说明

      进行微信开发，后台程序需要与微信服务器进行交互，通过调用接口来完成服务，阅读微信开发文档，发现接口的调用都是通过http请求进行的，所以必须有个HttpUtil来支撑，这里总结下以javaAPI的方式和以Apach的HttpClient的方式进行HTTP请求

正文

使用java的HttpURLConnection

一个方法实现GET,POST请求

public static String httpRequest(String requestUrl, String requestMethod, String outputStr){
        StringBuffer buffer = new StringBuffer();
        try {
            URL url = new URL(requestUrl);
            HttpURLConnection httpURLConnection = (HttpURLConnection)url.openConnection();
            httpURLConnection.setDoInput(true);
            httpURLConnection.setDoOutput(true);
            httpURLConnection.setUseCaches(false);
            httpURLConnection.setRequestMethod(requestMethod);

            if("GET".equalsIgnoreCase(requestMethod)){
                httpURLConnection.connect();
            }

            if(null != outputStr){
                OutputStream outputStream = httpURLConnection.getOutputStream();
                outputStream.write(outputStr.getBytes("utf-8"));
                outputStream.close();
            }

            InputStream inputStream = httpURLConnection.getInputStream();
            InputStreamReader inputStreamReader = new InputStreamReader(inputStream,"utf-8");
            BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
            String str = null;
            while((str = bufferedReader.readLine())!= null){
                buffer.append(str);
            }

            bufferedReader.close();
            inputStreamReader.close();
            inputStream.close();
            httpURLConnection.disconnect();
        } catch (IOException e) {
            e.printStackTrace();
        }

        return buffer.toString();
    }

此方法通过指定URL,请求的方式和参数进行请求，使用流的方式发送参数和读取响应结果。该方法简单，没有设置http的请求属性等，示例代码在微信开发中可以实现功能。
在此方法中 参数outputStr是向微信服务器发送的json格式的数据或者xml结构的数据，友好性不太好，通常应该传递Map<String,Object> params 保存参数

Get请求

private static final String CHAR_SET = "UTF-8";

 public static String sendGet(String url, Map<String,Object> params){
        StringBuilder responseStr = null;
        StringBuilder paramsStr = new StringBuilder();
        if(params != null || params.size() > 0){
            for(Map.Entry<String,Object> entry : params.entrySet()){
                paramsStr.append(entry.getKey());
                paramsStr.append("=");
                try {
                    paramsStr.append(URLEncoder.encode(String.valueOf(entry.getValue()),CHAR_SET));
                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                }
                paramsStr.append("&");
            }
        }
        URL URLstr = null;
        BufferedReader bufr = null;
        HttpURLConnection httpURLConnection = null;
        try {
            if(paramsStr != null && paramsStr.length() > 0){
                url = url + "?" + paramsStr.substring(0,paramsStr.length() - 1);
            }
            URLstr = new URL(url);
            httpURLConnection = (HttpURLConnection) URLstr.openConnection();
            httpURLConnection.setRequestProperty("Content-Type","application/x-www-form-urlencoded");
            httpURLConnection.connect();
            responseStr = new StringBuilder();
            bufr = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream(),CHAR_SET));
            String str = null;
            while((str = bufr.readLine()) != null){
                responseStr.append(str);
            }
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            httpURLConnection.disconnect();
            if (bufr != null){
                try {
                    bufr.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return  responseStr.toString();
    }

Post请求

public static String sendPost(String url, Map<String, Object> params){
        StringBuilder responseStr = null;
        StringBuilder paramsStr = new StringBuilder();
        if(params != null || params.size() > 0){
            for(Map.Entry<String,Object> entry : params.entrySet()){
                paramsStr.append(entry.getKey());
                paramsStr.append("=");
                try {
                    paramsStr.append(URLEncoder.encode(String.valueOf(entry.getValue()),CHAR_SET));
                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                }
                paramsStr.append("&");
            }
        }
        URL URLstr = null;
        BufferedReader bufr = null;
        HttpURLConnection httpURLConnection = null;
        OutputStreamWriter osw = null;
        try {
            URLstr = new URL(url);
            httpURLConnection = (HttpURLConnection) URLstr.openConnection();
            httpURLConnection.setRequestMethod("POST");
            httpURLConnection.setDoOutput(true);
            httpURLConnection.setDoInput(true);
            httpURLConnection.setUseCaches(false);
            if(paramsStr != null && paramsStr.length() > 0){
                osw = new OutputStreamWriter(httpURLConnection.getOutputStream(),CHAR_SET);
                osw.write(paramsStr.substring(0,paramsStr.length() - 1));
                osw.flush();
            }
            bufr = new BufferedReader(new InputStreamReader(httpURLConnection.getInputStream(),CHAR_SET));
            String str = null;
            while((str = bufr.readLine()) != null){
                responseStr.append(str);
            }

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(osw != null){
                try {
                    osw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if(httpURLConnection != null) {
                httpURLConnection.disconnect();
            }
            if(bufr != null){
                try {
                    bufr.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

        }
        return responseStr.toString();
    }

通过对比sendGet和sendPost两种方法，发现不同之处有：

• 在创建URL对象时，sendGet方法的url是直接拼接了参数，而sendPost方法没有，sendPost方法通过OutputStremWriter对象将参数直接写出
• 在创建了HttpURLConnection对象后，sendGet方法调用了connect()方法，sendPost没有调用此方法，但是显示设置了RequestMethod为POST
• 在设置参数sendGet方法显示设置了“Content-Type”,sendPost则省略了，该参数可以不显示设置，关于“application/x-www-form-urlencoded”详细解释，为什么可以不显示设置，详见：《HTTP中application/x-www-form-urlencoded字符说明》
• 在sendPost方法中显示设置了DoOutput和DoInput为true，UseCaches为false

使用HttpClient

Get请求

public static String httpClienOfGet(String url,Map<String,Object> params){
        String res = "";
        StringBuilder paramsStr = null;
        if(params != null && params.size() > 0){
            for(Map.Entry<String,Object> entry : params.entrySet()){
                paramsStr.append(entry.getKey());
                paramsStr.append("=");
                try {
                    paramsStr.append(URLEncoder.encode(String.valueOf(entry.getValue()),CHAR_SET));
                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                }
                paramsStr.append("&");
            }
        }

        if(paramsStr != null && paramsStr.length() > 0){
            url = url + "?" + paramsStr.substring(0,paramsStr.length() - 1);
        }
        HttpGet httpGet = new HttpGet(url);
        CloseableHttpClient httpClient = HttpClientBuilder.create().build();
        try {
            HttpResponse response = httpClient.execute(httpGet);
            if(response.getStatusLine().getStatusCode() == HttpStatus.SC_OK){
                res = EntityUtils.toString(response.getEntity());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(httpClient != null){
                try {
                    httpClient.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        return res;
    }

Post请求

 public static String httpClientOfPost(String url, Map<String, Object> params){
        String res = "";
        List<NameValuePair> paramList = new ArrayList<NameValuePair>();
        CloseableHttpClient httpClient = HttpClientBuilder.create().build();
        HttpPost  httpPost = new HttpPost(url);

        if(params != null && params.size() > 0){
            for(Map.Entry<String,Object> entry : params.entrySet()){
                paramList.add(new BasicNameValuePair(entry.getKey(),String.valueOf(entry.getValue())));
            }
        }

        try {
            if(paramList.size() > 0){
                UrlEncodedFormEntity urlEncodedFormEntity = new UrlEncodedFormEntity(paramList,CHAR_SET);
                httpPost.setEntity(urlEncodedFormEntity);
            }
            HttpResponse response = httpClient.execute(httpPost);
            if(response.getStatusLine().getStatusCode() == HttpStatus.SC_OK){
                res = EntityUtils.toString(response.getEntity());
            }
        } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }finally {
            if(httpClient != null){
                try {
                    httpClient.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

        return res;
    }

通过比较这两种方式，发现在创建请求方法时，对url处理不同，HttpGet的url直接拼接了参数，而HttpGet的url不做处理，参数则是通过了urlEncodedFormEntity 对象进行设置

通过Post请求发送接收json格式的数据

在微信开发时，通常要通过http发送json格式的数据，微信服务器返回的是json数据，包含了code和msg

public static String jsonOfPost(String url, String param){
        String res = "";
        DefaultHttpClient client = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);
        httpPost.setHeader("Accept","application/json");
        httpPost.setHeader("Content-Type","application/json");
        String charSet = "UTF-8";
        HttpResponse response = null;

        try {
            StringEntity entity = new StringEntity(param,charSet);
            entity.setContentEncoding(charSet);
            entity.setContentType("application/json");
            httpPost.setEntity(entity);
            response = client.execute(httpPost);
            StatusLine statusLine = response.getStatusLine();
            int state = statusLine.getStatusCode();
            if(state == org.apache.http.HttpStatus.SC_OK){
                HttpEntity responseEntity = response.getEntity();
                res = EntityUtils.toString(responseEntity);
                return res;
            }else{
                System.out.println("请求出错");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return res;
    }

关于http的请求总结到这里，有关于POST和GET请求的区别，详见：
https://blog.csdn.net/yaojianyou/article/details/1720913/
http://www.nowamagic.net/librarys/veda/detail/1919

参考的优秀博文：
https://www.cnblogs.com/mengrennwpu/p/6418114.html
https://blog.csdn.net/u010197591/article/details/51441399
https://blog.csdn.net/qq9808/article/details/78320816