OkHttp的橋攔截器的源碼解讀傳送門：http://www.lxweimin.com/p/20bfab62c3cd
OkHttp有自己的一套緩存，其實最終還是使用DiskLruCache進行緩存，通過Okhttp內部的線程池對緩存進行保存清除等操作的。
/** Serves requests from the cache and writes responses to the cache.
*
* 服務來自緩存的請求并將響應寫入緩存
*/
public final class CacheInterceptor implements Interceptor {
final InternalCache cache;
public CacheInterceptor(InternalCache cache) {
this.cache = cache;
}
@Override public Response intercept(Chain chain) throws IOException {
// 讀取候選緩存
Response cacheCandidate = cache != null
? cache.get(chain.request())
: null;
long now = System.currentTimeMillis();
// 緩存策略 可以設置從緩存中取，也可以設置從網絡取，也可以同時設置兩者都使用
CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
Request networkRequest = strategy.networkRequest;
Response cacheResponse = strategy.cacheResponse;
if (cache != null) {
cache.trackResponse(strategy); // 更新緩存策略
}
if (cacheCandidate != null && cacheResponse == null) {
closeQuietly(cacheCandidate.body()); // The cache candidate wasn't applicable. Close it.
}
// If we're forbidden from using the network and the cache is insufficient, fail.
// 當前不能使用網絡，也沒有找到相應的緩存，這時候會構造出一個Response，拋出一個504異常
if (networkRequest == null && cacheResponse == null) {
return new Response.Builder()
.request(chain.request())
.protocol(Protocol.HTTP_1_1)
.code(504)
.message("Unsatisfiable Request (only-if-cached)")
.body(Util.EMPTY_RESPONSE)
.sentRequestAtMillis(-1L)
.receivedResponseAtMillis(System.currentTimeMillis())
.build();
}
// If we don't need the network, we're done.
// 有緩存，不能使用網絡，直接返回緩存的結果
if (networkRequest == null) {
return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
}
Response networkResponse = null;
try {
// 通過調用攔截器的方法進行網絡請求獲取，具體的網絡工作交給下一個攔截器來做的,下一個攔截器其實就是ConnectInterceptor
networkResponse = chain.proceed(networkRequest);
} finally {
// If we're crashing on I/O or otherwise, don't leak the cache body.
// 關閉資源
if (networkResponse == null && cacheCandidate != null) {
closeQuietly(cacheCandidate.body());
}
}
// If we have a cache response too, then we're doing a conditional get.
// 接收到網絡結果，如果響應code式304，則使用緩存，返回緩存結果
if (cacheResponse != null) {
if (networkResponse.code() == HTTP_NOT_MODIFIED) { // 返回的code為304時，表示得從緩存中獲取
.headers(combine(cacheResponse.headers(), networkResponse.headers()))
.sentRequestAtMillis(networkResponse.sentRequestAtMillis())
.receivedResponseAtMillis(networkResponse.receivedResponseAtMillis())
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
networkResponse.body().close();
// Update the cache after combining headers but before stripping the
// Content-Encoding header (as performed by initContentStream()).
cache.trackConditionalCacheHit();
cache.update(cacheResponse, response);
return response;
} else {
closeQuietly(cacheResponse.body());
}
}
// 讀取網絡結果
Response response = networkResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
if (cache != null) {
// 響應頭里面有相應體，緩存策略是可以被緩存的
if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
// Offer this request to the cache. 滿足上面的條件，寫入緩存
CacheRequest cacheRequest = cache.put(response);
return cacheWritingResponse(cacheRequest, response);
}
// 判斷是否是一個無效的緩存方法
if (HttpMethod.invalidatesCache(networkRequest.method())) {
try {
cache.remove(networkRequest);
} catch (IOException ignored) {
// The cache cannot be written.
}
}
}
return response;
}
緩存的存取都是在這個類Cache中操作的：
Cache緩存請求數據和響應數據，通過內部類CacheRequestImpl來實現CacheInterceptor緩存攔截器的緩存的寫入讀取操作。
get方法：
/**
* 獲取響應體數據的方法
* @param request
* @return
*/
@Nullable Response get(Request request) {
String key = key(request.url());
// 最終還是使用DiskLruCache進行緩存，通過Okhttp內部的線程池對緩存進行保存清除等操作的
DiskLruCache.Snapshot snapshot;
Entry entry;
try {
snapshot = cache.get(key);
if (snapshot == null) {
return null;
}
} catch (IOException e) {
// Give up because the cache cannot be read.
return null;
}
try {
entry = new Entry(snapshot.getSource(ENTRY_METADATA));
} catch (IOException e) {
Util.closeQuietly(snapshot);
return null;
}
Response response = entry.response(snapshot);
if (!entry.matches(request, response)) {
Util.closeQuietly(response.body());
return null;
}
return response;
}
涉及到的key方法：
// 對請求的url進行md5處理，并進行16進制轉換
public static String key(HttpUrl url) {
return ByteString.encodeUtf8(url.toString()).md5().hex();
}
put方法：
/**
* 緩存存入數據的方法
* @param response
* @return
*/
@Nullable CacheRequest put(Response response) {
String requestMethod = response.request().method();
if (HttpMethod.invalidatesCache(response.request().method())) {
try {
remove(response.request());
} catch (IOException ignored) {
// The cache cannot be written.
}
return null;
}
if (!requestMethod.equals("GET")) { // Get請求
// Don't cache non-GET responses. We're technically allowed to cache
// HEAD requests and some POST requests, but the complexity of doing
// so is high and the benefit is low.
return null;
}
if (HttpHeaders.hasVaryAll(response)) {
return null;
}
// 需要緩存的實體，這里面封裝了所需要緩存的所有內容
Entry entry = new Entry(response);
DiskLruCache.Editor editor = null;
try {
editor = cache.edit(key(response.request().url()));
if (editor == null) {
return null;
}
entry.writeTo(editor); // 開始真正緩存
return new CacheRequestImpl(editor); // 通過這個接口來實現緩存攔截器的緩存的寫入都去操作
} catch (IOException e) {
abortQuietly(editor);
return null;
}
}
謝謝閱讀，如有錯誤，歡迎指正。
OkHttp的ConnectInterceptor連接攔截器剖析：http://www.lxweimin.com/p/f90aa5894cdf
