java - 如何检查 URL 是否存在或使用 Java 返回 404？

Question

String urlString = "http://www.nbc.com/Heroes/novels/downloads/Heroes_novel_001.pdf";
URL url = new URL(urlString);
if(/* Url does not return 404 */) {
    System.out.println("exists");
} else {
    System.out.println("does not exists");
}
urlString = "http://www.nbc.com/Heroes/novels/downloads/Heroes_novel_190.pdf";
url = new URL(urlString);
if(/* Url does not return 404 */) {
    System.out.println("exists");
} else {
    System.out.println("does not exists");
}

这应该打印出来

exists
does not exists

测试

public static String URL = "http://www.nbc.com/Heroes/novels/downloads/";

public static int getResponseCode(String urlString) throws MalformedURLException, IOException {
    URL u = new URL(urlString); 
    HttpURLConnection huc =  (HttpURLConnection)  u.openConnection(); 
    huc.setRequestMethod("GET"); 
    huc.connect(); 
    return huc.getResponseCode();
}

System.out.println(getResponseCode(URL + "Heroes_novel_001.pdf")); 
System.out.println(getResponseCode(URL + "Heroes_novel_190.pdf"));   
System.out.println(getResponseCode("http://www.example.com")); 
System.out.println(getResponseCode("http://www.example.com/junk"));           

输出

200
200
200
404

解决方案

在 .connect() 之前添加下一行，输出将为 200、404、200、404

huc.setRequestProperty("User-Agent", "Mozilla/5.0 (Windows; U; Windows NT 6.0; en-US; rv:1.9.1.2) Gecko/20090729 Firefox/3.5.2 (.NET CLR 3.5.30729)");

Answer 1

你可能想添加

HttpURLConnection.setFollowRedirects(false);
// note : or
//        huc.setInstanceFollowRedirects(false)

如果你不想跟随重定向 (3XX)

您只需要一个“HEAD”而不是“GET”。

huc.setRequestMethod("HEAD");
return (huc.getResponseCode() == HttpURLConnection.HTTP_OK);