一、HttpURLConnection发送GET请求

public static void GETRequest(int page,String cookie) throws Exception {
        String url = String.format("http://www.baidu.com/user?tn=baidu&pn=%s",page);
        //创建远程url连接对象
        URL obj = new URL(url);
        //通过远程url对象打开一个连接，强制转换为HttpUrlConnection类型
        HttpURLConnection con = (HttpURLConnection) obj.openConnection();
        //默认值我GET
        con.setRequestMethod("GET");
　　　　	con.setConnectTimeout(15000);	//设置连接主机服务器超时时间：15000毫秒
　　　　	con.setReadTimeout(60000);		//设置读取远程返回的数据时间：60000毫秒
        con.setDoInput(true);        	//设置输入流采用字节流
        con.setDoOutput(true);        	//设置输出流采用字节流
        //添加请求头
        con.setRequestProperty("User-Agent", "Mozilla/5.0 (Macintosh; U; PPC Mac OS X 10.5; zh-CN; rv:1.9.2.15) Gecko/20110303 Firefox/3.6.15");
        con.setRequestProperty("Host", "www.baidu.com");
//        con.setRequestProperty("Accept-Encoding","gzip, deflate");
        con.setRequestProperty("Accept-Language", "zh-CN,zh;q=0.9");
        con.setRequestProperty("Connection", "keep-alive");
        con.setRequestProperty("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9");
        con.setRequestProperty("Cookie", cookie);


//        状态码,getResponseCode()隐形调用了httpConn.connect()
        int responseCode = con.getResponseCode();

        System.out.println("Sending 'GET' request to URL : " + url);
        System.out.println("Response Code : " + responseCode);

        BufferedReader in = new BufferedReader(
                new InputStreamReader(con.getInputStream(), "gb2312"));
        String inputLine;
        StringBuffer response = new StringBuffer();

        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine);
        }
        System.out.println(response);
        in.close();
}

二、HttpURLConnection发送POST请求

public static void POSTRequest(String cookie) throws IOException {
        String param = "username=admin&password=admin";
        String url = "http://www.baidu.com/user/userlogin";
        //创建远程url连接对象
        URL obj = new URL(url);
        //通过远程url对象打开一个连接，强制转换为HttpUrlConnection类型
        HttpURLConnection con = (HttpURLConnection) obj.openConnection();
        //默认值我GET
        con.setRequestMethod("POST");
　　　　	con.setConnectTimeout(15000);	//设置连接主机服务器超时时间：15000毫秒
　　　　	con.setReadTimeout(60000);		//设置读取远程返回的数据时间：60000毫秒
        con.setDoInput(true);        	//设置输入流采用字节流
        con.setDoOutput(true);        	//设置输出流采用字节流
        //添加请求头
        con.setRequestProperty("User-Agent", "Mozilla/5.0 (Macintosh; U; PPC Mac OS X 10.5; zh-CN; rv:1.9.2.15) Gecko/20110303 Firefox/3.6.15");
        con.setRequestProperty("Host", "www.baidu.com");
//        con.setRequestProperty("Accept-Encoding","gzip, deflate");
        con.setRequestProperty("Accept-Language", "zh-CN,zh;q=0.9");
        con.setRequestProperty("Connection", "keep-alive");
        con.setRequestProperty("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9");
        con.setRequestProperty("Cookie", cookie);

        OutputStream output = con.getOutputStream();
        //写入参数输出流
        output.write(param.getBytes());
        OutputStreamWriter outr = new OutputStreamWriter(output, StandardCharsets.UTF_8);
        outr.flush();
        outr.close();

        //状态码
        int responseCode = con.getResponseCode();
        System.out.println("Sending 'POST' request to URL : " + url);
        System.out.println("Response Code : " + responseCode);

        BufferedReader in = new BufferedReader(
                new InputStreamReader(con.getInputStream(), StandardCharsets.UTF_8));
        String inputLine;
        StringBuffer response = new StringBuffer();

        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine);
        }
        in.close();

        //打印结果
        System.out.println(response.toString());
    }

三、关于respond中set-cookie值的获取

• 在HttpURLConnection中t常用两个方法获得响应中的header，getHeaderField()方法仅限于获取header中的不重复项，例如某个响应中的set-cookie有多个值，那么getHeaderField()方法仅返回最后一个set-cookie的值，那么此时我们可以使用getHeaderFields()方法，此方法返回一个Map，其包含所有的header中的数据

/**
Returns the value of the named header field.
If called on a connection that sets the same header multiple times with possibly different values, only the last value is returned.
Params:
name – the name of a header field.
Returns:
the value of the named header field, or null if there is no such field in the header.
**/
public String getHeaderField(String name);

/**
Returns an unmodifiable Map of the header fields. The Map keys are Strings that represent the response-header field names. Each Map value is an unmodifiable List of Strings that represents the corresponding field values.
Returns:
a Map of header fields
**/
public Map<String,List<String>> getHeaderFields()

四、HttpURLConnection乱码问题

在HttpURLConnection中出现乱码的情况主要有两种，我们需要定位乱码出现在哪个位置再解决，这个问题其他博主都写过很多的解决方法，这里不再详细说明。但是我在向一个比较古老的php发送请求时，返回的html内容乱码，我在将header中的Accept-Encoding注释掉以后，返回内容奇迹般的恢复了正常，使用各种方法都不能解决响应乱码的兄弟们可以试试