HTTP Components简介

基于版本4.5.x

简介

组件

• HttpClient，核心组件
• HC Fluent，提供了流式操作接口
• HttpMime，提供文件上传时用到的一些工具类
• HttpClient Cache，有待学习
• HttpClient OSGi，有待学习

特性

• 基于标准、纯净的Java语言。实现了Http1.0和Http1.1
• 以可扩展的面向对象的结构实现了Http全部的方法（GET, POST, PUT, DELETE, HEAD, OPTIONS, and TRACE）。
• 支持HTTPS（基于SSL的HTTP）协议。
• 通过HTTP代理建立透明的连接。
• 利用CONNECT方法通过HTTP代理建立隧道的HTTPS连接。
• Basic, Digest, NTLMv1, NTLMv2, NTLM2 Session, SNPNEGO, Kerberos认证方案。
• 插件式的自定义认证方案。
• 便携可靠的套接字工厂使它更容易的使用第三方解决方案(Pluggable secure socket factories, making it easier to use third party solutions)。
• 支持多线程应用的连接管理器。支持设置最大连接数，同时支持设置每个主机的最大连接数，发现并关闭过期的连接。
• 自动处理Set-Cookie中的Cookie。（Automatic Cookie handling for reading Set-Cookie: headers from the server and sending them back out in a Cookie: header when appropriate.）
• 插件式的自定义Cookie策略。
• Request的输出流可以避免流中内容直接缓冲到socket服务器。（Request output streams to avoid buffering any content body by streaming directly to the socket to the server.）
• Response的输入流可以有效的从socket服务器直接读取相应内容。
• 在http1.0和http1.1中利用KeepAlive保持持久连接。
• 直接获取服务器发送的response code和 headers。
• 可设置连接超时。
• 支持http1.1 response caching。
• 源代码基于Apache License 可免费获取。

Quick Start

HTTP Client

GET请求、POST请求 及 response处理

CloseableHttpClient httpclient = HttpClients.createDefault();

//GET请求及response处理
HttpGet httpGet = new HttpGet("http://targethost/homepage");
CloseableHttpResponse response1 = httpclient.execute(httpGet);
// The underlying HTTP connection is still held by the response object
// to allow the response content to be streamed directly from the network socket.
// In order to ensure correct deallocation of system resources
// the user MUST call CloseableHttpResponse#close() from a finally clause.
// Please note that if response content is not fully consumed the underlying
// connection cannot be safely re-used and will be shut down and discarded
// by the connection manager. 
try {
    System.out.println(response1.getStatusLine());
    HttpEntity entity1 = response1.getEntity();
    // do something useful with the response body
    // and ensure it is fully consumed
    EntityUtils.consume(entity1);
} finally {
    response1.close();
}

//POST请求及response处理
HttpPost httpPost = new HttpPost("http://targethost/login");
List <NameValuePair> nvps = new ArrayList <NameValuePair>();
nvps.add(new BasicNameValuePair("username", "vip"));
nvps.add(new BasicNameValuePair("password", "secret"));
httpPost.setEntity(new UrlEncodedFormEntity(nvps));
CloseableHttpResponse response2 = httpclient.execute(httpPost);

try {
    System.out.println(response2.getStatusLine());
    HttpEntity entity2 = response2.getEntity();
    // do something useful with the response body
    // and ensure it is fully consumed
    EntityUtils.consume(entity2);
} finally {
    response2.close();
}

官网的例子注释中有几点是需要注意的：

• 调用httpclient.execute(XXX)后，http连接会一直被response持有，需要调用CloseableHttpResponse#close()，当然也可是已使用jdk1.7的try-catch-resource。
• 如果response没有充分的被消耗掉（比如：chunk模式下，只取了部分），会被connection manager丢弃而不能复用，使用EntityUtils.consume(entity)可以确保response被充分消耗

HC Fluent 的流式接口

Request.Get("http://targethost/homepage")
    .execute().returnContent();
Request.Post("http://targethost/login")
    .bodyForm(Form.form().add("username",  "vip").add("password",  "secret").build())
    .execute().returnContent();

HttpMime 提交文件

multipart/form 类型的POST，下面例子中的FileBody、StringBody、MultipartEntityBuilder等都是HttpMine模块中的类。

public class ClientMultipartFormPost {

    public static void main(String[] args) throws Exception {
        if (args.length != 1)  {
            System.out.println("File path not given");
            System.exit(1);
        }
        CloseableHttpClient httpclient = HttpClients.createDefault();
        try {
            HttpPost httppost = new HttpPost("http://localhost:8080" +
                    "/fileUpload");

            FileBody bin = new FileBody(new File(args[0]));
            StringBody comment = new StringBody("A binary file of some kind", ContentType.TEXT_PLAIN);

            HttpEntity reqEntity = MultipartEntityBuilder.create()
                    .addPart("bin", bin)
                    .addPart("comment", comment)
                    .build();


            httppost.setEntity(reqEntity);

            System.out.println("executing request " + httppost.getRequestLine());
            CloseableHttpResponse response = httpclient.execute(httppost);
            try {
                System.out.println("----------------------------------------");
                System.out.println(response.getStatusLine());
                HttpEntity resEntity = response.getEntity();
                if (resEntity != null) {
                    System.out.println("Response content length: " + resEntity.getContentLength());
                }
                EntityUtils.consume(resEntity);
            } finally {
                response.close();
            }
        } finally {
            httpclient.close();
        }
    }

}

参考

HTTP Client使用详解
HttpClient Quick start