Java8中基于OkHttp3编写HTTP2客户端详解

客官°小女子只卖身不卖艺 2022-05-21 07:47 229阅读 0赞

显然，我们必须在Java还没有准备好支持HTTP2客户端编程的情况下（即使用Java 8及以下版本），提供HTTP2客户端应用的解决方案。目前流行的类库如下：

*  OkHttp
 *  Eclipse Jetty
 *  Netty
 *  Apache HttpComponents (Apache HC)

其中，Eclipse Jetty和Netty都同时提供客户端和服务端。而曾经广泛使用的Apache HC已经逐渐掉队，至今没有正式支持HTTP2的版本发布。所以这里特别推荐OkHttp，而且OkHttp还适合在Android应用中作为HTTP客户端。

OkHttp的最新版本3.10.0，2018年2月25日发布，特性如下：

*  支持HTTP2，默认采用TLS 1.2
 *  GZIP压缩
 *  缓存响应对象

在Maven项目中，pom.xml配置如下：

<dependency>
      <groupId>com.squareup.okhttp3</groupId>
      <artifactId>okhttp</artifactId>
      <version>3.10.0</version>
    </dependency>

编写HTTP2客户端应用如下：

1. 创建OkHttpClient

1.1 默认配置

OkHttpClient client = new OkHttpClient();

1.2 定制配置

OkHttpClient client = new OkHttpClient
    	.Builder()
    	.authenticator(new Authenticator() {...}
    	.build();

2. 创建请求

2.1 GET请求

Request request = new Request.Builder()
            .url("https://www.mydomain.com/")
            .build();//GET by default

2.2 POST请求

RequestBody strBody = RequestBody.create(MediaType.parse("text/x-markdown; charset=utf-8"), postBodyStr);
    RequestBody jsonBody = RequestBody.create(MediaType.parse("application/json; charset=utf-8"), postBodyJsonStr);

Request request = new Request.Builder()
            .url("https://www.mydomain.com")
            .post(mybody)
            .build();

3. 发送请求并处理响应

3.1 同步请求

Response response = client.newCall(request).execute(){//synch call
    	if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);
    		System.out.println(response.body().string());
    }

3.2 异步请求

client.newCall(request).enqueue(new Callback() {//asynch call
          @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());
            }
          }
    });

4. OkHttp访问HTTPS服务

final TrustManager[] trustAllCerts = new TrustManager[]{
        new X509TrustManager() {
            @Override
            public void checkClientTrusted(java.security.cert.X509Certificate[] chain, String authType) throws CertificateException {}
    
            @Override
            public void checkServerTrusted(java.security.cert.X509Certificate[] chain, String authType) throws CertificateException {}
    
            @Override
            public java.security.cert.X509Certificate[] getAcceptedIssuers() {
                return new java.security.cert.X509Certificate[]{};
            }
        }
    };
    
    final HostnameVerifier verifiedAllHostname = new HostnameVerifier() {
        @Override
        public boolean verify(String hostname, SSLSession session) {
            return true;
        }
    };
    
    SSLContext sslContext = SSLContext.getInstance("TLS");
    sslContext.init(null, trustAllCerts, new java.security.SecureRandom());
    SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();
    
    OkHttpClient client = new OkHttpClient.Builder()
        .sslSocketFactory(sslSocketFactory, (X509TrustManager) trustAllCerts[0]);
        .hostnameVerifier(verifiedAllHostname)
        .connectTimeout(60, TimeUnit.SECONDS)
        .readTimeout(60, TimeUnit.SECONDS)
        .writeTimeout(60, TimeUnit.SECONDS)
        .retryOnConnectionFailure(true)
        .build();
    
    Request request = new Request.Builder()
        .url("https://localhost:9443/hello")
        .build();
    
    Response response = client.newCall(request).execute();
    System.out.println(response.body().string());

这里我们只使用OkHttp原生API编写HTTP2客户端应用。在Spring Boot 2.0版本中，我们还可以使用Spring Boot starters for OkHttp，辅助编写HTTP2客户端。

参考链接：

http://square.github.io/okhttp/

https://www.eclipse.org/jetty

http://netty.io/

https://hc.apache.org/

https://github.com/freefair/okhttp-spring-boot