我們寫(xiě)了一些方法來(lái)示例如果使用OkHttp來(lái)解決常見(jiàn)問(wèn)題。通讀它們了解它們是如何一起工作的。隨意地進(jìn)行復(fù)制、粘貼，這是它們存在的目的。
同步Get請(qǐng)求
下載一個(gè)文件，打印它的頭，并將其響應(yīng)主體以字符串形式打印。
作用在響應(yīng)主體上的string()方法對(duì)于小文檔來(lái)說(shuō)是方便和高效的。但是如果響應(yīng)主體比較大(大于1MB)，避免使用string()，因?yàn)樗鼤?huì)加載整個(gè)文檔到內(nèi)存中。在這種情況下，優(yōu)先使用stream來(lái)處理主體。
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());
}
異步Get請(qǐng)求
在一個(gè)工作線程下載一個(gè)文件，當(dāng)響應(yīng)可讀時(shí)獲取回調(diào)。這個(gè)回調(diào)將在響應(yīng)頭準(zhǔn)備好時(shí)執(zhí)行。讀取響應(yīng)主體可能仍然阻塞。OkHttp當(dāng)前沒(méi)有提供異步API來(lái)局部地接收響應(yīng)主體。
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());
}
});
}
訪問(wèn)Header
典型的HTTP頭工作起來(lái)像一個(gè)Map< String, String >，每一個(gè)字段有一個(gè)值或沒(méi)有值。但是有一些頭允許多個(gè)值，像Guava的Multimap。對(duì)于一個(gè)HTTP響應(yīng)來(lái)應(yīng)用多個(gè)Vary頭是合法的并且常見(jiàn)的。OkHttp的API試圖兼容這些情況。
當(dāng)寫(xiě)請(qǐng)求頭時(shí)，使用header(name, value)的方式來(lái)設(shè)置唯一出現(xiàn)的鍵值。如果已有值，會(huì)在新值添加前移除已有值。使用addHeader(name, value)來(lái)添加一個(gè)頭而不移除已經(jīng)存在的頭。
當(dāng)讀取一個(gè)響應(yīng)頭時(shí)，使用header(name)來(lái)返回最后一次出現(xiàn)的鍵值對(duì)。通常這是唯一出現(xiàn)的鍵值對(duì)。如果不存在值，header(name)會(huì)返回null。使用headers(name)來(lái)用一個(gè)list讀取一個(gè)字段的所有值。
使用支持按索引訪問(wèn)的Headers類來(lái)訪問(wèn)所有的頭。
private final OkHttpClient client = new OkHttpClient();
public void run() throws Exception {
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();
Response response = client.newCall(request).execute();
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println("Server: " + response.header("Server"));
System.out.println("Date: " + response.header("Date"));
System.out.println("Vary: " + response.headers("Vary"));
}
上傳字符串
使用HTTP POST來(lái)發(fā)送請(qǐng)求主體到服務(wù)器。這個(gè)例子上傳了一個(gè)markdown文檔到一個(gè)用HTML渲染markdown的服務(wù)器中。因?yàn)檎麄€(gè)請(qǐng)求主體同時(shí)存在內(nèi)存中，避免使用這個(gè)API上傳大的文檔(大于1MB)。
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());
}
上傳流
這里以stream的形式上傳請(qǐng)求主體。請(qǐng)求主體的內(nèi)容如它寫(xiě)入的進(jìn)行生成。這個(gè)示例stream直接放入到了Okio緩存sink中。你的程序可能需要一個(gè)OutputStream，你可以從BufferedSink.outputStream()中獲取。
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());
}
上傳文件
使用文件作為請(qǐng)求主體很容易。
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());
}
上傳表格參數(shù)
使用FormBody.Builder來(lái)構(gòu)建一個(gè)工作起來(lái)像HTML< form >標(biāo)簽的請(qǐng)求主體。鍵值對(duì)會(huì)使用一個(gè)兼容HTML form的URL編碼進(jìn)行編碼。
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());
}
上傳多部分請(qǐng)求
MultipartBody.Builder可以構(gòu)造復(fù)雜的請(qǐng)求主體與HTML文件上傳表單兼容。multipart請(qǐng)求主體的每部分本身就是一個(gè)請(qǐng)求主體，可以定義它自己的頭。如果存在自己的頭，那么這些頭應(yīng)該描述部分主體，例如它的Content-Disposition。Content-Length和Content-Type會(huì)在其可用時(shí)自動(dòng)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());
}
使用Gson解析Json響應(yīng)
Gson是一個(gè)便利API來(lái)實(shí)現(xiàn)JSON和Java對(duì)象之間的轉(zhuǎn)化。這里我們使用它來(lái)解碼來(lái)自GitHub API的JSON響應(yīng)。
ResponseBody.charStream()使用響應(yīng)頭Content-Type來(lái)確定在解碼響應(yīng)主體時(shí)使用哪個(gè)字符集。如果沒(méi)有指定字符集，則默認(rèn)使用UTF-8.
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;
}
響應(yīng)緩存
要緩存響應(yīng)，你需要一個(gè)進(jìn)行讀取和寫(xiě)入的緩存目錄，以及一個(gè)緩存大小的限制。緩存目錄應(yīng)該是私有的，且不被信任的應(yīng)用不能夠讀取它的內(nèi)容。
讓多個(gè)緩存同時(shí)訪問(wèn)相同的混存目錄是錯(cuò)誤的。大多數(shù)應(yīng)用應(yīng)該只調(diào)用一次new OkHttpClient()，配置它們的緩存，并在所有地方使用相同的實(shí)例。否則兩個(gè)緩存實(shí)例會(huì)相互進(jìn)行干涉，腐朽響應(yīng)緩存，有可能造成你的程序崩潰。
響應(yīng)緩存使用HTTP頭進(jìn)行所有配置。你可以添加像Cache-Control:max-stale=3600這樣的請(qǐng)求頭并且OkHttp的緩存會(huì)尊重它們。你的服務(wù)器使用自己的響應(yīng)頭像Cache-Control:max-age=9600來(lái)配置響應(yīng)緩存多久。這里有緩存頭來(lái)強(qiáng)制一個(gè)緩存響應(yīng)，強(qiáng)制一個(gè)網(wǎng)絡(luò)響應(yīng)，強(qiáng)制使用一個(gè)條件的GET來(lái)驗(yàn)證網(wǎng)絡(luò)響應(yīng)。
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));
}
使用CacheControl.FORCE_NETWORK來(lái)阻止響應(yīng)使用緩存。使用CacheContril.FORCE_CACHE來(lái)阻止使用網(wǎng)絡(luò)。注意：如果你使用FORCE_CACHE且響應(yīng)需要網(wǎng)絡(luò)，OkHttp會(huì)返回一個(gè)504 Unsatisfiable Request響應(yīng)。
取消調(diào)用
使用Call.cancel()來(lái)立即停止一個(gè)正在進(jìn)行的調(diào)用。如果一個(gè)線程正在寫(xiě)請(qǐng)求或讀響應(yīng)，它會(huì)接收到一個(gè)IOException。當(dāng)一個(gè)調(diào)用不再需要時(shí)，使用這個(gè)來(lái)節(jié)省網(wǎng)絡(luò)，例如當(dāng)用戶從應(yīng)用離開(kāi)。同步和異步調(diào)用都可以取消。
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);
}
}
超時(shí)
使用超時(shí)來(lái)使調(diào)用在當(dāng)另一端沒(méi)有到達(dá)時(shí)失敗。網(wǎng)絡(luò)部分可能是由于連接問(wèn)題，服務(wù)器可用性問(wèn)題或者其他。OkHttp支持連接、讀取和寫(xiě)入超時(shí)。
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);
}
單獨(dú)配置調(diào)用
所有HTTP client配置都存在OkHttpClient中，包括代理設(shè)置，超時(shí)和緩存。當(dāng)你需要改變一個(gè)單獨(dú)call的配置時(shí)，調(diào)用OkHttpClient.newBuilder()。這個(gè)會(huì)返回一個(gè)builder，與原始的client共享下共同的連接池，調(diào)度器和配置。在下面的例子中，我們讓一個(gè)請(qǐng)求有500ms的超時(shí)而另一個(gè)有3000ms的超時(shí)。
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);
}
}
處理認(rèn)證
OkHttp會(huì)自動(dòng)重試未認(rèn)證請(qǐng)求。當(dāng)一個(gè)響應(yīng)為401 Not Authorized時(shí)，會(huì)要求Authenticator來(lái)應(yīng)用證書(shū)。Authenticator的實(shí)現(xiàn)應(yīng)該構(gòu)建一個(gè)包含缺失證書(shū)的新請(qǐng)求。如果沒(méi)有證書(shū)可用，返回null來(lái)跳過(guò)重試。
使用Response.challenges()來(lái)獲取所有認(rèn)證挑戰(zhàn)的模式和領(lǐng)域。當(dāng)完成一個(gè)Basic挑戰(zhàn)時(shí)，使用Credentials.basic(username，password)來(lái)編碼請(qǐng)求頭。
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());
}
為了避免當(dāng)認(rèn)證無(wú)法工作時(shí)過(guò)多的嘗試，你可以返回null來(lái)放棄。例如，當(dāng)這些明確的證書(shū)已經(jīng)嘗試過(guò)了，你可能想跳過(guò)。
if (credential.equals(response.request().header("Authorization"))) {
return null; // If we already failed with these credentials, don't retry.
}
你可能也想在達(dá)到應(yīng)用定義的嘗試限制次數(shù)時(shí)跳過(guò)嘗試：
if (respondseCount(response) >= 3) {
return null; // If we've failed 3 times, give up.
}
上面的代碼依賴這個(gè)responseCount()方法：
private int responseCount(Response response) {
int result = 1;
while ((response = response.priorResponse()) != null) {
result++;
}
return result;
}
原文鏈接：
https://github.com/square/okhttp/wiki/Recipes
OkHttp官方文檔系列文章：
