.toolbox.Volley;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.UnsupportedEncodingException;
public class MainActivity extends AppCompatActivity {
private final Context mContext = this;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final TextView textView = (TextView) findViewById(R.id.textView);
RequestQueue queue = Volley.newRequestQueue(this);
String url = "http://192.168.0.100/apitest";
CacheRequest cacheRequest = new CacheRequest(0, url, new Response.Listener<NetworkResponse>() {
@Override
public void onResponse(NetworkResponse response) {
try {
final String jsonString = new String(response.data,
HttpHeaderParser.parseCharset(response.headers));
JSONObject jsonObject = new JSONObject(jsonString);
textView.setText(jsonObject.toString(5));
Toast.makeText(mContext, "onResponse:
" + jsonObject.toString(), Toast.LENGTH_SHORT).show();
} catch (UnsupportedEncodingException | JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(mContext, "onErrorResponse:
" + error.toString(), Toast.LENGTH_SHORT).show();
}
});
// Add the request to the RequestQueue.
queue.add(cacheRequest);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
private class CacheRequest extends Request<NetworkResponse> {
private final Response.Listener<NetworkResponse> mListener;
private final Response.ErrorListener mErrorListener;
public CacheRequest(int method, String url, Response.Listener<NetworkResponse> listener, Response.ErrorListener errorListener) {
super(method, url, errorListener);
this.mListener = listener;
this.mErrorListener = errorListener;
}
@Override
protected Response<NetworkResponse> parseNetworkResponse(NetworkResponse response) {
Cache.Entry cacheEntry = HttpHeaderParser.parseCacheHeaders(response);
if (cacheEntry == null) {
cacheEntry = new Cache.Entry();
}
final long cacheHitButRefreshed = 3 * 60 * 1000; // in 3 minutes cache will be hit, but also refreshed on background
final long cacheExpired = 24 * 60 * 60 * 1000; // in 24 hours this cache entry expires completely
long now = System.currentTimeMillis();
final long softExpire = now + cacheHitButRefreshed;
final long ttl = now + cacheExpired;
cacheEntry.data = response.data;
cacheEntry.softTtl = softExpire;
cacheEntry.ttl = ttl;
String headerValue;
headerValue = response.headers.get("Date");
if (headerValue != null) {
cacheEntry.serverDate = HttpHeaderParser.parseDateAsEpoch(headerValue);
}
headerValue = response.headers.get("Last-Modified");
if (headerValue != null) {
cacheEntry.lastModified = HttpHeaderParser.parseDateAsEpoch(headerValue);
}
cacheEntry.responseHeaders = response.headers;
return Response.success(response, cacheEntry);
}
@Override
protected void deliverResponse(NetworkResponse response) {
mListener.onResponse(response);
}
@Override
protected VolleyError parseNetworkError(VolleyError volleyError) {
return super.parseNetworkError(volleyError);
}
@Override
public void deliverError(VolleyError error) {
mErrorListener.onErrorResponse(error);
}
}
}
清单文件:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.cachevolley" >
<uses-permission android:name="android.permission.INTERNET" />
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
布局文件:
<RelativeLayout 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: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=".MainActivity">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
</RelativeLayout>
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