java.net 发送http请求

代码：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;

/**
 * Created by deng on 2020/3/24.
 * 发送HTTP请求
 */
public class HttpClient {

    public static void main(String[] args) {
        String url = "https://www.baidu.com";
        String s = HttpClient.sendHttpRequest(url, RequestMethod.GET);
        System.out.println(s);
    }

    /**
     * @param urlParam  url
     * @param requestMethod 请求方式
     * @return  返回String类型的字符串 ，如果请求失败，返回null
     */
    public static String sendHttpRequest(String urlParam,RequestMethod requestMethod){
        HttpURLConnection con = null;
        BufferedReader buffer = null;
        StringBuffer resultBuffer = null;
        InputStream ins = null;
        try {
            URL url = new URL(urlParam);
            //得到连接对象
            con = (HttpURLConnection) url.openConnection();

            //设置请求类型
            switch (requestMethod){
                case GET:
                    con.setRequestMethod("GET");
                    break;
                case POST:
                    con.setRequestMethod("POST");
                    break;
            }
            //据说post请求必须设置这两条,暂时不知道
            con.setDoOutput(true);  //允许写出
            con.setDoInput(true);   //允许读入

            con.setUseCaches(false);    //不使用缓存

            //得到响应码
            int responseCode = con.getResponseCode();

            if(responseCode == HttpURLConnection.HTTP_OK){
                //请求成功，得到响应流
                ins = con.getInputStream();
                //转化为字符串
                resultBuffer = new StringBuffer();
                String line;
                //注意响应体的编码格式，可能会有乱码
                buffer = new BufferedReader(new InputStreamReader(ins,"GBK"));

                while((line=buffer.readLine())!=null){
                    resultBuffer.append(line);
                }
                //将resultBuffer返回即可
                return resultBuffer.toString();
            }

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(ins!=null){
                try {
                    ins.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        return null;
    }
}

enum RequestMethod{
    GET,    //get请求
    POST    //post请求
}