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);

当前回答

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;
    }

其他回答

在kotlin中,这要简单得多。

解决方案1:

fun getMimeType(file: File): String? = 
    MimeTypeMap.getSingleton().getMimeTypeFromExtension(file.extension)

方案二:(文件扩展名函数)

fun File.mimeType(): String? = 
    MimeTypeMap.getSingleton().getMimeTypeFromExtension(this.extension)

首先,你应该考虑调用MimeTypeMap#getMimeTypeFromExtension(),就像这样:

// url = file path or whatever suitable URL you want.
public static String getMimeType(String url) {
    String type = null;
    String extension = MimeTypeMap.getFileExtensionFromUrl(url);
    if (extension != null) {
        type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);
    }
    return type;
}

Jens的回答的优化版本与零安全和回退类型。

@NonNull
static String getMimeType(@NonNull File file) {
    String type = null;
    final String url = file.toString();
    final String extension = MimeTypeMap.getFileExtensionFromUrl(url);
    if (extension != null) {
        type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension.toLowerCase());
    }
    if (type == null) {
        type = "image/*"; // fallback type. You might set it to */*
    }
    return type;
}

重要:getFileExtensionFromUrl()只适用于小写字母!


更新(19.03.2018)

好处:上面的方法是一个不那么冗长的Kotlin扩展函数:

fun File.getMimeType(fallback: String = "image/*"): String {
    return MimeTypeMap.getFileExtensionFromUrl(toString())
            ?.run { MimeTypeMap.getSingleton().getMimeTypeFromExtension(toLowerCase()) }
            ?: fallback // You might set it to */*
}

我也遇到过类似的问题。到目前为止,我知道不同的名字可能会有不同的结果,所以最终得出了这个解决方案。

public String getMimeType(String filePath) {
    String type = null;
    String extension = null;
    int i = filePath.lastIndexOf('.');
    if (i > 0)
        extension = filePath.substring(i+1);
    if (extension != null)
        type = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);
    return type;
}  

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;
    }