Java 9+ HTTP2.0 API 入门与实践

英文链接:

https://labs.consol.de/development/2017/03/14/getting-started-with-java9-httpclient.html

英文好的可以直接看原文去——^_^

Java 9+ HTTP2.0 API 入门与实践

简述

如果您需要使用Java语言来请求HTTP资源,那么你可能会遇到多种解决方案,你最终可能会以一种合理的方式来达成这个目的 —– 引用第三方包。

Java9除了有模块化特性之外,还附带了一个全新的HTTP客户端API。不仅支持HTTP2.0,还提供了一套有亲和力的API。

HTTP2.0是啥子东东?

HTTP2.0带来了令人手舞足蹈的新特性:(这里不来自原文)

  • 二进制分帧
  • 请求/响应管线化
  • 异步连接
  • 多路复用
  • 服务器推送流(Server Push技术)
  • 基于TCP的长连接
  • 首部压缩

一句话描述:http/2最大的特点是使用多路复用,对同一个域的服务器只建立一次TCP连接,加载多个资源,使用二进制帧传输,同时会对http头部进行压缩。

就这样,我们瞧上了丰满的HTTP2.0。

孵化器模块

这里需要特别注意的是,在Java9中,HTTP客户端组件是随Java 9一起交付的孵化器模块,这里有几层意思注意:

  • 在 JDK 9, 这个模块叫做jdk.incubator.httpclient
  • incubator模块在JDK10将被java.httpclient所取代
  • JDK 10 可能會對 API 帶來重大更改。

Java 9的HTTP客户端API

基本上,通过HTTP进行通信时,会涉及到三个类:HttpClient将用于发送HttpRequest和接收HttpResponse。这API还是比较容易理解的:

基本示例:GET 请求,返回字符串

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
 .uri(new URI("https://labs.consol.de/"))
 .build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandler.asString());
System.out.println(response.statusCode());
System.out.println(response.body());

很优雅,对不对? 没有InputStream和Reader被涉及, - 转而是通过BodyHandler来直接从响应中获取字符串。不多赘述,将在下文介绍BodyHandlers。

虽然HttpClient,HttpRequest并且HttpResponse是HTTP2.0通信中的主要参与者,但我们还是要与Builder配合使用。Builder提供了一套简明易懂的API。

HttpRequest.Builder

我们可以通过调用HttpRequest.newBuilder()来获取一个HttpRequest.Builder实例,就像第一个示例中那样。 我们将使用它来配置与特定请求相关的所有内容。下面是源代码:

// HttpRequest.Builder
public abstract static class Builder {
 // note: some methods left out for the sake of brevity
 public abstract Builder uri(URI uri);
 public abstract Builder version(HttpClient.Version version);
 public abstract Builder header(String name, String value);
 public abstract Builder timeout(Duration duration);
 public abstract Builder GET();
 public abstract Builder POST(BodyProcessor body);
 public abstract Builder PUT(BodyProcessor body);
 public abstract Builder DELETE(BodyProcessor body);
 public abstract HttpRequest build();
}

可读性很好(自解释型)。采用链式方法调用来完成请求内容的配置,然后调用build()获取HttpRequest实例。

HttpClient.Builder

与HttpRequest类似,我们调用HttpClient.newBuilder()来获取HttpClient.Builder实例。它提供了一个API来配置一些关于我们的连接的更通用的东西。 下面是源代码:

// HttpClient.Builder
public abstract static class Builder {
 public abstract Builder cookieManager(CookieManager cookieManager);
 public abstract Builder sslContext(SSLContext sslContext);
 public abstract Builder sslParameters(SSLParameters sslParameters);
 public abstract Builder executor(Executor executor);
 public abstract Builder followRedirects(Redirect policy);
 public abstract Builder version(HttpClient.Version version);
 public abstract Builder priority(int priority);
 public abstract Builder proxy(ProxySelector selector);
 public abstract Builder authenticator(Authenticator a);
 public abstract HttpClient build();
}

良好的自解释性帮助IDE能够更好地达成你的目的。

更多Java 9 HTTP客户端应用示例

上面见识到了这套前景光明的API,下面让我们来看看更多的关于它的应用示例吧。

1. 保存GET请求到文件

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
 .uri(new URI("https://labs.consol.de/"))
 .GET()
 .build();
Path tempFile = Files.createTempFile("consol-labs-home", ".html");
HttpResponse<Path> response = client.send(request, HttpResponse.BodyHandler.asFile(tempFile));
System.out.println(response.statusCode());
System.out.println(response.body());

2. 通过POST上传文件

用POST上传本地文件也变得十分简单,使用HttpRequest.BodyProcessor:

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
 .uri(new URI("http://localhost:8080/upload/"))
 .POST(HttpRequest.BodyProcessor.fromFile(Paths.get("/tmp/file-to-upload.txt")))
 .build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandler.discard(null));
System.out.println(response.statusCode());

3. 异步HTTP请求

异步HTTP请求也变得简单,由HttpClient#sendAsync()代替HttpClient#send。如果服务端支持,你甚至可以取消执行中的请求:

HttpClient client = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
 .uri(new URI("https://labs.consol.de/"))
 .GET()
 .build();
CompletableFuture<HttpResponse<String>> response = client.sendAsync(request, HttpResponse.BodyHandler.asString());
Thread.sleep(5000);
if(response.isDone()) {
 System.out.println(response.get().statusCode());
 System.out.println(response.get().body());
} else {
 response.cancel(true);
 System.out.println("Request took more than 5 seconds... cancelling.");
}

4. 使用系统代理设置

HttpClient client = HttpClient.newBuilder()
 
 .proxy(ProxySelector.getDefault())
 .build();
 HttpRequest request = HttpRequest.newBuilder()
 .uri(new URI("https://labs.consol.de"))
 .GET()
 .build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandler.asString());
 System.out.println(response.statusCode());
 System.out.println(response.body());

5.基本认证 Basic Authentication

HttpClient client = HttpClient.newBuilder()
 .authenticator(new Authenticator() {
 @Override
 protected PasswordAuthentication getPasswordAuthentication() {
 return new PasswordAuthentication("username", "password".toCharArray());
 }
 })
 .build();
HttpRequest request = HttpRequest.newBuilder()
 .uri(new URI("https://labs.consol.de"))
 .GET()
 .build();
HttpResponse<String> response = client.send(request, HttpResponse.BodyHandler.asString());
System.out.println(response.statusCode());
System.out.println(response.body());

结论

上面的例子表明,使用Java 9的标准API来发送HTTP请求会更简便。 此外,我们将能以优雅的方式处理响应。当然,某些第三方包也有类似喜人的功能,但总得选择一种体面的开箱即用的解决方案,比如自带的好东东。

api

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