从 java.io.IOException 中提取 HTTP 状态代码

Question

如何（如果有的话）从 java.io.IOException in java 获取 HTTP 状态代码？

Answer 1

我假设这是关于 URLConnection 抛出的 IOException。

根据您的限制，有三种处理方法。

1) 将您的 URLConnection 转换为 HttpURLConnection 并调用 getResponseCode

如果您有权访问连接对象，则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

如果你能做到这一点，那将是最好的解决方案，因为 URLConnection 不会抛出错误状态代码。您可以先调用 getResponseCode 并检查状态而不会出现任何异常。

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

所以您可以只使用正则表达式（或简单的字符串操作）从那里获取响应代码。

请注意，对于状态 404，消息看起来不像这样，会抛出 FileNotFoundException。我不确定是否有任何其他状态代码抛出这样的 "special" 异常，但请注意这一点。

演示方法 2 和 3 的示例代码：

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                                                                                                                                                                                     

-------

从 java.io.IOException 中提取 HTTP 状态代码

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