OkHttp 默認是不進行緩存的，需要手動配置
public class OkHttpManager {
private OkHttpClient client;
private OkHttpManager() {
// 緩存目錄
File file = new File(Environment.getExternalStorageDirectory(), "a_cache");
// 緩存大小
int cacheSize = 10 * 1024 * 1024;
client = new OkHttpClient.Builder()
.cache(new Cache(file, cacheSize)) // 配置緩存
.build();
}
public static OkHttpManager getInstance() {
return OkHttpHolder.instance;
}
private static class OkHttpHolder {
private static final OkHttpManager instance = new OkHttpManager();
}
OkHttp使用CacheControl進行緩存控制，這就意味着同時支持Respone緩存和Request緩存控制
Respose
@Override
public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
Response originResponse = chain.proceed(request);
//設置響應的緩存時間爲60秒，即設置Cache-Control頭，並移除pragma消息頭，因爲pragma也是控制緩存的一個消息頭屬性
originResponse = originResponse.newBuilder()
.removeHeader("pragma")
.header("Cache-Control", "max-age=60")
.build();
return originResponse;
}Request
CacheControl cacheControl = new CacheControl.Builder()
.maxStale(10, TimeUnit.SECONDS)
.maxAge(10, TimeUnit.SECONDS)
.build();
Request request = new Request.Builder()
.url("http://publicobject.com/helloworld.txt")
.cacheControl(cacheControl)
.build();
具體實現原理如下
public final class CacheInterceptor implements Interceptor {
final InternalCache cache;
public CacheInterceptor(InternalCache cache) {
this.cache = cache;
}
@Override public Response intercept(Chain chain) throws IOException {
Response cacheCandidate = cache != null
? cache.get(chain.request())
: null;
long now = System.currentTimeMillis();
CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
Request networkRequest = strategy.networkRequest;
Response cacheResponse = strategy.cacheResponse;
if (cache != null) {
cache.trackResponse(strategy);
}
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.
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.
if (networkRequest == null) {
return cacheResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.build();
}
Response networkResponse = null;
try {
networkResponse = chain.proceed(networkRequest);
} finally {
// If we're crashing on I/O or otherwise, don't leak the cache body.
if (networkResponse == null && cacheCandidate != null) {
closeQuietly(cacheCandidate.body());
}
}
// If we have a cache response too, then we're doing a conditional get.
if (cacheResponse != null) {
if (networkResponse.code() == HTTP_NOT_MODIFIED) {
Response response = cacheResponse.newBuilder()
.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());
}
}
Response response = networkResponse.newBuilder()
.cacheResponse(stripBody(cacheResponse))
.networkResponse(stripBody(networkResponse))
.build();
if (cache != null) {
if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
// Offer this request to the cache.
CacheRequest cacheRequest = cache.put(response);
return cacheWritingResponse(cacheRequest, response);
}
if (HttpMethod.invalidatesCache(networkRequest.method())) {
try {
cache.remove(networkRequest);
} catch (IOException ignored) {
// The cache cannot be written.
}
}
}
return response;
}
private static Response stripBody(Response response) {
return response != null && response.body() != null
? response.newBuilder().body(null).build()
: response;
}
/**
* Returns a new source that writes bytes to {@code cacheRequest} as they are read by the source
* consumer. This is careful to discard bytes left over when the stream is closed; otherwise we
* may never exhaust the source stream and therefore not complete the cached response.
*/
private Response cacheWritingResponse(final CacheRequest cacheRequest, Response response)
throws IOException {
// Some apps return a null body; for compatibility we treat that like a null cache request.
if (cacheRequest == null) return response;
Sink cacheBodyUnbuffered = cacheRequest.body();
if (cacheBodyUnbuffered == null) return response;
final BufferedSource source = response.body().source();
final BufferedSink cacheBody = Okio.buffer(cacheBodyUnbuffered);
Source cacheWritingSource = new Source() {
boolean cacheRequestClosed;
@Override public long read(Buffer sink, long byteCount) throws IOException {
long bytesRead;
try {
bytesRead = source.read(sink, byteCount);
} catch (IOException e) {
if (!cacheRequestClosed) {
cacheRequestClosed = true;
cacheRequest.abort(); // Failed to write a complete cache response.
}
throw e;
}
if (bytesRead == -1) {
if (!cacheRequestClosed) {
cacheRequestClosed = true;
cacheBody.close(); // The cache response is complete!
}
return -1;
}
sink.copyTo(cacheBody.buffer(), sink.size() - bytesRead, bytesRead);
cacheBody.emitCompleteSegments();
return bytesRead;
}
@Override public Timeout timeout() {
return source.timeout();
}
@Override public void close() throws IOException {
if (!cacheRequestClosed
&& !discard(this, HttpCodec.DISCARD_STREAM_TIMEOUT_MILLIS, MILLISECONDS)) {
cacheRequestClosed = true;
cacheRequest.abort();
}
source.close();
}
};
String contentType = response.header("Content-Type");
long contentLength = response.body().contentLength();
return response.newBuilder()
.body(new RealResponseBody(contentType, contentLength, Okio.buffer(cacheWritingSource)))
.build();
}
/** Combines cached headers with a network headers as defined by RFC 7234, 4.3.4. */
private static Headers combine(Headers cachedHeaders, Headers networkHeaders) {
Headers.Builder result = new Headers.Builder();
for (int i = 0, size = cachedHeaders.size(); i < size; i++) {
String fieldName = cachedHeaders.name(i);
String value = cachedHeaders.value(i);
if ("Warning".equalsIgnoreCase(fieldName) && value.startsWith("1")) {
continue; // Drop 100-level freshness warnings.
}
if (isContentSpecificHeader(fieldName) || !isEndToEnd(fieldName)
|| networkHeaders.get(fieldName) == null) {
Internal.instance.addLenient(result, fieldName, value);
}
}
for (int i = 0, size = networkHeaders.size(); i < size; i++) {
String fieldName = networkHeaders.name(i);
if (!isContentSpecificHeader(fieldName) && isEndToEnd(fieldName)) {
Internal.instance.addLenient(result, fieldName, networkHeaders.value(i));
}
}
return result.build();
}
/**
* Returns true if {@code fieldName} is an end-to-end HTTP header, as defined by RFC 2616,
* 13.5.1.
*/
static boolean isEndToEnd(String fieldName) {
return !"Connection".equalsIgnoreCase(fieldName)
&& !"Keep-Alive".equalsIgnoreCase(fieldName)
&& !"Proxy-Authenticate".equalsIgnoreCase(fieldName)
&& !"Proxy-Authorization".equalsIgnoreCase(fieldName)
&& !"TE".equalsIgnoreCase(fieldName)
&& !"Trailers".equalsIgnoreCase(fieldName)
&& !"Transfer-Encoding".equalsIgnoreCase(fieldName)
&& !"Upgrade".equalsIgnoreCase(fieldName);
}
/**
* Returns true if {@code fieldName} is content specific and therefore should always be used
* from cached headers.
*/
static boolean isContentSpecificHeader(String fieldName) {
return "Content-Length".equalsIgnoreCase(fieldName)
|| "Content-Encoding".equalsIgnoreCase(fieldName)
|| "Content-Type".equalsIgnoreCase(fieldName);
}
}