確定字符串是Java中的絕對URL還是相對URL

Question

給定一個字符串，如何確定它是Java中的絕對URL還是相對URL？ 我嘗試了以下代碼：

private boolean isAbsoluteURL(String urlString)
    {
        boolean result = false;
        try
        {
            URL url = new URL(urlString);
            String protocol = url.getProtocol();
            if (protocol != null && protocol.trim().length() > 0)
                result = true;
        }
        catch (MalformedURLException e)
        {
            return false;
        }
        return result;
    }

問題在於，由於未定義任何協議（例如：www.google.com和/ questions / ask），所有相對URL都拋出MalformedURLException。

Answer 1

怎么樣：

final URI u = new URI("http://www.anigota.com/start");
// URI u = new URI("/works/with/me/too");
// URI u = new URI("/can/../do/./more/../sophis?ticated=stuff+too");

if(u.isAbsolute())
{
  System.out.println("Yes, i am absolute!");
}
else
{
  System.out.println("Ohh noes, it's a relative URI!");
}

有關詳細信息，請參見： http : //docs.oracle.com/javase/7/docs/api/java/net/URI.html

高溫超導

Answer 2

這是我用來確保鏈接是絕對的代碼段：

 private String ensureAbsoluteURL(String base, String maybeRelative) {
    if (maybeRelative.startsWith("http")) {
        return maybeRelative;
    } else {
        try {
           return new URL(new URL(base), maybeRelative).toExternalForm();
        } catch (MalformedURLException e) {
           // do something
        }
    }
}

Answer 3

正如我在評論中所說，您必須先對URL進行規范化，然后再進行檢查，並且規范化取決於您的應用程序，因為www.google.com並非絕對URL。 這是一個示例代碼，可用於檢查URL是否是絕對的：

import java.net.URL;

public class Test {
  public static void main(String [] args) throws Exception {
    String [] urls = {"www.google.com",
                      "http://www.google.com",
                      "/search",
                      "file:/dir/file",
                      "file://localhost/dir/file",
                      "file:///dir/file"};

    for(String url:urls) {
      System.out.println("`" + url + "' is " + 
                          (isAbsoluteURL(url)?"absolute":"relative"));
    }
  }

  public static boolean isAbsoluteURL(String url)
                          throws java.net.MalformedURLException {
    final URL baseHTTP = new URL("http://example.com");
    final URL baseFILE = new URL("file:///");
    URL frelative = new URL(baseFILE, url);
    URL hrelative = new URL(baseHTTP, url);
    System.err.println("DEBUG: file URL: " + frelative.toString());
    System.err.println("DEBUG: http URL: " + hrelative.toString());
    return frelative.equals(hrelative);
  }
}

運行：

~$ java Test 2>/dev/null
`www.google.com' is relative
`http://www.google.com' is absolute
`/search' is relative
`file:/dir/file' is absolute
`file://localhost/dir/file' is absolute
`file:///dir/file' is absolute

Answer 4

我做的

public static String processUrl(String urlToProcess, String grantedNormalUrl){
    if (urlToProcess.startsWith("//")){
        urlToProcess = checkUrlStartsWithProtocol(urlToProcess);
        return urlToProcess;
    }

    if (!isAbsolute(urlToProcess)){
        String rootPage = extractRootPage(grantedNormalUrl);
        boolean domainEndsWithSlash = rootPage.endsWith("/");
        boolean urlStartsWithSlash = urlToProcess.startsWith("/");
        if (domainEndsWithSlash && urlStartsWithSlash){
            rootPage = rootPage.substring(0, rootPage.length() - 1); // exclude /
        }
        urlToProcess = rootPage + (!(domainEndsWithSlash || urlStartsWithSlash) ? "/" : "") + urlToProcess;
    }

    return urlToProcess;
}

public static boolean isAbsolute(String url){
    if (url.startsWith("//")) { // //www.domen.com/start
        return true;
    }

    if (url.startsWith("/")){ // /somePage.html
        return false;
    }

    boolean result = false;

    try {
        URI uri = new URI(url);
        result = uri.isAbsolute();
    } catch (URISyntaxException e) {
        e.printStackTrace();
    }

    return result;
}

public static String checkUrlStartsWithProtocol(String url) {
    if (!url.startsWith("http://") && !url.startsWith("https://")) {
        StringBuilder prefixBuilder = new StringBuilder();
        prefixBuilder.append("http:");
        if (!url.startsWith("//")) {
            prefixBuilder.append("//");
        }
        url = prefixBuilder.toString() + url;
    }
    return url;
}

public static String extractRootPage(String urlString) {
    int ignoreSlashes = 0;
    if (urlString.startsWith("http://") || urlString.startsWith("https://")) {
        ignoreSlashes = 2;
    }
    int endPosition = urlString.length();
    for (int i = 0; i < urlString.length(); i++) {
        if (urlString.charAt(i) == '/') {
            if (ignoreSlashes == 0) {
                endPosition = i; //substring exclude /
                break;
            } else {
                ignoreSlashes--;
            }
        }
    }
    return checkUrlStartsWithProtocol(urlString.substring(0, endPosition));
}