Android 设置 Volley 以从缓存中使用

Question

我正在尝试为服务器 JSON 响应创建和使用缓存。

例如：

将 JSON 对象缓存到内存中，并在我们没有互联网连接时使用它。

在下面的示例代码中，我找不到任何关于如何使用Volley 缓存它并在再次更新的服务器标头未过期时重用它的文档。

像这样：将过期设置为标头并使用缓存并尝试在过期后再次加载。

我正在尝试为此方法设置缓存机制：

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;
}

Answer 1

请注意，如果网络服务支持缓存输出，则不必使用下面的CacheRequest，因为Volley会自动缓存。

---

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）。以下代码我已经测试过了。当然，也可以用于JsonArrayRequest。希望对您有所帮助！

    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);

---

更新：

如果要基类，参考以下代码：

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，可以这样调用

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);

---

使用完整源代码更新：

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:\n\n" + 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:\n\n" + 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>

Answer 2

如果响应是使用字符串请求从服务器获取的，那么只需替换行

return Response.success(new JSONObject(jsonString), cacheEntry);

有了这个

return Response.success(new String(jsonString), cacheEntry);

它适用于我的情况。试试你自己的代码。