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📜  Java Java类

📅  最后修改于: 2022-05-13 01:55:16.125000             🧑  作者: Mango

Java Java类

HttpURLConnection 类是直接从 URLConnection 类扩展而来的抽象类。它包括其父类的所有功能以及额外的 HTTP 特定功能。 HttpsURLConnection 是另一个用于更安全的 HTTPS 协议的类。

它是Java开发人员与 Web 服务器交互的流行选择之一，android 开发团队已正式建议尽可能使用它。稍后我们将说明一个交互式应用程序的简单实现，该应用程序使用 Microsoft 情感 API 使用 HttpURLConnection 类的方法从图像中检索情感分数。

构造函数

  • HttpURLConnection(URL u)：构造到指定 URL 的 httpurl 连接

方法（除了在 URLConnection 类中）

MethodAction performed
disconnect()Indicated that requests to the server are highly unlikely in the future. 
getErrorStream()Gets the error stream if the server cannot be connected or some error occurred. It can contain information about how to fix the error from the server.
getFollowRedirects()Returns true or false depending on automatic redirection or not.
getHeaderField()Returns the nth header field, or null if it does not exist. It overrides the getHeaderField method of URLConnection class.
getInstanceFollowRedirects()Returns true or false depending on whether automatic instance redirection is set or not.
getPermission()Retrieves the permission required to connect to a destination host and port.
getResponseCode()Used to retrieve the response status from server.
getResponseMessage()Retrieves the response message.
getRequestMethod()Returns the request method.
setInstanceFollowRedirects()Sets whether response code requests be redirected automatically by this instance of HTTP URL connection. It overrides the more generic setFollowRedirects()
setRequestMethod()Used to set the request method. Default is GET
setFixedLengthStreamingMode()Used to set the length of content written on outputstream if it is known in advance.
setFollowRedirects()Sets whether a 3xx response code request be redirected automatically or not.
setChunkedStreamingMode()Used when the content length is not known. Instead of creating a buffer of fixed length and writing it to a server, content is broken into chunks and then written. Not all servers support this mode. 
usingProxy()Returns true if connection is established using a proxy, else false

图解：整个过程可以概括如下：

使用以下 URL 连接到 Microsoft 情感 API 的服务器

https://westus.api.cognitive.microsoft.com/emotion/v1.0/recognize

设置触发请求的属性和方法：在这一步中，我们设置请求对象的方法和属性。首先，我们将该方法设置为请求方法，以 POST 方式调用。我们还设置了 User-Agent 属性，以确保我们的请求不会因为意外的响应类型而被服务器阻止，否则在任何 Web 浏览器上都可以正常工作。

触发 http get 请求：在我们创建了 URL 并创建了一个 HttpURLConnection 对象之后，我们必须实际触发一个请求。它可以通过 connect() 方法显式完成。每当我们尝试使用任何响应消息（例如 getOutputStream() 等）时，它都会隐含地完成。

写入服务器：一旦我们获得到服务器的输出流，我们就将我们的图像上传到服务器进行处理。

从服务器读取响应：获取输入流后，我们使用缓冲读取器从服务器输出结果。

执行：

Java
// Java Program to Illustrate Use
// of HttpURLConnection Class
// to Retrieve Emotion score of Image
// Using Microsoft Emotion API
 
// Importing required classes
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import org.json.simple.JSONObject;
 
// Main class
// httpconclass class
public class GFG {
 
    // Main driver method
    public static void main(String args[])
        throws IOException
    {
 
        // Reading input via BufferedReader class
        BufferedReader br = new BufferedReader(
            new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        String key = "833921b016964f95905442e0fab0c229";
        JSONObject ezm;
 
        while (n-- > 0) {
            String image = br.readLine();
            ezm = new JSONObject();
            ezm.put("url", image);
 
            // Try block to check for exceptions
            try {
 
                // URL for microsoft cognitive server.
                URL url = new URL(
                    "https://westus.api.cognitive.microsoft.com/emotion/v1.0/recognize");
                HttpURLConnection con
                    = (HttpURLConnection)
                          url.openConnection();
 
                // Setting the request method and
                // properties.
                con.setRequestMethod("POST");
                con.setRequestProperty(
                    "Ocp-Apim-Subscription-Key", key);
                con.setRequestProperty("Content-Type",
                                       "application/json");
                con.setRequestProperty("Accept",
                                       "application/json");
 
                // As we know the length of our content,
                // the following function sets the fixed
                // streaming mode length 83 bytes. If
                // content length not known, comment the
                // below line.
                con.setFixedLengthStreamingMode(83);
 
                // Setting the auto redirection to true
                HttpURLConnection.setFollowRedirects(true);
 
                // Overriding the default value set by
                // the static method setFollowRedirect above
                con.setInstanceFollowRedirects(false);
 
                // Setting the doOutput to true for now
                con.setDoOutput(true);
 
                OutputStream out = con.getOutputStream();
                // System.out.println(ezm.toString().getBytes().length);
 
                // Writing on the output stream
                out.write(ezm.toString().getBytes());
                InputStream ip = con.getInputStream();
 
                BufferedReader br1 = new BufferedReader(
                    new InputStreamReader(ip));
 
                // Printing the response code
                // and response message from server.
                System.out.println("Response Code:"
                                   + con.getResponseCode());
                System.out.println(
                    "Response Message:"
                    + con.getResponseMessage());
 
                // Note: Uncomment the following line to
                // print the status of FollowRedirect
                // property
                // System.out.println("FollowRedirects:"
                //           +
                //           HttpURLConnection.getFollowRedirects());
 
                // Printing the status of
                // instanceFollowRedirect property
                System.out.println(
                    "InstanceFollowRedirects:"
                    + con.getInstanceFollowRedirects());
 
                // Printing the 1st header field
                System.out.println("Header field 1:"
                                   + con.getHeaderField(1));
 
                // Printing if usingProxy flag set or not
                System.out.println("Using proxy:"
                                   + con.usingProxy());
 
                StringBuilder response
                    = new StringBuilder();
                String responseSingle = null;
 
                while ((responseSingle = br1.readLine())
                       != null) {
                    response.append(responseSingle);
                }
                String xx = response.toString();
                System.out.println(xx);
            }
 
            // Catch block to handle exceptions
            catch (Exception e) {
               
                // Display exception/s on console
                System.out.println(e.getMessage());
            }
        }
    }
}

输出： 

Response Code:200
Response Message:OK
FollowRedirects:true
InstanceFollowRedirects:false
Header field 1:no-cache
Using proxy:false
[{"faceRectangle":{"height":134,"left":62,"top":86,"width":134},"scores":{"anger":4.105452E-
14,"contempt":1.240792E-11,"disgust":2.58925052E-11,"fear":1.82401266E-17,"happiness":1.0,
"neutral":2.487733E-10,"sadness":6.02089044E-14,"surprise":2.665974E-12}}]

输出说明：要测试此程序，应提供要处理的图像数量，然后提供图像的 URL。您可以不设置内容长度属性，因为服务器会自动处理它，但如果您知道长度，则每次都相应地修改它。在给定的源代码中，由于内容长度设置为 83 字节，因此应使用该大小的 URL。 

Sample URL: https://media.geeksforgeeks.org/wp-content/uploads/Brad_Pitt.jpg