深入理解OkHttp3:(四)常用事例Demo
這裡彙總編寫了一些演示如何使用OkHttp解決常見問題的方法。通讀它們,瞭解它們是如何協同工作的。可以在需要的時候,隨意剪下貼上這些示例;
1.同步GET(Synchronous GET)
下載一個檔案,列印它的標題,並列印它的響應主體作為字串。
響應體(Body)上的string()方法對於小文件來說既方便又高效。但是,如果響應主體很大(大於1 MiB),請避免string(),因為它將把整個文件載入到記憶體中。在這種情況下,更喜歡把身體當作一個流來處理。
import java.io.IOException; import okhttp3.Headers; import okhttp3.OkHttpClient; import okhttp3.Request; import okhttp3.Response; public final class SynchronousGet { private final OkHttpClient client = new OkHttpClient(); public void run() throws Exception { Request request = new Request.Builder() .url("https://publicobject.com/helloworld.txt") .build(); try (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()); } } public static void main(String... args) throws Exception { new SynchronousGet().run(); } }
2.非同步GET(Asynchronous GET)
在工作執行緒上下載檔案,並在響應可讀時被呼叫。回撥是在響應Header就緒後進行的。讀取響應體仍然可能阻塞。OkHttp目前不提供非同步api分段來接收響應體。
import java.io.IOException; import okhttp3.Call; import okhttp3.Callback; import okhttp3.Headers; import okhttp3.OkHttpClient; import okhttp3.Request; import okhttp3.Response; import okhttp3.ResponseBody; public final class AsynchronousGet { 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 { try (ResponseBody responseBody = response.body()) { 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(responseBody.string()); } } }); } public static void main(String... args) throws Exception { new AsynchronousGet().run(); } }
3.訪問Headers(Accessing Headers)
通常HTTP報頭的工作方式類似於Map<String, String>:每個欄位都有一個值或沒有。但有些標頭允許多個值,比如Guava的Multimap。例如,HTTP響應提供多個不同的Headers是合法和常見的。OkHttp的api試圖讓所有情況都變得簡單易處理。
在編寫請求Headers時,使用Headers(名稱、值)方法將唯一出現的名稱設定為值。如果存在現有值,則在新增新值之前將刪除它們。使用addHeader(名稱、值)方法新增標題,而不刪除已經出現的標題。
在讀取響應Headers時,使用header(name)方法返回最後一次出現的value。通常這也是唯一可能發生的情況!如果不存在值,header(name)方法將返回null。要將欄位的所有值作為列表讀取,請使用headers(name)方法。
要訪問所有Header,請使用支援按索引訪問的Headers類。
import java.io.IOException;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
public final class AccessHeaders {
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();
try (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"));
}
}
public static void main(String... args) throws Exception {
new AccessHeaders().run();
}
}
4.用POST傳送一個字串(Posting a String)
使用HTTP POST向服務端傳送請求體。這個示例將標記文件傳送給使用HTML呈現的web服務端。同時因為整個請求主體在記憶體中,所以避免使用此API傳送較大(大於1 MiB)的文件。
import java.io.IOException;
import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;
public final class PostString {
public static final MediaType MEDIA_TYPE_MARKDOWN
= MediaType.get("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();
try (Response response = client.newCall(request).execute()) {
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}
}
public static void main(String... args) throws Exception {
new PostString().run();
}
}
5.傳送流(Post Streaming)
在這裡,我們將請求主體作為流傳送給服務端。這個請求主體的內容在編寫時生成。這個示例直接流到Okio緩衝接收器中。您的程式可能更喜歡OutputStream,您可以從BufferedSink.outputStream()中獲得它。
import java.io.IOException;
import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;
import okio.BufferedSink;
public final class PostStreaming {
public static final MediaType MEDIA_TYPE_MARKDOWN
= MediaType.get("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();
try (Response response = client.newCall(request).execute()) {
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}
}
public static void main(String... args) throws Exception {
new PostStreaming().run();
}
}
6.用Post方法傳送一個檔案(Posting a file)
用一個檔案來作為請求body,是一件很簡單的事情。
import java.io.File;
import java.io.IOException;
import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;
public final class PostFile {
public static final MediaType MEDIA_TYPE_MARKDOWN
= MediaType.get("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();
try (Response response = client.newCall(request).execute()) {
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}
}
public static void main(String... args) throws Exception {
new PostFile().run();
}
}
7.用post傳送表單資料到服務埠(Posting form parameters)
使用FormBody.Builder構建器來構建一個類似於HTML <form>標記的請求體。名稱和值將使用html相容的表單URL編碼進行編碼。
import java.io.IOException;
import okhttp3.FormBody;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;
public final class PostForm {
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();
try (Response response = client.newCall(request).execute()) {
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}
}
public static void main(String... args) throws Exception {
new PostForm().run();
}
}
8.釋出MultipartBody請求(Posting a multipartBody request)
MultipartBody.Builder構造器可以構建與HTML檔案上傳表單相容的複雜請求體。多部分請求體的每個部分本身就是請求體,可以定義自己的頭。如果存在,這些header應該描述對應部分主體,例如其內容配置。如果內容長度和內容型別header可用,則會自動新增它們。
import java.io.File;
import java.io.IOException;
import okhttp3.MediaType;
import okhttp3.MultipartBody;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;
public final class PostMultipart {
/**
* The imgur client ID for OkHttp recipes. If you're using imgur for anything other than running
* these examples, please request your own client ID! https://api.imgur.com/oauth2
*/
private static final String IMGUR_CLIENT_ID = "9199fdef135c122";
private static final MediaType MEDIA_TYPE_PNG = MediaType.get("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();
try (Response response = client.newCall(request).execute()) {
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}
}
public static void main(String... args) throws Exception {
new PostMultipart().run();
}
}
9.用Moshi解析JSON響應
Moshi是一個方便的API,用於在JSON和Java物件之間進行轉換。這裡,我們使用它從GitHub API解碼JSON響應。
注意,ResponseBody.charStream()使用Content-Type響應頭來確定解碼響應主體時使用的字符集。如果沒有指定字符集,則預設為UTF-8。
import com.squareup.moshi.JsonAdapter;
import com.squareup.moshi.Moshi;
import java.io.IOException;
import java.util.Map;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
public final class ParseResponseWithMoshi {
private final OkHttpClient client = new OkHttpClient();
private final Moshi moshi = new Moshi.Builder().build();
private final JsonAdapter<Gist> gistJsonAdapter = moshi.adapter(Gist.class);
public void run() throws Exception {
Request request = new Request.Builder()
.url("https://api.github.com/gists/c2a7c39532239ff261be")
.build();
try (Response response = client.newCall(request).execute()) {
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
Gist gist = gistJsonAdapter.fromJson(response.body().source());
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;
}
public static void main(String... args) throws Exception {
new ParseResponseWithMoshi().run();
}
}
10.Responses快取
要快取響應,您需要一個可以讀寫的快取目錄,以及對快取大小的限制。快取目錄應該是私有的,不受信任的應用程式不應該能夠讀取它的內容!
讓多個快取同時訪問同一個快取目錄是錯誤的。大多數應用程式應該只調用一次新的OkHttpClient(),使用它們的快取配置它,並在任何地方使用相同的例項。否則,這兩個快取例項將相互參雜在一起,破壞響應快取,並可能導致程式崩潰。
響應快取對所有配置使用HTTP Header。你可以新增像cache-control: max-stale=3600這樣的請求header,OkHttp的快取將會支援它們。您的服務端通過它自己的響應header來配置快取響應的時間,比如Cache-Control: max-age=9600。快取header用於強制快取響應、強制網路響應或強制使用條件GET驗證網路響應。
import java.io.File;
import java.io.IOException;
import okhttp3.Cache;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
public final class CacheResponse {
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();
String response1Body;
try (Response response1 = client.newCall(request).execute()) {
if (!response1.isSuccessful()) throw new IOException("Unexpected code " + response1);
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());
}
String response2Body;
try (Response response2 = client.newCall(request).execute()) {
if (!response2.isSuccessful()) throw new IOException("Unexpected code " + response2);
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));
}
public static void main(String... args) throws Exception {
new CacheResponse(new File("CacheResponse.tmp")).run();
}
}
要防止響應使用快取,請使用CacheControl.FORCE_NETWORK。為了防止它使用網路,使用CacheControl.FORCE_CACHE。注意:如果您使用FORCE_CACHE,並且響應需要網路,那麼OkHttp將返回一個504不可滿足的請求響應。
11.取消一個呼叫(Call)
使用call.cancel()方法立即停止正在進行的呼叫。如果執行緒當前正在編寫請求或讀取響應,它將收到IOException。當不再需要呼叫時,使用此方法節省網路資源;例如,當用戶從應用程式導航離開時。同步和非同步呼叫都可以取消。
import java.io.IOException;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import okhttp3.Call;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
public class CancelCall {
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);
System.out.printf("%.2f Executing call.%n", (System.nanoTime() - startNanos) / 1e9f);
try (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);
}
}
public static void main(String... args) throws Exception {
new CancelCall().run();
}
}
12.超時(Timeouts)
當呼叫的對等端不可到達時,使用timeouts來結束一次呼叫。網路分割槽可能是由於客戶端連線問題、伺服器可用性問題或兩者之間的任何問題。OkHttp支援連線、讀和寫超時。
import java.util.concurrent.TimeUnit;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
public final class ConfigureTimeouts {
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();
try (Response response = client.newCall(request).execute()) {
System.out.println("Response completed: " + response);
}
}
public static void main(String... args) throws Exception {
new ConfigureTimeouts().run();
}
}
13.更改單個Call的配置
所有HTTP客戶端配置都存在於OkHttpClient中,包括代理設定、超時和快取。當您需要更改單個Call的配置時,請呼叫OkHttpClient.newBuilder()。這將返回一個構建器,該構建器與原始客戶端共享相同的連線池、排程程式和配置。在下面的示例中,我們提出一個請求,超時時間為500毫秒,另一個請求超時時間為3000毫秒。
import java.io.IOException;
import java.util.concurrent.TimeUnit;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
public final class PerCallSettings {
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();
// Copy to customize OkHttp for this request.
OkHttpClient client1 = client.newBuilder()
.readTimeout(500, TimeUnit.MILLISECONDS)
.build();
try (Response response = client1.newCall(request).execute()) {
System.out.println("Response 1 succeeded: " + response);
} catch (IOException e) {
System.out.println("Response 1 failed: " + e);
}
// Copy to customize OkHttp for this request.
OkHttpClient client2 = client.newBuilder()
.readTimeout(3000, TimeUnit.MILLISECONDS)
.build();
try (Response response = client2.newCall(request).execute()) {
System.out.println("Response 2 succeeded: " + response);
} catch (IOException e) {
System.out.println("Response 2 failed: " + e);
}
}
public static void main(String... args) throws Exception {
new PerCallSettings().run();
}
}
14.處理身份驗證
OkHttp可以自動重試未經身份驗證的請求。如果沒有授權的401響應,則要求Authenticator提供證書。具體實現應該構建一個包含丟失證書的新請求。如果沒有證書可用,返回null以跳過重試。
使用Response.challenges()獲得任何身份驗證質詢的方案和領域。當完成一個基本的身份驗證質詢時,使用Credentials.basic(username, password)方法編碼請求Header。
import java.io.IOException;
import okhttp3.Authenticator;
import okhttp3.Credentials;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.Route;
public final class Authenticate {
private final OkHttpClient client;
public Authenticate() {
client = new OkHttpClient.Builder()
.authenticator(new Authenticator() {
@Override public Request authenticate(Route route, Response response) throws IOException {
if (response.request().header("Authorization") != null) {
return null; // Give up, we've already attempted to authenticate.
}
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();
try (Response response = client.newCall(request).execute()) {
if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
System.out.println(response.body().string());
}
}
public static void main(String... args) throws Exception {
new Authenticate().run();
}
}
為了避免在身份驗證不起作用時進行多次重試,您可以返回null以放棄。例如,當已經嘗試了這些確切的證書時,您應該可能想要跳過重試:
if (credential.equals(response.request().header("Authorization"))) {
return null; // If we already failed with these credentials, don't retry.
}
當達到應用程式定義的嘗試限制次數時,也可以跳過重試:
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;
}