假设我有一个完整的文件路径:(/sdcard/tlogo.png)。我想知道它的mime类型。
我为它创建了一个函数
public static String getMimeType(File file, Context context)
{
Uri uri = Uri.fromFile(file);
ContentResolver cR = context.getContentResolver();
MimeTypeMap mime = MimeTypeMap.getSingleton();
String type = mime.getExtensionFromMimeType(cR.getType(uri));
return type;
}
但当我调用它时,它返回null。
File file = new File(filePath);
String fileType=CommonFunctions.getMimeType(file, context);
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;
}
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;
}
}
}