Http连接笔记

常见的Http连接方式介绍。

1、HttpURLConnection

HttpURLConnection继承自最原始的URLConnection，是jdk自带的标准类，无需下载其他jar包。 如果接口响应码被服务端修改则无法接收到返回报文，只能当响应码正确时才能接收到返回 HttpURLConnection方式调用。缺点：无连接池

//ms超时毫秒,url地址,json入参
public static String httpJson(int ms,String url,String json) throws Exception{
        String err = "00", line = null;
        StringBuilder sb = new StringBuilder();
        HttpURLConnection conn = null;
        BufferedWriter out = null;
        BufferedReader in = null;
        try{
                conn = (HttpURLConnection) (new URL(url.replaceAll("／","/"))).openConnection();
                conn.setRequestMethod("POST");
                conn.setDoOutput(true);
                conn.setDoInput(true);
                conn.setUseCaches(false);
                conn.setConnectTimeout(ms);
                conn.setReadTimeout(ms);
                conn.setRequestProperty("Content-Type","application/json;charset=utf-8");
                conn.connect();//建立连接
                out = new BufferedWriter(new OutputStreamWriter(conn.getOutputStream(),"utf-8"));
                out.write(new String(json.getBytes(), "utf-8"));
                out.flush();//发送参数
                int code = conn.getResponseCode();//此时才真正发送请求
                if (conn.getResponseCode()==200){//响应码正确时才继续处理
                        in = new BufferedReader(new InputStreamReader(conn.getInputStream(),"UTF-8"));
                        while ((line=in.readLine())!=null)
                                sb.append(line);
                }//接收返回值
                …
        }

2、Java.net.http.HttpClient

jdk11自带的HttpClient,代替HttpURLConnection

3、Apache HttpClient

需引入jar包，支持连接池。只用关注于如何发请求，接收响应，以及管理HTTP连接。

CloseableHttpClient：HttpClient4.3以上版本支持CloseableHttpClient。

public static String httpPostJson(String url,String json) throws Exception{
        String data=""; 
        CloseableHttpClient httpClient = null;
        CloseableHttpResponse response = null;
        try {
                httpClient = HttpClients.createDefault();//1、创建连接
                HttpPost httppost = new HttpPost(url);//2、创建Http请求对象
        httppost.setHeader("Content-Type", "application/json;charset=UTF-8");
        StringEntity se = new StringEntity(json,Charset.forName("UTF-8"));
                se.setContentType("text/json");
                se.setContentEncoding("UTF-8");
                httppost.setEntity(se);
                response = httpClient.execute(httppost);//3、调用execute方法执行请求
                …
        }

HttpClient与CloseableHttpClient对比：httpclient是一个线程安全的类，没有必要由每个线程在每次使用时创建，全局保留一个即可。ClosableHttpClient默认会创建一个大小为5的连接池，CloseableHttpClient实现了Closeable接口，可以自动关闭资源，不需要在手动关闭资源了

4、okHttp

不需要手动关闭，支持http2 okHttp：

private OkHttpClient client = new OkHttpClient();//1、创建连接
@Test
public void testPost() throws IOException {
    String api = "/api/user";
    String url = String.format("%s%s", BASE_URL, api);
    //请求参数
    JSONObject json = new JSONObject();
    json.put("name", "hetiantian");
    RequestBody requestBody = RequestBody.create(MediaType.parse("application/json; charset=utf-8"),     String.valueOf(json));
    Request request = new Request.Builder()//2、创建Request对象
            .url(url)
            .post(requestBody) //post请求
           .build();
    final Call call = client.newCall(request);//3、将Request 对象封装为Call
    Response response = call.execute();//4、通过Call 来调用execute方法执行
    System.out.println(response.body().string());
}

下面介绍微服务中的使用

1、RestTemplate spring提供的用于访问Rest服务的，底层使用HttpURLConnection，无连接池

2、Openfeign：远程调用