转载注明出处：简书-十个雨点
通过入门和进阶，完全可以使用OkHttp进行绝大部分工作了，这里再讲两个不太会用到的部分——缓存和验证。
缓存
如果要使用缓存，需要建立一个缓存文件夹，并设置缓存的大小。请注意：
- 这个缓存文件夹不能被外部程序访问。
- 整个程序应该只使用一个缓存，也就是共享一个OkHttpClient实例。
3.通过设置HTTP头来为每个请求配置缓存的使用情况，比如Cache-Control: max-age=9600指定缓存的生存期，Cache-Control:no-cache指定不使用缓存。
示例代码：
private final OkHttpClient client;
public CacheResponse(File cacheDirectory) throws Exception {
int cacheSize = 10 * 1024 * 1024; // 10 MiB
Cache cache = new Cache(cacheDirectory, cacheSize);
client = new OkHttpClient.Builder()
.cache(cache)
.build();
}
public void run() throws Exception {
Request request = new Request.Builder()
.url("http://publicobject.com/helloworld.txt")
.build();
Response response1 = client.newCall(request).execute();
if (!response1.isSuccessful()) throw new IOException("Unexpected code " + response1);
String response1Body = response1.body().string();
System.out.println("Response 1 response: " + response1);
System.out.println("Response 1 cache response: " + response1.cacheResponse());
System.out.println("Response 1 network response: " + response1.networkResponse());
Response response2 = client.newCall(request).execute();
if (!response2.isSuccessful()) throw new IOException("Unexpected code " + response2);
String response2Body = response2.body().string();
System.out.println("Response 2 response: " + response2);
System.out.println("Response 2 cache response: " + response2.cacheResponse());
System.out.println("Response 2 network response: " + response2.networkResponse());
System.out.println("Response 2 equals Response 1? " + response1Body.equals(response2Body));
}
验证
OkHttp会自动重试未验证的请求。当响应是401 Not Authorized时，会要求Authenticator提供证书。Authenticator的实现中需要建立一个包含证书的新请求。如果没有证书可用，返回null来跳过。
示例代码：
private final OkHttpClient client;
public Authenticate() {
client = new OkHttpClient.Builder()
.authenticator(new Authenticator() {
@Override public Request authenticate(Route route, Response response) throws IOException {
System.out.println("Authenticating for response: " + response);
System.out.println("Challenges: " + response.challenges());
String credential = Credentials.basic("jesse", "password1");
return response.request().newBuilder()
.header("Authorization", credential)
.build();
}
})
.build();
}
public void run() throws Exception {
Request request = new Request.Builder()
.url("http://publicobject.com/secrets/hellosecret.txt")
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}
通过返回null，可以避免反复进行多次验证：
if (credential.equals(response.request().header("Authorization"))) {
return null; // If we already failed with these credentials, don't retry.
}
或者在尝试过一定次数以后再放弃尝试：
if (responseCount(response) >= 3) {
return null; // If we've failed 3 times, give up.
}
private int responseCount(Response response) {
int result = 1;
while ((response = response.priorResponse()) != null) {
result++;
}
return result;
}
