java发起http请求

在java中利用jdk提供的方法我们可以很轻松的发起一个http请求。

URL  realURL = new URL(url);  //java.net.URL
URLConnection conn = realURL.openConnection( );
//设置请求头
connection.setRequestProperties("accept","*/*");
conn.setRequestProperty("connection", "Keep-Alive");
conn.setRequestProperty("Content-Type", "application/json");
conn.setRequestProperty("user-agent","Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
// 发送POST请求必须设置如下两行
conn.setDoOutput(true);
conn.setDoInput(true);
 // 获取URLConnection对象对应的输出流
out = new PrintWriter(conn.getOutputStream());
// 发送请求参数
out.print(param);
out.flush();
BufferedReader in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
String line;
String result;
while ((line = in.readLine()) != null) {result += line;}

发起一个post请求

OkHttpClient client = new OkHttpClient.Builder().
    connectTimeout(10, TimeUnit.SECONDS).
    readTimeout(20, TimeUnit.SECONDS).build(); //超时时间设置
MediaType mediaType = MediaType.parse("application/json");
    String url = "request_url";
okhttp3.RequestBody requestBody=okhttp3.RequestBody.
    create(message, mediaType);
Request request = new Request.Builder().url(url).post(requestBody).
addHeader("Content-Type", "application/json").
    addHeader("header", key).build();
try {
        Response response = client.newCall(request).execute();
        response.body().string();
 } catch (IOException e) {
        e.printStackTrace();
 }