HttpClient 调用其它系统接口的工具类（post、get请求）

功能介绍：

1）实现了所有 HTTP 的方法（GET,POST,PUT,HEAD 等）

2）支持自动转向

3）支持 HTTPS 协议

4）支持代理服务器等

HttpClient最重要的功能是执行HTTP方法：执行一个HTTP方法涉及一个或多个HTTP请求/ HTTP响应信息交流，通常是由HttpClient内部处理。用户提供一个请求对象，HttpClient发送请求到目标服务器，希望服务器返回一个相应的响应对象，或者抛出一个异常（如果执行失败）。

示例工具类：

package com.forezp;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;
import java.util.Map;

public class HttpClientUtils {
         /**
         * 向指定URL发送GET方法的请求
         *
         * @param url   发送请求的URL 例如：http://localhost:8080/demo/login
         * @param param 请求参数 例：{ "userName":"admin", "password":"123456" }
         * @return URL 所代表远程资源的响应结果
         */
        public static String sendGet(String url, Map<String, Object> param) {
            StringBuilder result = new StringBuilder();
            BufferedReader in = null;
            try {
                URL realUrl = createURL(url, param);
                HttpURLConnection conn = (HttpURLConnection) realUrl.openConnection();
                conn.setRequestProperty("accept", "*/*");
                conn.setRequestProperty("connection", "Keep-Alive");
                conn.setRequestProperty("Charset", "UTF-8");
                conn.connect();
                in = new BufferedReader(new InputStreamReader(
                        conn.getInputStream()));
                String line;
                while ((line = in.readLine()) != null) {
                    result.append(line);
                }
            } catch (Exception e) {
                System.out.println("发送GET请求出现异常！" + e);
                e.printStackTrace();
            } finally {
                try {
                    if (in != null) {
                        in.close();
                    }
                } catch (Exception e2) {
                    e2.printStackTrace();
                }
            }
            return result.toString();
        }

        /**
         * 向指定 URL 发送POST方法的请求
         *
         * @param url   发送请求的URL 例如：http://localhost:8080/demo/login
         * @param param 请求参数 例：{ "userName":"admin", "password":"123456" }
         * @return  所代表远程资源的响应结果
         */
        public static String sendPost(String url, Map<String, Object> param) {
            BufferedReader in = null;
            StringBuilder result = new StringBuilder();
            try {
                URL realUrl = createURL(url, param);
                // 打开和URL之间的连接
                HttpURLConnection conn = (HttpURLConnection) realUrl.openConnection();
                // 发送POST请求必须设置
                conn.setDoOutput(true);
                conn.setDoInput(true);
                conn.setRequestMethod("POST");
                conn.setUseCaches(false);
                conn.setInstanceFollowRedirects(true);
                // 设置通用的请求属性
                conn.setRequestProperty("Charset", "UTF-8");
                conn.setRequestProperty("Content-Type", "application/json; charset=UTF-8");
                conn.connect();
                // 定义BufferedReader输入流来读取URL的响应
                in = new BufferedReader(
                        new InputStreamReader(conn.getInputStream()));
                String line;
                while ((line = in.readLine()) != null) {
                    result.append(line);
                }
            } catch (Exception e) {
                System.out.println("发送 POST 请求出现异常！" + e);
                e.printStackTrace();
            } finally {
                try {
                    if (in != null) {
                        in.close();
                    }
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
            return result.toString();
        }


        private static URL createURL(String url, Map<String, Object> param) throws MalformedURLException {
            if (param == null || param.size() == 0){
                return new URL(url);
            }
            StringBuilder sb = new StringBuilder(url);
            sb.append("?");
            for (String key : param.keySet()) {
                sb.append(key);
                sb.append("=");
                sb.append(encode(String.valueOf( param.get(key))));
                sb.append("&");
            }
            return new URL(sb.substring(0, sb.length() - 1));
        }

        private static String encode(String text) {
            try {
                return URLEncoder.encode(text, "UTF-8");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
            return null;
        }
    }