我们写了一些例子来演示怎么使用 OkHttp 解决通用的问题，通过阅读这些例子来学习怎么组织所有的事情。自由复制粘贴这些例子。
Synchronous Get
下载一个文件，打印响应头和响应体转化后的字符串。 对于小的文档 response body 的String()方法是方便且高效的。但是如果 response body 比较到大（>1M）应避免使用String()方法，因为这将把整个文档导入内存。这种情况下，优先吧 response body 作为流使用。
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
Request request = new Request.Builder()
.url("http://publicobject.com/helloworld.txt")
.build();
Response response = client.newCall(request).execute();
if(!response.isSuccessful())
throw new IOException("Unexpected code " + response);
Headers responseHeaders = response.headers();
for(int i = 0; i < responseHeaders.size(); i++){
System.out.println(
responseHeaders.name(i) + ":" + responseHeaders.value(i));
}
System.out.println(response.body().string());
}Asynchronous Get
在工作线程下载文件，在 response 响应时回调。当响应头准备好时调用回调函数。读取 response body 可能阻塞线程。OkHttp 目前没有提供获取 response body 部分内容的 API。
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
Request request = new Request.Builder()
.url("http://publicobject.com/hellowworld.txt")
.build();
client.newCall(request).enqueue(new Callback(){
@Override public void onFailure(Call call, IOException e) {
e.printStackTrace();
}
@Override public void onResponse(Call call, Response response) throws IOException {
if (!response.isSuccessful())
throw new IOException("UnExpected code " + response);
Headers responseHeaders = response.headers();
for (int i = 0, size = resonseHeaders.size(); i < size;i++) {
System.out.println(responseHeaders.name(i) + ":" + responseHeaders.value(i));
}
System.out.println(response.body().string());
}
});
}Accessing Headers
一般 HTTP 头的就像一个Map<String, String>：每个字段对应一个值或空值。但是一些头允许多个值就像 Guava 的Multimap。比如一个 HTTP 的 response 支持多个Vary头。OkHttp 的 API 试图使这些情况的使用更舒服。
当写请求头时使用header(name, value)设置唯一的 name 对应的 value。当一个 name 对应多个 value 时，新的设置的 value 会替换原来的 value。使用addHeader(name, value)添加的头不会覆盖原有的头。
当读取 response 中的一个头时，使用header(name)将返回最后一个 name 的值。一般情况也只有一个。如果没有 value 对应header(name)将返回 null，headers(name)将返回一个当前 name 对应 value 的 list。
要访问所有的头，使用Headers类，这个类支持索引访问。
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
Request request = new Request.Builder()
.url("http://api.github.com.repos/square/okhttp/issues")
.header("User-Agent", "OkHttp Headers,java")
.addHeader("Accept", "application/json; q=0.5")
.addHeader("Accept", "application/vnd.github.v3+json")
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessful())
throw new IOException("Unexcepted code " + response);
System.out.prinln("Server: " + response.header("Server"));
System.out.prinln("Date: " + response.header("Date"));
System.out.prinln("Vary: " + response.headers("Vary"));
}Posting a String
用 HTTP POST 发送请求体到服务器。 这个例子发送了一个 markdown 文件到 web 服务器把 markdown 作为 HTML 展示。当请求体大于 1M 时应该避免使用这个 API 因为它会把请求体全部保存到内存中。
public static final MediaType MEDIA_TYPE_MARKDOWN = MediaType.parse("text/x-markdown; charset=utf-8");
private final OkHttoClient client = new OkHttpClient();
public void run() throws IOException {
String postBody = ""
+ "Release\n"
+ "--------\n"
+ "\n"
+ " * _1.0_ May 6, 2013\n"
+ " * _1.1_ June 15, 2013\n"
+ " * _1.2_ August 11, 2013\n";
Request request = new Request.Builder()
.url("http://api.github.com/markdown/raw")
.post(RequestBody.create(MEDIA_TYPE_MARKDOWN, postBody))
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessful())
throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}Post Streaming
这里我们将请求体作为流提交（POST 方式）。请求体的内容在它开始写的时候生成。这个例子流将直接写入 Okio 的缓冲槽。你编程时可能更倾向于OutputStream, 你可以通过BufferedSink.outputStream()获取。
public static final MediaType MEDIA_TYPE_MARKDOWN =
MediaType.parse("text/x-markdown; cjarset=utf-8");
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
RequestBody requestBody = new RequestBody() {
@Override public MediaType contentType() {
return MEDIA_TYPE_MARKDOWN;
}
@Override public void writeTo(BufferedSink sink) throws IOException {
sink.writeUtf8("Numbers\n");
sink.writeUtf8("-------\n");
for (int i =2; i <= 997; i++) {
sink.writeUtf8(String.format(" * %s=%s\n", i, factor(i)));
}
private String factor(int n) {
for (int i = 2; i < n; i++) {
int x = n / i;
if (x * i == n) return factor(x) + x +" x " +i;
}
return Integer,toString(n);
}
}
};
Response response = client.newCall(request).execute();
if (!response.isSuccessful())
throw new IOException("Unexcepted code " + response);
System.out.println(response.body().string());
}Posting a File
使用文件作为请求体是非常方便的。
public static final MediaType MEDIA_TYPE_MARKDOWN = MediaType.parse("text/x-markdown; charset=utf-8");
private final OkHttoClient client = new OkHttpClient();
public void run() throws IOException {
File file = new File("README.md");
Request request = new Request.Builder()
.url("http://api.github.com/markdown/raw")
.post(RequestBody.create(MEDIA_TYPE_MARKDOWN, file))
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessful())
throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}Posting form parameters
用FormBody.Builder创建请求体是可以的就像 HTML 的<form>标签。键和值将 URL 编码来兼容 HTML 表单。
private final OkHttoClient client = new OkHttpClient();
public void run() throws IOException {
RequestBody formBody = new FormBody.Builder()
.add("search", "Jurassic Park")
.build();
Request request = new Request.Builder()
.url("http://api.github.com/markdown/raw")
.post(formBody）
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessful())
throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}Posting a multipart request
MultipartBody.Builder用于创建复杂的请求体来兼容 HTML 文件上传。复杂请求体的每一部分本事就是一个请求体，能够定义其本身的头。目前，这些头应该描述每一部分的请求体，就像它本身的Content-Disposition。Content-Length和Content-Type头将在可用时自动添加。
private static final String IMGUR_CLIENT_ID = "...";
private static final MediaType MEDIA_TYPE_PNG = MediaType.parse("image/png");
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
//Use the imgur image upload API as document at https://api.imgur.com/endpoints.image
RequestBody requestBody = new MultipartBody.Bulder()
.setType(MultiparBody.FORM)
.addFormDataPart("title", "Square Logo")
.addFormDataPart("image", "logo-square.png",
RequestBody.create(MEDIA_TYPE_PNG, new File("website/static/logo-square.png")))
.build();
Request request = new Request.Builder()
.header("Autorization", "Client-ID" + IMGUR_CLIENT_ID)
.url("https://api.imgur.com/3/image")
.post(requestBody)
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessful())
throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}Parse a JSON Response With Gson
Gson 是一个处理 JSON 字符串与 java 对象转换的好用的 API。这里我们使用 Gson 来解析从 GitHub API 获取的 JSON。
注意ResponseBody.charStream()方法将使用从响应头中获取的Content-Type值作为响应体的解码格式。在没有指定的情况下将使用 utf-8 作为解码格式。
private final OkHttpClient client = new OkHttpClient();
private final Gson gson = new Gson();
public void run() throws Exception {
Request request = new Request.Builder()
.url("https://api.github.com/gists.c2a7c39532239ff261be")
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessful())
throw new IOException("Unexpected code " + response);
Gist gist = gson.fromJson(response.budy.charStream(), Gist.class);
for (Map.Entry<String, GistFile> entry : gist.files.entrySet()) {
System.out.println(entry.getKey());
System.out.println(entry.getValue().content);
}
}
static class Gist {
Map<String, GistFile> files;
}
static class GistFile {
String content;
}Response Caching
使用本地缓存 response 需要提供一个可以读写的缓存路径，和缓存的大小。这个缓存路径应该是私有的，不可信的应用不可以读取缓存的内容！
多个本地缓存使用同一个路径是错误的，大部分的应用都应该调用new OkHttpClient()的同时配置缓存，并且保证在任何地方都是使用的同一个。否则两个缓存会相互影响，污染 response 缓存，甚至使你的程序崩溃。
response 缓存会从的 HTTP 头读取配置。你可以添加一个像Cache-Control: max-stale=3600的请求头，OkHttp 缓存就会遵守。你的服务器通过 response 头配置 response 的缓存时间（就像Cache-Control:max-age=9600）。有些缓存头可以控制缓存的 response，控制一个网络缓存，或者通过可选的 GET 验证控制一个网络的 response。
private final OkHttpClient client;
public CacheResponse(File cahceDirectory) throws Exception {
int cacheSize = 10 * 1024 * 1024; //10MiB
Cache cache = new Cache(cacheDirctory, cacheSize);
client = new OkHttpClient.Builder()
.cache(cache)
.build();
}
public void run() throws Exception {
Reques 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 " + response);
String response1Body = response1.body().string();
System.out.println("Response 1 response: " + response1);
System.out.println("Response 1 cache response: " + response1.cahceResponse());
System.out.println("Response 1 network response: " + response1.networkResponse());
Response response2 = client.newCall(request).execute();
if(!response2.isSuccessful())
throw new IOException("Unexpected code " + response);
String response2Body = response2.body().string();
System.out.println("Response 2 response: " + response2);
System.out.println("Response 2 cache response: " + response1.cahceResponse());
System.out.println("Response 2 network response: " + response2.networkResponse());
System.out.println("Response 2 equals Response 1?:" + response1Body.equals(response2Body));
}通过使用CacheControl.FORCE_NETWORK可以阻止使用本地缓存，CacheControl.FORCE_CACHE可以阻止网络缓存。警告：如果你使用了FORCE_CACHEresponse 需要使用网络，否则 OkHttp 将返回504 Unsatisfiable Requestresponse。 （*注：关于缓存的内容可以参考这里）
Canceling a Call
Call.cancel()可以立刻取消正在进行的 call。如果当前的线程正在写 request 或者读 response 将导致IOException。通过取消不必要的 call 可以节省流量；当你通过导航离开应用时应用的同步或异步 call 都可以被取消。
private final ScheduleExecutorService executor = Executors.newScheduledThreadPool(1);
private final OkHttpClient client = new OkHttpCLient();
public void run () throws Exception {
Request request = new Request.Builder()
.url("http://httpbin.org/delay/2")
.build();
final long startNanos = System.nanoTime();
final Call call = client.newCall(request);
// Scheduler a jod to cancel the call in 1 second.
executor.schedule(new Runnable() {
@Override public void run () {
System.out.printf("%.2f Canceling call.%n", (System.nanoTime() - startNanos) / 1e9f);
call.cancel();
System.out.printf("%.2f Canceling call.%n", (System.nanoTime() - startNanos) / 1e9f);
}
}, 1, TimeUnit.SECONDS);
try {
System.out.prinf("%.2f Canceling call.%n", (System.nanoTime() - startNanos) / 1e9f);
Response response = call.execute();
System.out.prinf("%.2f Canceling call.%S%n", (System.nanoTime() - startNanos) / 1e9f, response);
} catch(IOException e) {
System.out.prinf("%.2f Canceling call.%S%n", (System.nanoTime() - startNanos) / 1e9f, e);
}
}Timeouts
访问超时取消的 call 等同于网络不能访问，网络分区可能引起客户端的连接问题，或者服务器的不可用问题。OkHttp 支持设置连接，读，写的超时。
private final OkHttpClient client;
public ConfigureTimeouts() thows Exception {
client = new OkHttpCLient.Builder()
.connectTimeout(10, TimeUnit.SECONDS)
.writeTimeout(10, TimeUnit.SECONDS)
.readeTimeout(30, TimeUnit.SECONDS)
.build();
}
public void run() throws Exception {
Requets requets = new Request.Builder()
.url("http://httpbin.org.delay/2")
.build();
Response response = client.newCall(request).execute();
System.out.prinln("Response completed: " + response);
}Per-call Configuration
所有的 HTTP 客户端配置依赖于OkHttpClient，包括代理设置，超时，和缓存。当你需要改变某个 call 的配置时，调用OkHttpClient.newBuilder()将返回与源客户端公用 pool，dispatcher,和配置的一个构造者。在下一个例子中，我们创建了一个请求分别具有 500ms 的超时和 3000ms 的超时。
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
Request request = new Request.Builder()
.url("http://httpbin.org/delay/1")
.build();
try{
// Copy to customize Okhttp for this request.
OkHttpClient copy = client.newBuilder()
.readTimeout(500, TimeUnit.MILLISECONDS)
.build();
Response response = copy.newCall(request).execute();
System.out.println("Response 1 succeeded: " response);
}catch (IOException e) {
System.out.println("Response 1 failed: " + e);
}
try{
// Copy to customize Okhttp for this request.
OkHttpClient copy = client.newBuilder()
.readTimeout(3000, TimeUnit.MILLISECONDS)
.build();
Response response = copy.newCall(request).execute();
System.out.println("Response 2 succeeded: " response);
}catch (IOException e) {
System.out.println("Response 2 failed: " + e);
}
}Handling authentication
当一个 request 的返回码是401 Not Authorized时 OkHttp 可以自动重试未授权的 requests。 Authenticator用于提供证书。Authenticator 的实现应该构建一个带有确实认证的 request，在没有认证可用时通过返回 null 来跳过重试。
Response.challenges()方法可以获取授权问题的 scheme 和 realm，Basic 认证可以使用Credentials.basic(username, password)来编码请求头。 (*注：关于认证)
private final OkHttpClient client;
public Authenticate() {
client = new OkHttpClient.Builder()
.authenticator(new Autenticator() {
@Override public Request authenticate(Routr rourte, Response response) throws IOException {
System.out.println("Authenicating for response: " + response);
System.out.println("Challenges: " + response.challenges());
String credential = Credentials.basic("jesse", "password1");
return response.request().newBuilder()
.header("Authorization", crebential)
.build();
}
})
.build();
}
public void run() tthrows Exception {
Request request = new Request.Builder()
.url("http://publicobjetc.com/secrets/hellosecret.txt")
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessfun()) throw new IOException("Unexpected code" + response);
System.out.println(response.body().string());
}通过返回 null 避免认证失败时的多次重试。例如在已经重试的情况下结束重试：
if(credentical.equals(response.request().header("Authorization"))) { return null; // If We already failde with these credentials, don't retry. } 你也可以设置重试的次数：
if (responseCount(response) >= 3) {
return null; // If We've failed 3 times, give up.
}
private int responseCount(Reponse response) {
int result = 1;
while ((response = response.priorResponse()) != null) {
result ++;
}
return result;
}