你有多种选择来获得文件扩展名: 字符串文件名= uri.getLastPathSegment();请看这个链接

2-你也可以使用这段代码

 filePath .substring(filePath.lastIndexOf(".")+1);

但这不是一个好方法。 3-如果你有文件的URI，那么使用这个代码

String[] projection = { MediaStore.MediaColumns.DATA,
MediaStore.MediaColumns.MIME_TYPE };

4-如果你有URL，那么使用下面的代码:

 public static String getMimeType(String url) {
String type = null;
String extension = MimeTypeMap.getFileExtensionFromUrl(url);
if (extension != null) { 


  type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);
    }

return type;
}

享受你的代码:)

I don't realize why MimeTypeMap.getFileExtensionFromUrl() has problems with spaces and some other characters, that returns "", but I just wrote this method to change the file name to an admit-able one. It's just playing with Strings. However, It kind of works. Through the method, the spaces existing in the file name is turned into a desirable character (which, here, is "x") via replaceAll(" ", "x") and other unsuitable characters are turned into a suitable one via URLEncoder. so the usage (according to the codes presented in the question and the selected answer) should be something like getMimeType(reviseUrl(url)).

private String reviseUrl(String url) {

        String revisedUrl = "";
        int fileNameBeginning = url.lastIndexOf("/");
        int fileNameEnding = url.lastIndexOf(".");

        String cutFileNameFromUrl = url.substring(fileNameBeginning + 1, fileNameEnding).replaceAll(" ", "x");

        revisedUrl = url.
                substring(0, fileNameBeginning + 1) +
                java.net.URLEncoder.encode(cutFileNameFromUrl) +
                url.substring(fileNameEnding, url.length());

        return revisedUrl;
    }

以下是我在我的Android应用程序中使用的解决方案:

public static String getMimeType(String url)
    {
        String extension = url.substring(url.lastIndexOf("."));
        String mimeTypeMap = MimeTypeMap.getFileExtensionFromUrl(extension);
        String mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(mimeTypeMap);
        return mimeType;
    }

我尝试使用标准方法来确定mime类型，但我不能使用MimeTypeMap.getFileExtensionFromUrl(uri.getPath())保留文件扩展名。这个方法返回一个空字符串。所以我做了一个重要的解决方案来保留文件扩展名。

下面是返回文件扩展名的方法:

private String getExtension(String fileName){
    char[] arrayOfFilename = fileName.toCharArray();
    for(int i = arrayOfFilename.length-1; i > 0; i--){
        if(arrayOfFilename[i] == '.'){
            return fileName.substring(i+1, fileName.length());
        }
    }
    return "";
}

并且保留了文件扩展名，可以获得如下所示的mime类型:

public String getMimeType(File file) {
    String mimeType = "";
    String extension = getExtension(file.getName());
    if (MimeTypeMap.getSingleton().hasExtension(extension)) {
        mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);
    }
    return mimeType;
}

这里没有一个答案是完美的。以下是一个结合了所有热门答案的最佳元素的答案:

public final class FileUtil {

    // By default, Android doesn't provide support for JSON
    public static final String MIME_TYPE_JSON = "application/json";

    @Nullable
    public static String getMimeType(@NonNull Context context, @NonNull Uri uri) {

        String mimeType = null;
        if (uri.getScheme().equals(ContentResolver.SCHEME_CONTENT)) {
            ContentResolver cr = context.getContentResolver();
            mimeType = cr.getType(uri);
        } else {
            String fileExtension = getExtension(uri.toString());

            if(fileExtension == null){
                return null;
            }

            mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(
                    fileExtension.toLowerCase());

            if(mimeType == null){
                // Handle the misc file extensions
                return handleMiscFileExtensions(fileExtension);
            }
        }
        return mimeType;
    }

    @Nullable
    private static String getExtension(@Nullable String fileName){

        if(fileName == null || TextUtils.isEmpty(fileName)){
            return null;
        }

        char[] arrayOfFilename = fileName.toCharArray();
        for(int i = arrayOfFilename.length-1; i > 0; i--){
            if(arrayOfFilename[i] == '.'){
                return fileName.substring(i+1, fileName.length());
            }
        }
        return null;
    }

    @Nullable
    private static String handleMiscFileExtensions(@NonNull String extension){

        if(extension.equals("json")){
            return MIME_TYPE_JSON;
        }
        else{
            return null;
        }
    }
}

我认为最简单的方法是引用这个资源文件: https://android.googlesource.com/platform/libcore/+/master/luni/src/main/java/libcore/net/android.mime.types