BasicNetwork详解
BasicNetwork详解
BasicNetwork负责完成网络请求，受NetworkDispatcher类调用。在NetworkDispatcher的run()方法中，是这样调用的。
void run(){
processRequest();
}
......
void processRequest(Request request) {
......
// Perform the network request.
NetworkResponse networkResponse = mNetwork.performRequest(request);
request.addMarker("network-http-complete");
......
}
......
Network
它是接口Network的一个实例。老规矩，我们看看这个类的注释：
/** A network performing Volley requests over an {@link HttpStack}. */
它实现了Network接口。我们阅读一下这个类的源码。
/** An interface for performing requests. */
public interface Network {
/**
* Performs the specified request.
*
* @param request Request to process
* @return A {@link NetworkResponse} with data and caching metadata; will never be null
* @throws VolleyError on errors
*/
NetworkResponse performRequest(Request request) throws VolleyError;
}
注释说明，这个是一个实现请求的接口。只有一个方法-performRequest()。一个入参，泛型Reqest。这个方法的作用是实现指定的请求。返回的是请求的结果为-NetworkResponse。
Request
Request是一个抽象类，所有的请求都是继承于这个，作用就是进行网络请求参数的封装和请求结果的解析。在这里暂时不详细介绍。它有三个重要的方法:
/**
* Subclasses must implement this to parse the raw network response and return an appropriate
* response type. This method will be called from a worker thread. The response will not be
* delivered if you return null.
*
* @param response Response from the network
* @return The parsed response, or null in the case of an error
*/
@Override
protected void deliverResponse(String response);
/**
* Subclasses must implement this to perform delivery of the parsed response to their listeners.
* The given response is guaranteed to be non-null; responses that fail to parse are not
* delivered.
*
* @param response The parsed response returned by {@link
* #parseNetworkResponse(NetworkResponse)}
*/
@Override
@SuppressWarnings("DefaultCharset")
protected Response parseNetworkResponse(NetworkResponse response)
/**
* Mark this request as canceled.
*
* No callback will be delivered as long as either:
*
*
* - This method is called on the same thread as the {@link ResponseDelivery} is running on.
* By default, this is the main thread.
*
- The request subclass being used overrides cancel() and ensures that it does not invoke
* the listener in {@link #deliverResponse} after cancel() has been called in a
* thread-safe manner.
*
*
* There are no guarantees if both of these conditions aren't met.
*/
@Override
public void cancel()
作用如上的注释。
构造函数
/**
* @deprecated Should never have been exposed in the API. This field may be removed in a future
* release of Volley.
*/
@Deprecated protected final HttpStack mHttpStack;
private final BaseHttpStack mBaseHttpStack;
protected final ByteArrayPool mPool;
/**
* @param httpStack HTTP stack to be used
* @deprecated use {@link #BasicNetwork(BaseHttpStack)} instead to avoid depending on Apache
* HTTP. This method may be removed in a future release of Volley.
*/
@Deprecated
public BasicNetwork(HttpStack httpStack) {
// If a pool isn't passed in, then build a small default pool that will give us a lot of
// benefit and not use too much memory.
this(httpStack, new ByteArrayPool(DEFAULT_POOL_SIZE));
}
/**
* @param httpStack HTTP stack to be used
* @param pool a buffer pool that improves GC performance in copy operations
* @deprecated use {@link #BasicNetwork(BaseHttpStack, ByteArrayPool)} instead to avoid
* depending on Apache HTTP. This method may be removed in a future release of Volley.
*/
@Deprecated
public BasicNetwork(HttpStack httpStack, ByteArrayPool pool) {
mHttpStack = httpStack;
mBaseHttpStack = new AdaptedHttpStack(httpStack);
mPool = pool;
}
/** @param httpStack HTTP stack to be used */
public BasicNetwork(BaseHttpStack httpStack) {
// If a pool isn't passed in, then build a small default pool that will give us a lot of
// benefit and not use too much memory.
this(httpStack, new ByteArrayPool(DEFAULT_POOL_SIZE));
}
/**
* @param httpStack HTTP stack to be used
* @param pool a buffer pool that improves GC performance in copy operations
*/
public BasicNetwork(BaseHttpStack httpStack, ByteArrayPool pool) {
mBaseHttpStack = httpStack;
// Populate mHttpStack for backwards compatibility, since it is a protected field. However,
// we won't use it directly here, so clients which don't access it directly won't need to
// depend on Apache HTTP.
mHttpStack = httpStack;
mPool = pool;
}
额，貌似，遇到了问题，我们要看看HttpStack和ByteArrayPool是个啥东西。
HttpStack
代码不长，我们直接贴出来。
/**
* An HTTP stack abstraction.
*
* @deprecated This interface should be avoided as it depends on the deprecated Apache HTTP library.
* Use {@link BaseHttpStack} to avoid this dependency. This class may be removed in a future
* release of Volley.
*/
@Deprecated
public interface HttpStack {
/**
* Performs an HTTP request with the given parameters.
*
* A GET request is sent if request.getPostBody() == null. A POST request is sent otherwise,
* and the Content-Type header is set to request.getPostBodyContentType().
*
* @param request the request to perform
* @param additionalHeaders additional headers to be sent together with {@link
* Request#getHeaders()}
* @return the HTTP response
*/
HttpResponse performRequest(Request request, Map additionalHeaders)
throws IOException, AuthFailureError;
}
它是一个接口，类说明是：一个抽象的Http栈。又说了：应该避免使用此接口，因为它取决于已弃用的Apache HTTP库。 使用{@link BaseHttpStack}来避免这种依赖。 此类可能会在未来的Volley版本中删除。这是，因为，谷歌android5.0之后更换了将HttpClient更换成了HttpURLConnection。关于这部分，我们先暂时分析到这里，稍后我们在后面详细讲讲网络请求的实现。
ByteArrayPool
类说明：
/**
* ByteArrayPool is a source and repository of byte[] objects. Its purpose is to supply
* those buffers to consumers who need to use them for a short period of time and then dispose of
* them. Simply creating and disposing such buffers in the conventional manner can considerable heap
* churn and garbage collection delays on Android, which lacks good management of short-lived heap
* objects. It may be advantageous to trade off some memory in the form of a permanently allocated
* pool of buffers in order to gain heap performance improvements; that is what this class does.
*
* A good candidate user for this class is something like an I/O system that uses large temporary
* byte[] buffers to copy data around. In these use cases, often the consumer wants the
* buffer to be a certain minimum size to ensure good performance (e.g. when copying data chunks off
* of a stream), but doesn't mind if the buffer is larger than the minimum. Taking this into account
* and also to maximize the odds of being able to reuse a recycled buffer, this class is free to
* return buffers larger than the requested size. The caller needs to be able to gracefully deal
* with getting buffers any size over the minimum.
*
*
If there is not a suitably-sized buffer in its recycling pool when a buffer is requested, this
* class will allocate a new buffer and return it.
*
*
This class has no special ownership of buffers it creates; the caller is free to take a buffer
* it receives from this pool, use it permanently, and never return it to the pool; additionally, it
* is not harmful to return to this pool a buffer that was allocated elsewhere, provided there are
* no other lingering references to it.
*
*
This class ensures that the total size of the buffers in its recycling pool never exceeds a
* certain byte limit. When a buffer is returned that would cause the pool to exceed the limit,
* least-recently-used buffers are disposed.
*/
真正的代码不多，主要注释很详细。 大概的意思是它是一个Byte[]池，作用是能够更快速的对byte[]进行操作，节省I/O，减小内存分配和垃圾回收的系统消耗。提供了两个方法：
- public synchronized byte[] getBuf(int len)
如果一个缓冲区在请求的大小中可用，则返回该缓冲区中的缓冲区;如果池中的缓冲区不可用，则返回一个新的缓冲区。 - public synchronized void returnBuf(byte[] buf)
返回池的缓冲区，如果池超过其分配的大小，则丢弃旧的缓冲区。
回到构造函数。有两个被废弃的，我们不分析了。另外的两个的区别是，一个不带ByteArrayPool。我们直接分析复杂的那个。
/** @param httpStack HTTP stack to be used */
public BasicNetwork(BaseHttpStack httpStack) {
// If a pool isn't passed in, then build a small default pool that will give us a lot of
// benefit and not use too much memory.
this(httpStack, new ByteArrayPool(DEFAULT_POOL_SIZE));
}
/**
* @param httpStack HTTP stack to be used
* @param pool a buffer pool that improves GC performance in copy operations
*/
public BasicNetwork(BaseHttpStack httpStack, ByteArrayPool pool) {
mBaseHttpStack = httpStack;
// Populate mHttpStack for backwards compatibility, since it is a protected field. However,
// we won't use it directly here, so clients which don't access it directly won't need to
// depend on Apache HTTP.
//填充mHttpStack以实现向后兼容性，因为它是受保护的字段。 但是，我们不会在这里直接使用它，因此不直接访问它的客户端不需要依赖Apache HTTP。
mHttpStack = httpStack;
mPool = pool;
}
可以知道，现在我们的网络请求都是使用mBaseHttpStack。
然后我们来看看重写的一个方法-performRequest，从名字可以看出来，这个方法用来实现网络请求。代码有点多，额，我也没办法。读吧。
@Override
public NetworkResponse performRequest(Request request) throws VolleyError {
long requestStart = SystemClock.elapsedRealtime();
while (true) {
HttpResponse httpResponse = null;
byte[] responseContents = null;
List responseHeaders = Collections.emptyList();
try {
// Gather headers.
Map additionalRequestHeaders =
getCacheHeaders(request.getCacheEntry());
httpResponse = mBaseHttpStack.executeRequest(request, additionalRequestHeaders);
int statusCode = httpResponse.getStatusCode();
responseHeaders = httpResponse.getHeaders();
// Handle cache validation.
if (statusCode == HttpURLConnection.HTTP_NOT_MODIFIED) {
Entry entry = request.getCacheEntry();
if (entry == null) {
return new NetworkResponse(
HttpURLConnection.HTTP_NOT_MODIFIED,
/* data= */ null,
/* notModified= */ true,
SystemClock.elapsedRealtime() - requestStart,
responseHeaders);
}
// Combine cached and response headers so the response will be complete.
List combinedHeaders = combineHeaders(responseHeaders, entry);
return new NetworkResponse(
HttpURLConnection.HTTP_NOT_MODIFIED,
entry.data,
/* notModified= */ true,
SystemClock.elapsedRealtime() - requestStart,
combinedHeaders);
}
// Some responses such as 204s do not have content. We must check.
InputStream inputStream = httpResponse.getContent();
if (inputStream != null) {
responseContents =
inputStreamToBytes(inputStream, httpResponse.getContentLength());
} else {
// Add 0 byte response as a way of honestly representing a
// no-content request.
responseContents = new byte[0];
}
// if the request is slow, log it.
long requestLifetime = SystemClock.elapsedRealtime() - requestStart;
logSlowRequests(requestLifetime, request, responseContents, statusCode);
if (statusCode < 200 || statusCode > 299) {
throw new IOException();
}
return new NetworkResponse(
statusCode,
responseContents,
/* notModified= */ false,
SystemClock.elapsedRealtime() - requestStart,
responseHeaders);
} catch (SocketTimeoutException e) {
attemptRetryOnException("socket", request, new TimeoutError());
} catch (MalformedURLException e) {
throw new RuntimeException("Bad URL " + request.getUrl(), e);
} catch (IOException e) {
int statusCode;
if (httpResponse != null) {
statusCode = httpResponse.getStatusCode();
} else {
throw new NoConnectionError(e);
}
VolleyLog.e("Unexpected response code %d for %s", statusCode, request.getUrl());
NetworkResponse networkResponse;
if (responseContents != null) {
networkResponse =
new NetworkResponse(
statusCode,
responseContents,
/* notModified= */ false,
SystemClock.elapsedRealtime() - requestStart,
responseHeaders);
if (statusCode == HttpURLConnection.HTTP_UNAUTHORIZED
|| statusCode == HttpURLConnection.HTTP_FORBIDDEN) {
attemptRetryOnException(
"auth", request, new AuthFailureError(networkResponse));
} else if (statusCode >= 400 && statusCode <= 499) {
// Don't retry other client errors.
throw new ClientError(networkResponse);
} else if (statusCode >= 500 && statusCode <= 599) {
if (request.shouldRetryServerErrors()) {
attemptRetryOnException(
"server", request, new ServerError(networkResponse));
} else {
throw new ServerError(networkResponse);
}
} else {
// 3xx? No reason to retry.
throw new ServerError(networkResponse);
}
} else {
attemptRetryOnException("network", request, new NetworkError());
}
}
}
}
/** Logs requests that took over SLOW_REQUEST_THRESHOLD_MS to complete. */
private void logSlowRequests(
long requestLifetime, Request request, byte[] responseContents, int statusCode) {
if (DEBUG || requestLifetime > SLOW_REQUEST_THRESHOLD_MS) {
VolleyLog.d(
"HTTP response for request=<%s> [lifetime=%d], [size=%s], "
+ "[rc=%d], [retryCount=%s]",
request,
requestLifetime,
responseContents != null ? responseContents.length : "null",
statusCode,
request.getRetryPolicy().getCurrentRetryCount());
}
}
/**
* Attempts to prepare the request for a retry. If there are no more attempts remaining in the
* request's retry policy, a timeout exception is thrown.
*
* @param request The request to use.
*/
private static void attemptRetryOnException(
String logPrefix, Request request, VolleyError exception) throws VolleyError {
RetryPolicy retryPolicy = request.getRetryPolicy();
int oldTimeout = request.getTimeoutMs();
try {
retryPolicy.retry(exception);
} catch (VolleyError e) {
request.addMarker(
String.format("%s-timeout-giveup [timeout=%s]", logPrefix, oldTimeout));
throw e;
}
request.addMarker(String.format("%s-retry [timeout=%s]", logPrefix, oldTimeout));
}
private Map getCacheHeaders(Cache.Entry entry) {
// If there's no cache entry, we're done.
if (entry == null) {
return Collections.emptyMap();
}
Map headers = new HashMap<>();
if (entry.etag != null) {
headers.put("If-None-Match", entry.etag);
}
if (entry.lastModified > 0) {
headers.put(
"If-Modified-Since", HttpHeaderParser.formatEpochAsRfc1123(entry.lastModified));
}
return headers;
}
protected void logError(String what, String url, long start) {
long now = SystemClock.elapsedRealtime();
VolleyLog.v("HTTP ERROR(%s) %d ms to fetch %s", what, (now - start), url);
}
/** Reads the contents of an InputStream into a byte[]. */
private byte[] inputStreamToBytes(InputStream in, int contentLength)
throws IOException, ServerError {
PoolingByteArrayOutputStream bytes = new PoolingByteArrayOutputStream(mPool, contentLength);
byte[] buffer = null;
try {
if (in == null) {
throw new ServerError();
}
buffer = mPool.getBuf(1024);
int count;
while ((count = in.read(buffer)) != -1) {
bytes.write(buffer, 0, count);
}
return bytes.toByteArray();
} finally {
try {
// Close the InputStream and release the resources by "consuming the content".
if (in != null) {
in.close();
}
} catch (IOException e) {
// This can happen if there was an exception above that left the stream in
// an invalid state.
VolleyLog.v("Error occurred when closing InputStream");
}
mPool.returnBuf(buffer);
bytes.close();
}
}
/**
* Converts Headers[] to Map<String, String>.
*
* @deprecated Should never have been exposed in the API. This method may be removed in a future
* release of Volley.
*/
@Deprecated
protected static Map convertHeaders(Header[] headers) {
Map result = new TreeMap<>(String.CASE_INSENSITIVE_ORDER);
for (int i = 0; i < headers.length; i++) {
result.put(headers[i].getName(), headers[i].getValue());
}
return result;
}
/**
* Combine cache headers with network response headers for an HTTP 304 response.
*
* An HTTP 304 response does not have all header fields. We have to use the header fields
* from the cache entry plus the new ones from the response. See also:
* http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.5
*
* @param responseHeaders Headers from the network response.
* @param entry The cached response.
* @return The combined list of headers.
*/
private static List combineHeaders(List responseHeaders, Entry entry) {
// First, create a case-insensitive set of header names from the network
// response.
Set headerNamesFromNetworkResponse = new TreeSet<>(String.CASE_INSENSITIVE_ORDER);
if (!responseHeaders.isEmpty()) {
for (Header header : responseHeaders) {
headerNamesFromNetworkResponse.add(header.getName());
}
}
// Second, add headers from the cache entry to the network response as long as
// they didn't appear in the network response, which should take precedence.
List combinedHeaders = new ArrayList<>(responseHeaders);
if (entry.allResponseHeaders != null) {
if (!entry.allResponseHeaders.isEmpty()) {
for (Header header : entry.allResponseHeaders) {
if (!headerNamesFromNetworkResponse.contains(header.getName())) {
combinedHeaders.add(header);
}
}
}
} else {
// Legacy caches only have entry.responseHeaders.
if (!entry.responseHeaders.isEmpty()) {
for (Map.Entry header : entry.responseHeaders.entrySet()) {
if (!headerNamesFromNetworkResponse.contains(header.getKey())) {
combinedHeaders.add(new Header(header.getKey(), header.getValue()));
}
}
}
}
return combinedHeaders;
}
首先，调用mBaseHttpStack的excuteRequest()方法，得到请求的结果。然后根据响应码，判断是不是304(HttpURLConnection.HTTP_NOT_MODIFIED)，如果是，表明使用上一次请求的结果即可。取request中的cacheEntry的值，创建NetworkResponse，并返回。如果不是，读取接下来的数据流。用 inputStreamToBytes() 方法将接下来的数据流转换成byte[]（注释：就是在这里，我们使用到了byteArrayPool）。
继续判断状态码，如果是小于200或大于299，则表明出现异常了，直接抛出一个IOException异常。在异常catch代码中，我们创建一个异常的NetworkResponse。如果不是，继续往下走。我们根据状态码和内容，创建一个新的NetworkResponse，并返回。好了，BaseNetwork源码就分析完毕。