从java中提取HTTP状态代码。伊奥。IOException

Question

如何从java获取HTTP状态代码（如果有的话）。伊奥。java中的IOException？

Answer 1

我假设这是关于URLConnection引发的IOException。

根据你的限制，有三种可能处理这个问题。

1）将您的URLConnection转换为HttpURLConnection并调用get响应代码

如果您有权访问连接对象，您可以使用此代码获取状态代码：

int statusCode = (HttpURLConnection)theConnection).getResponseCode();

2） 首先使用HttpURLConnection而不是URLConnection

如果您可以做到这一点，这将是最好的解决方案，因为URLConnection不会抛出错误状态代码。您只需调用get响应代码并检查状态，而不会首先获得任何异常。

3） 解析异常消息本身

IOException的消息通常如下所示：

Server returned HTTP response code: 403 for URL: http://something

因此，您可以使用正则表达式（或简单的字符串操作）来获取响应代码。

请注意，对于状态404，消息与此不同，并引发FileNotFoundException。我不确定是否有其他状态码抛出类似的“特殊”异常，但请注意这一点。

示例代码演示方法2

import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class HelloWorld {
    public static void testUrl(String urlString) throws MalformedURLException {
        URLConnection conn = null;
        System.out.println("Testing URL " + urlString);
        try {
            URL url = new URL(urlString);
            conn = url.openConnection();

            // Just to make the exception happen
            conn.getInputStream();

            System.out.println("Success!");
        } catch(IOException ex) {
            System.out.println("Error!");
            System.out.println();

            // Method 2 with access to the URLConnection object
            // (Method 1 would have been having the connection as HttpURLConnection from the beginning.)
            int responseCode = 0;
            System.out.println("Trying method 2 to get status code");

            try {
                if(conn != null) {
                    // Casting to HttpURLConnection allows calling getResponseCode
                    responseCode = ((HttpURLConnection)conn).getResponseCode();
                } else {
                    System.out.println("conn variable not set");
                }
            } catch(IOException ex2) {
                System.out.println("getResponseCode threw: " + ex2);
            }

            System.out.println("Status code from calling getResponseCode: " + responseCode);
            System.out.println();

            // Method 3 without access to the URLConnection object
            responseCode = 0;
            System.out.println("Trying method 3 to get status code");

            // First we try parsing the exception message to see if it contains the response code
            Matcher exMsgStatusCodeMatcher = Pattern.compile("^Server returned HTTP response code: (\\d+)").matcher(ex.getMessage());
            if(exMsgStatusCodeMatcher.find()) {
                responseCode = Integer.parseInt(exMsgStatusCodeMatcher.group(1));
            } else if(ex.getClass().getSimpleName().equals("FileNotFoundException")) {
                // 404 is a special case because it will throw a FileNotFoundException instead of having "404" in the message
                System.out.println("Got a FileNotFoundException");
                responseCode = 404;
            } else {
                // There can be other types of exceptions not handled here
                System.out.println("Exception (" + ex.getClass().getSimpleName() + ") doesn't contain status code: " + ex);
            }

            System.out.println("Status code from parsing exception message: " + responseCode);
            System.out.println();
        }

        System.out.println("-------");
        System.out.println();
    }

    public static void main(String []args) throws MalformedURLException {
        testUrl("https://httpbin.org/status/200");
        testUrl("https://httpbin.org/status/404");
        testUrl("https://httpbin.org/status/403");
        testUrl("http://nonexistingsite1111111.com");
    }
}

示例代码的输出：

Testing URL https://httpbin.org/status/200                                                                                                                                                                                        
Success!                                                                                                                                                                                                                          
-------                                                                                                                                                                                                                           

Testing URL https://httpbin.org/status/404                                                                                                                                                                                        
Error!                                                                                                                                                                                                                            

Trying method 2 to get status code                                                                                                                                                                                                
Status code from calling getResponseCode: 404                                                                                                                                                                                     

Trying method 3 to get status code                                                                                                                                                                                                
Got a FileNotFoundException                                                                                                                                                                                                       
Status code from parsing exception message: 404                                                                                                                                                                                   

-------

Testing URL https://httpbin.org/status/403                                                                                                                                                                                        
Error!                                                                                                                                                                                                                            

Trying method 2 to get status code                                                                                                                                                                                                
Status code from calling getResponseCode: 403                                                                                                                                                                                     

Trying method 3 to get status code                                                                                                                                                                                                
Status code from parsing exception message: 403                                                                                                                                                                                   

-------

Testing URL http://nonexistingsite1111111.com                                                                                                                                                                                     
Error!                                                                                                                                                                                                                            

Trying method 2 to get status code                                                                                                                                                                                                
getResponseCode threw: java.net.UnknownHostException: nonexistingsite1111111.com                                                                                                                                                  
Status code from calling getResponseCode: 0                                                                                                                                                                                       

Trying method 3 to get status code                                                                                                                                                                                                
Exception (UnknownHostException) doesn't contain status code: java.net.UnknownHostException: nonexistingsite1111111.com                                                                                                           
Status code from parsing exception message: 0                                                                                                                                                                                     

-------