Extract HTTP Status Code from java.io.IOException

Question

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

Answer 1

I'm assuming this is about an IOException thrown by a URLConnection .

Three possibilities to handle this, depending on your restrictions.

1) Cast your URLConnection to a HttpURLConnection and call getResponseCode

If you have access to the connection object, you can get the status code using this code:

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

2) Use a HttpURLConnection instead of an URLConnection in the first place

If you can do this, it would be the best solution, because an URLConnection doesn't throw on error status codes. You can just call getResponseCode and check the status without getting any exception first.

3) Parse the exception message itself

The IOException 's message usually looks like this:

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

So you can just use a regex (or simple string manipulation) to get the response code out of there.

Note that for status 404, the message doesn't look like this and a FileNotFoundException is thrown. I'm not sure if there are any other status codes throwing "special" exceptions like this, but watch out for this.

Example code demonstrating methods 2 & 3:

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");
    }
}

Output of the example code:

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                                                                                                                                                                                     

-------