Java 获取文件后缀名

 public String getFileExtension(URL extUrl) {
        String extension="";
        String path = extUrl.getPath();
        String[] pathContents = path.split("[\\\\/]");
        if(pathContents != null){
            int pathContentsLength = pathContents.length;
            String lastPart = pathContents[pathContentsLength-1];
            String[] lastPartContents = lastPart.split("\\.");
            if(lastPartContents != null && lastPartContents.length > 1){
                int lastPartContentLength = lastPartContents.length;
                String name = "";
                for (int i = 0; i < lastPartContentLength; i++) {
                    if(i < (lastPartContents.length -1)){
                        name += lastPartContents[i] ;
                        if(i < (lastPartContentLength -2)){
                            name += ".";
                        }
                    }
                }
                extension = lastPartContents[lastPartContentLength -1];
            }
        }
        return extension;
    }

    public String getFileExtensionByURL(URL url) {

        String trimFile = url.getFile().trim();
        if (trimFile == null || trimFile.equals("") || trimFile.equals("/")) {
            return ".obj";
        }
        int strIndex = trimFile.lastIndexOf("/");
        String filePart = trimFile.substring(strIndex + 1, trimFile.length());
        strIndex = filePart.lastIndexOf(".");
        if (strIndex == -1 || strIndex == filePart.length() - 1) {
            return ".obj";
        } else {
            String fileExt = filePart.substring(strIndex, filePart.length());
            return fileExt;
        }

    }