java中发送http请求

使用HttpClient发送http请求：

public String cawl(String url){
        try {
            CloseableHttpClient httpClient = HttpClientBuilder.create().build();//初始化
            CloseableHttpResponse httpResponse = httpClient.execute(new HttpGet(url));//获取页面信息
            String result = EntityUtils.toString(httpResponse.getEntity());//将对象转换成字符串输出
            return result;
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
 }

使用Url发送http请求：

抽象类URLConnection:所有类的超类，它代表应用程序和 URL 之间的通信链接。此类的实例可用于读取和写入此 URL 引用的资源

 try {
            URL url = new URL("http://www.baidu.com");
            URLConnection connection = url.openConnection();
            for (int i = 1;;i++){
                String header = connection.getHeaderField(i);
                if (header==null)break;
                System.out.println(connection.getHeaderFieldKey(i)+":"+header);
            }
        } catch (java.io.IOException e) {
            e.printStackTrace();
        }

底层方面使用，Socket来发送http请求：

public void testCustom(){
        try {
            Socket socket = new Socket();
            InetSocketAddress addr = new InetSocketAddress("baidu.com",80);
            socket.connect(addr);
            InputStream in = socket.getInputStream();
            new Thread(new GetInfo(in)).start();//开线程来读取信息
            OutputStream out = socket.getOutputStream();
            out.write(("GET / HTTP/1.1\r\nHost: baidu.com\r\n" +     //  \r\n代表换行
                    "Accept-Language: zh-CN,zh;q=0.9\r\n" +
                    "Accept-Encoding: gzip, deflate, br\r\n" +
                    "User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) " +
                    "AppleWebKit/537.36 (KHTML, like Gecko) " +
                    "Chrome/63.0.3239.108 Safari/537.36\r\n\r\n").getBytes());
            out.flush();
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

因为baidu.com采用的是https协议，使用了SSL加密，所以控制台输出以下信息：

 ready to read
HTTP/1.1 302 Moved Temporarily
Server: bfe/1.0.8.18
Date: Thu, 15 Mar 2018 08:26:58 GMT
Content-Type: text/html
Content-Length: 161
Connection: Keep-Alive
Location: https://www.baidu.com/
Expires: Fri, 16 Mar 2018 08:26:58 GMT
Cache-Control: max-age=86400
Cache-Control: privae

当网址换成http协议时，出现了以下的信息：

ready to read
HTTP/1.1 200 OK
Server: nginx
Date: Thu, 15 Mar 2018 08:32:04 GMT
Content-Type: text/html;charset=UTF-8
Transfer-Encoding: chunked
Connection: keep-alive
Vary: Accept-Encoding
Cache-Control: max-age=86400
Last-Modified: Thu, 15 Mar 2018 08:32:04 GMT
Expires: Fri, 16 Mar 2018 08:32:04 GMT
X-Frame-Options: SAMEORIGIN
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
Content-Encoding: gzip

2228


因为网站的文档编码是：gzip，需要进行解码才能读取，而后直接读取apache的网址,就出现header+页面代码，就不附控制台的输出结果了。

参考文档：

http://www.jb51.net/article/114738.htm

http://blog.csdn.net/u010197591/article/details/51441399