OKHTTP 的使用完全解析
一、前言
在Android客户端开发中，使用网络请求是非常常见的事情，一般我们使用HttpURLConnection是可以满足需求的，不过随着业务逻辑复杂，依然还是有很多不便，一个神奇的公司square开源了一个网络请求库——Okhttp。随着Okhttp越来越火，越来越多的人使用Okhttp+retrofit+Rxjava,我们还是很有必要了解一下。本文的实力代码来自官方wiki。
二、下载配置
现在最新的版本是3.X，android支持2.3+，java应用程序中使用，java最低版本是1.7。
可以通过下载jar包获取，也可以通过Maven获取:
<dependency>
<groupId>com.squareup.okhttp3groupId>
<artifactId>okhttpartifactId>
<version>3.4.1version>
dependency>或者Gradle
compile 'com.squareup.okhttp3:okhttp:3.4.1'三、基础使用
- Synchronous (同步的) Get
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());
} OkHttpClient 创建一个请求对象，我们可以通过这个配置缓存、超时目录、代理、拦截器等，大多数时候我们只应该创建一个对象，所有的请求可以共用缓存、连接池、 `拦截器等，如下所示：
OkHttpClient client = new OkHttpClient.Builder()
.readTimeout(8000, TimeUnit.SECONDS)
.connectTimeout(8000, TimeUnit.SECONDS)
.writeTimeout(8000, TimeUnit.SECONDS)
.addInterceptor(new Interceptor())
.cache(cache)
.build();Requests 请求，每个HTTP请求包含一个URL、一个方法(如GET或POST),同时包含头信息的列表。请求也可能包含一个实体:具体类型内容的数据流。
Responses 响应，根据请求返回的响应码(成功的200或没有找到内容的404),头信息,和可选的实体。
Calls 代表一个实际的http请求，一般调用会执行两种方式中的一种:
- 同步:执行execute()方法，你的线程被锁住直到响应返回.
- 异步：执行enqueue()方法，你在任何线程安排请求,在另一个线程获得响应回调，不会阻塞当前线程，通过Callback 对象的成功和失败方法获取响应。
以上代码运行返回如图所示，上面几行是响应头信息，我们可以通过Resbonse的response.headers() 的到Headers对象，我们可以通过索引遍历获取响应头的信息和值，我们不通过遍历也可以通过responseHeaders.get("Cache-Control"); 获取，如果响应头一样，有多个值返回，我们可以通过`public List values(String name) {} 返回一个集合，如果通过Header对象的get方法获取只会返回最后一个数据。
下面返回的就是获得响应体对象response.body() ，调用string() 方法将其转成string对象，对小文件来说string()方法响应实体是方便和高效的.但如果响应实体很大(大于1 MiB),避免使用string(),因为它会将整个文档加载到内存中.在这种情况下,更倾向于用流处理实体。 `
- Asynchronous(异步) Get
代码如下所示：
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
Request request = new Request.Builder()
.url("http://publicobject.com/helloworld.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 = responseHeaders.size(); i < size; i++) {
System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
}
System.out.println(response.body().string());
}
});
} 以上代码异步执行，不会阻塞当前线程，该方法接受一个okhttp3.callback对象，当请求成功后执行callback对象的onResponse方法，我们通过调用isSuccessful() 可以判断返回的响应码是否在200和300之间。当请求失败或取消的会调用callback对象的onFailure 。回调的方法都是执行在工作线程的，不可以直接更新UI。
- Accessing Headers 访问头信息
典型的HTTP头信息的工作像一个Map每个字段都有一个值或没有。但是一些头信息允许多个值,如 Guava’s Multimap.例如,一个HTTP响应提供多个不同的头信息是合法和常见的。OkHttp’s APIs试图使这两种情况下都方便使用，当写请求头信息时,使用header(name, value)为value设置唯一的name。如果values已经存在,他们将被删除然后添加的新value。使用addHeader(name, value)来添加一个新的头信息而不需要移除已经存在的头信息。如下所示：
Request request = new Request.Builder()
.url("https://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();- Posting a String 上传字符串
代码如下所示
public static final MediaType MEDIA_TYPE_MARKDOWN
= MediaType.parse("text/x-markdown; charset=utf-8");
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
String postBody = ""
+ "Releases\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("https://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方发接收一个RequestBody 对象，使用一个HTTP POST发送请求实体到服务.这个例子提交一个markdown文档发送给web服务,将markdown呈现为HTML.因为整个请求实体同时在内存中,避免使用这个API发布大文档(大于1 MiB).
- Post 提交键值对
其实提交键值对跟上传表格参数差不多，我们一般都是一个Map集合传递近来就是了，不用每次都要一个一个add，如下所示：
private final OkHttpClient client = new OkHttpClient();
public void run(Map<String, String> params) throws Exception{
FormBody.Builder builder = new FormBody.Builder();
for (Map.Entry<String, String> entry : params.entrySet()){
builder.add(entry.getKey(),entry.getValue().toString());
}
RequestBody formBody = builder.build();
Request request = new Request.Builder()
.url("https://en.wikipedia.org/w/index.php")
.post(formBody)
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}- Post 提交json
public static final MediaType JSON
= MediaType.parse("application/json; charset=utf-8");
OkHttpClient client = new OkHttpClient();
String post(String url, String json) throws IOException {
RequestBody body = RequestBody.create(JSON, json);
Request request = new Request.Builder()
.url(url)
.post(body)
.build();
Response response = client.newCall(request).execute();
return response.body().string();
}- Post Streaming 上传流
这里我们发布一个请求实体作为一个流. 这个请求实体被写的时候它的内容就产生了.这个例子的流直接进入到 Okio 缓冲池.你的项目可能更喜欢一个OutputStream,你可以从BufferedSink.outputStream()获取.
public static final MediaType MEDIA_TYPE_MARKDOWN
= MediaType.parse("text/x-markdown; charset=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) + " × " + i;
}
return Integer.toString(n);
}
};
Request request = new Request.Builder()
.url("https://api.github.com/markdown/raw")
.post(requestBody)
.build();
Response response = client.newCall(request).execute();
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}- Posting a File 上传文件
很容易使用一个文件作为请求实体.
public static final MediaType MEDIA_TYPE_MARKDOWN
= MediaType.parse("text/x-markdown; charset=utf-8");
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
File file = new File("README.md");
Request request = new Request.Builder()
.url("https://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 上传表格参数
使用FormBody.Builder构建的请求实体，工作起来就像一个HTML 标签。名称和值将使用一种 HTML-compatible 的URL编码。
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
RequestBody formBody = new FormBody.Builder()
.add("search", "Jurassic Park")
.build();
Request request = new Request.Builder()
.url("https://en.wikipedia.org/w/index.php")
.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 上传多部分的请求
MultipartBody.Builder 可以构建兼容HTML文件上传表单的复杂的请求实体。一个多部分请求的每个部分本身就是一个请求实体,并可以定义自己的头信息。如果存在的话,这些头信息应该描述该部分实体,比如它的内容目录.内容长度和内容类型的头信息如果可用的话会自动添加。
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 documented at https://api.imgur.com/endpoints/image
RequestBody requestBody = new MultipartBody.Builder()
.setType(MultipartBody.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("Authorization", "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());
} 设置setType 我们一般将该值设置为MultipartBody.FORM ，addFormDataPart(String name, String value) 我们可以向里面添加键值对，addFormDataPart(String name, String filename, RequestBody body) 我们可以向里面添加文件，addPart 提供了三个重载方法，我们可以通过addPart(Headers headers, RequestBody body)可以在添加RequestBody的时候，同时为其单独设置请求头。如下所示：
RequestBody requestBody = new MultipartBuilder()
.type(MultipartBuilder.FORM)
.addPart(Headers.of("Content-Disposition",
"form-data; name=\"username\""),
RequestBody.create(null, "test"))
.build();- Parse a JSON Response With Gson 用Gson解析一个JSON响应
Gson 是一个方便JSON和Java对象之间互相转换的API.这里我们用它来解析一个来自GitHub API的JSON响应.
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.body().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;
}上面就是通过Gson解析返回的数据，跟平时用法差不多。
- Response Caching 响应缓存
缓存平时我们用的还是挺多的，下面示例代码演示：
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));
} 为了缓存响应,你需要一个缓存目录,你可以读和写,并限制缓存的大小。缓存目录应该是私有的,不受信任的应用程序不应该能够阅读其内容，所以我们一般这样配置，缓存的数据存放在context.getCacheDir()的子目录中:：
final @Nullable File baseDir = context.getCacheDir();
if (baseDir != null) {
final File cacheDir = new File(baseDir, "HttpResponseCache");
okHttpClient.setCache(new Cache(cacheDir, 10 * 10 * 1024));
} 第一次请求完成后，Okhttp将请求结果写入了缓存当中，第一次response1.networkResponse()为请求的值，response1.cacheResponse() 打印的值为null；第二次response2.cacheResponse() 打印的是第一次网络请求的值，response2.networkResponse() 打印的值是null，说明你第一次走的网络请求，第二次请求来自于缓存，两次的值response1Body.equals(response2Body) 返回也是true，很好的验证上面的说法。我们还可以配置响应头信息Cache-Control:max-stale=3600 Cache-Control: max-age=9600 ,okhttp也会对配置进行缓存处理，超过时间走网络请求。禁止一个响应使用缓存,只获取网络响应,使用CacheControl.FORCE_NETWORK。禁止一个响应使用网络,只使用缓存,使用CacheControl.FORCE_CACHE。注意:如果你使用FORCE_CACHE请求缓存，缓存不存在，,OkHttp将返回一个504不可满足的请求响应。
- Canceling a Call 取消一个调用
当一个activity退出的时候，使用Call.cancel()立即停止一个正在进行中的调用，如果一个线程正在写一个请求或读一个响应,它将接收一个 IOException。下面请求服务端会有两秒延迟，客户端发出请求1秒的时候，请求还未完成，这个时候终止了请求，抛出了IOException。
private final ScheduledExecutorService 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") // This URL is served with a 2 second delay.
.build();
final long startNanos = System.nanoTime();
final Call call = client.newCall(request);
// Schedule a job 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 Canceled call.%n", (System.nanoTime() - startNanos) / 1e9f);
}
}, 1, TimeUnit.SECONDS);
try {
System.out.printf("%.2f Executing call.%n", (System.nanoTime() - startNanos) / 1e9f);
Response response = call.execute();
System.out.printf("%.2f Call was expected to fail, but completed: %s%n",
(System.nanoTime() - startNanos) / 1e9f, response);
} catch (IOException e) {
System.out.printf("%.2f Call failed as expected: %s%n",
(System.nanoTime() - startNanos) / 1e9f, e);
}
}- Timeouts 超时
访问服务器一般分为3部分，客服端和服务端建立连接connectTimeout，客户端发送数据到服务端writeTimeout，服务端将相应数据发送到客户端readTimeout，这三步每一步都有可能耗时，所以我们设置耗时时间非常有必要，超过某一部分时间就要抛出异常。
private final OkHttpClient client;
public ConfigureTimeouts() throws Exception {
client = new OkHttpClient.Builder()
.connectTimeout(10, TimeUnit.SECONDS)
.writeTimeout(10, TimeUnit.SECONDS)
.readTimeout(30, TimeUnit.SECONDS)
.build();
}
public void run() throws Exception {
Request request = new Request.Builder()
.url("http://httpbin.org/delay/2") // This URL is served with a 2 second delay.
.build();
Response response = client.newCall(request).execute();
System.out.println("Response completed: " + response);
}- Per-call Configuration 每个调用的设置
所有的HTTP客户端配置在OkHttpClient中,包括代理设置,超时和缓存。当你需要为单个调用改变配置的时候,调用OkHttpClient.newBuilder()，这返回一个builder,分享同样的连接池,分配器和原始OkHttpClient的配置。在下面的示例中,我们让一个请求500ms 超时,另一个请求3000 ms超时。
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
Request request = new Request.Builder()
.url("http://httpbin.org/delay/1") // This URL is served with a 1 second delay.
.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 处理身份验证
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());
} OkHttp可以自动重试未经身份验证的请求，当响应401未授权, 一个Authenticator被访问来提供证书，如果返回的响应码是code=401, message=Unauthorized ，则会调用OkHttpClient.Builder() 的authenticator 方法，对新的request对象调用header("Authorization", credential) ；如果返回的是407 proxy unauthorized ，则是不是服务器最终要求的客户端的登陆信息，就要调用OkHttpClient.Builder() 的proxyAuthenticator()方法，调用和上面一样，对新的request对象添加头部信息。如果用户名或者密码有问题，那么okhttp会一直使用这个错误的信息尝试，那么我们应该加一个判断，如果之前用该用户名和密码登陆失败了，就不应该再次登录：
if (credential.equals(response.request().header("Authorization"))) {
return null; // If we already failed with these credentials, don't retry.
}当你设置一个应用程序定义的限制时你也可以跳过重试:
if (responseCount(response) >= 3) {
return null; // If we've failed 3 times, give up.
}这上面的代码依赖于 responseCount() 方法:
private int responseCount(Response response) {
int result = 1;
while ((response = response.priorResponse()) != null) {
result++;
}
return result;
}四、总结
Okhttp很强大，我们看一下wiki基本上就可以上手，下一篇我会讲解拦截器和其他配置。