Volley Session的小结

标签（空格分隔）： Volley Session小结

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Volley创建过程

public static RequestQueue newRequestQueue(Context context, HttpStack stack) {    File cacheDir = new File(context.getCacheDir(), DEFAULT_CACHE_DIR);    String userAgent = "volley/0";    try {        String packageName = context.getPackageName();        PackageInfo info = context.getPackageManager().getPackageInfo(packageName, 0);        userAgent = packageName + "/" + info.versionCode;    } catch (NameNotFoundException e) {    }    if (stack == null) {        if (Build.VERSION.SDK_INT >= 9) {            stack = new HurlStack();        } else {            // Prior to Gingerbread, HttpUrlConnection was unreliable.            // See: http://android-developers.blogspot.com/2011/09/androids-http-clients.html            stack = new HttpClientStack(AndroidHttpClient.newInstance(userAgent));        }    }    Network network = new BasicNetwork(stack);    RequestQueue queue = new RequestQueue(new DiskBasedCache(cacheDir), network);    queue.start();    return queue;}

Volley默认给出了两种创建方式，其中HurlStack对应HttpURLConnection，而HttpClientStack对应于HttpClient.默认情况下，Volley是不支持Cookies和Session的。这两种情况下添加session支持的方式如下。

两种方式对Session支持：
1.HttpURLConnection方式

CookieManager cookieManager = new CookieManager(  );CookieHandler.setDefault( cookieManager );RequestQueue mRequestQueue = Volley.newRequestQueue( context )

添加一个CookieManager即可让HttpURLConnection支持session,在HttpURLConnectionImpl实现类中OkHttpClient会引用这个cookiemanager对象。均为java.net包下提供。这种方式目前没有并发问题，下面来看看另外一种。

2.HttpClient方式

//自定义一个PreferencesCookieStore对象，把cookie值本地化存起来HttpClient defaultHttpClient = new DefaultHttpClient();CookieStore cookieStore = new PreferencesCookieStore( context );defaultHttpClient.setCookieStore( cookieStore );HttpStack httpStack = new HttpClientStack( defaultHttpClient );RequestQueue mRequestQueue = Volley.newRequestQueue( context, httpStack );

但是有一个严重问题使用这种方式之后,网络请求由httpClient执行，我们会失去Volley一个很重要的并发功能，因为我们使用的是HttpClient的一个单例，我们必须遵守它的规则，同一个实例下一个请求必须在上一个请求已经结束情况下才行。很显然，这样使用Volley并发的问题在实际开发中完全不能满足我们的需要。下面是一种改良法，经我测试，只不过是加上的等待机制，对于真正并发来说效率低了许多。
如下：

DefaultHttpClient defaultHttpClient = new DefaultHttpClient();ClientConnectionManager mClientConnectionManager = defaultHttpClient.getConnectionManager();HttpParams mHttpParams = defaultHttpClient.getParams();ThreadSafeClientConnManager mThreadSafeClientConnManager = new ThreadSafeClientConnManager( mHttpParams,       mClientConnectionManager.getSchemeRegistry() );defaultHttpClient = new DefaultHttpClient( mThreadSafeClientConnManager, mHttpParams );CookieStore cookieStore = new PreferencesCookieStore( context );defaultHttpClient.setCookieStore( cookieStore );HttpStack httpStack = new HttpClientStack( defaultHttpClient );mRequestQueue = Volley.newRequestQueue( context, httpStack );

关于HttpClient的Cookie机制简要说明，假设cookie保存在本地，当去请求一个网址的时候，request会获取本地的cookie对象(CookieStore.getCookies())，即是我们代码中setCookieStore设置的，第一次,本地cookie是空，这个时候服务器给回response的时候，会根据规则判断是否要往本地写cookie (CookieStore.addCookie(Cookie))，第一次显然会将当前这次连接的cookie信息保存下来。以后再由请求的时候，即能从本地中获取cookie去请求了，当然整个过程复杂度是比较高的

eg:自定义PreferencesCookieStore如下

PreferencesCookieStore.java

import android.content.Context;import android.content.SharedPreferences;import android.text.TextUtils;import org.apache.http.client.CookieStore;import org.apache.http.cookie.Cookie;import org.apache.http.impl.cookie.BasicClientCookie;import java.io.ByteArrayInputStream;import java.io.ByteArrayOutputStream;import java.io.IOException;import java.io.ObjectInputStream;import java.io.ObjectOutputStream;import java.io.Serializable;import java.util.ArrayList;import java.util.Date;import java.util.List;import java.util.concurrent.ConcurrentHashMap;/** * 保存到 Preferences 的cookie * */public class PreferencesCookieStore implements CookieStore {  private static final String COOKIE_PREFS = "CookiePrefsFile";  private static final String COOKIE_NAME_STORE = "names";  private static final String COOKIE_NAME_PREFIX = "cookie_";  private final ConcurrentHashMap<String, Cookie> cookies;  private final SharedPreferences cookiePrefs;  /**   * Construct a persistent cookie store.   */  public PreferencesCookieStore(Context context) {    cookiePrefs = context.getSharedPreferences(COOKIE_PREFS, 0);    cookies = new ConcurrentHashMap<String, Cookie>();    // Load any previously stored cookies into the store    String storedCookieNames = cookiePrefs.getString(COOKIE_NAME_STORE, null);    if(storedCookieNames != null) {      String[] cookieNames = TextUtils.split(storedCookieNames, ",");      for(String name : cookieNames) {        String encodedCookie = cookiePrefs.getString(COOKIE_NAME_PREFIX + name, null);        if(encodedCookie != null) {          Cookie decodedCookie = decodeCookie(encodedCookie);          if(decodedCookie != null) {            cookies.put(name, decodedCookie);          }        }      }      // Clear out expired cookies      clearExpired(new Date());    }  }  @Override  public void addCookie(Cookie cookie) {    String name = cookie.getName();    // Save cookie into local store, or remove if expired    if(!cookie.isExpired(new Date())) {      cookies.put(name, cookie);    } else {      cookies.remove(name);    }    // Save cookie into persistent store    SharedPreferences.Editor prefsWriter = cookiePrefs.edit();    prefsWriter.putString(COOKIE_NAME_STORE, TextUtils.join(",", cookies.keySet()));    prefsWriter.putString(COOKIE_NAME_PREFIX + name, encodeCookie( new SerializableCookie( cookie ) ));    prefsWriter.commit();  }  @Override  public void clear() {    // Clear cookies from local store    cookies.clear();    // Clear cookies from persistent store    SharedPreferences.Editor prefsWriter = cookiePrefs.edit();    for(String name : cookies.keySet()) {      prefsWriter.remove(COOKIE_NAME_PREFIX + name);    }    prefsWriter.remove(COOKIE_NAME_STORE);    prefsWriter.commit();  }  @Override  public boolean clearExpired(Date date) {    boolean clearedAny = false;    SharedPreferences.Editor prefsWriter = cookiePrefs.edit();    for(ConcurrentHashMap.Entry<String, Cookie> entry : cookies.entrySet()) {      String name = entry.getKey();      Cookie cookie = entry.getValue();      if(cookie.isExpired(date)) {        // 清除cookies        cookies.remove(name);        // Clear cookies from persistent store        prefsWriter.remove(COOKIE_NAME_PREFIX + name);        // We've cleared at least one        clearedAny = true;      }    }    // Update names in persistent store    if(clearedAny) {      prefsWriter.putString(COOKIE_NAME_STORE, TextUtils.join(",", cookies.keySet()));    }    prefsWriter.commit();    return clearedAny;  }  @Override  public List<Cookie> getCookies() {    return new ArrayList<Cookie>(cookies.values());  }  protected String encodeCookie(SerializableCookie cookie) {    ByteArrayOutputStream os = new ByteArrayOutputStream();    try {      ObjectOutputStream outputStream = new ObjectOutputStream(os);      outputStream.writeObject(cookie);    } catch (Exception e) {      return null;    }    return byteArrayToHexString(os.toByteArray());  }  protected Cookie decodeCookie(String cookieStr) {    byte[] bytes = hexStringToByteArray(cookieStr);    ByteArrayInputStream is = new ByteArrayInputStream(bytes);    Cookie cookie = null;    try {      ObjectInputStream ois = new ObjectInputStream(is);      cookie = ((SerializableCookie)ois.readObject()).getCookie();    } catch (Exception e) {      e.printStackTrace();    }    return cookie;  }  // Using some super basic byte array <-> hex conversions so we don't have  // to rely on any large Base64 libraries. Can be overridden if you like!  protected String byteArrayToHexString(byte[] b) {    StringBuffer sb = new StringBuffer(b.length * 2);    for (byte element : b) {      int v = element & 0xff;      if(v < 16) {        sb.append('0');      }      sb.append(Integer.toHexString(v));    }    return sb.toString().toUpperCase();  }  protected byte[] hexStringToByteArray(String s) {    int len = s.length();    byte[] data = new byte[len / 2];    for(int i=0; i<len; i+=2) {      data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4) + Character.digit(s.charAt(i+1), 16));    }    return data;  }  public class SerializableCookie implements Serializable {    private static final long serialVersionUID = 6374381828722046732L;    private transient final Cookie cookie;    private transient BasicClientCookie clientCookie;    public SerializableCookie(Cookie cookie) {      this.cookie = cookie;    }    public Cookie getCookie() {      Cookie bestCookie = cookie;      if(clientCookie != null) {        bestCookie = clientCookie;      }      return bestCookie;    }    private void writeObject(ObjectOutputStream out) throws IOException {      out.writeObject(cookie.getName());      out.writeObject(cookie.getValue());      out.writeObject(cookie.getComment());      out.writeObject(cookie.getDomain());      out.writeObject(cookie.getExpiryDate());      out.writeObject(cookie.getPath());      out.writeInt(cookie.getVersion());      out.writeBoolean(cookie.isSecure());    }    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {      String name = (String)in.readObject();      String value = (String)in.readObject();      clientCookie = new BasicClientCookie(name, value);      clientCookie.setComment((String)in.readObject());      clientCookie.setDomain((String)in.readObject());      clientCookie.setExpiryDate((Date)in.readObject());      clientCookie.setPath((String)in.readObject());      clientCookie.setVersion(in.readInt());      clientCookie.setSecure(in.readBoolean());    }  }}