com.discovery.darchrow.io.MimeTypeUtil.java Source code

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Here is the source code for com.discovery.darchrow.io.MimeTypeUtil.java

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/*
 * Copyright (C) 2008 feilong
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.discovery.darchrow.io;

import java.net.FileNameMap;
import java.net.URLConnection;
import java.util.HashMap;
import java.util.Map;

import org.apache.commons.io.FilenameUtils;

import com.discovery.darchrow.util.Validator;

/**
 * ?Mime-Type.
 * <p>
 * MIME(Multi-Purpose Internet Mail Extensions)
 *
 * @author feilong
 * @version 1.0.8 20141119 ?1:12:50
 * @see com.baozun.nebulaplus.io.MimeType
 * @see "org.apache.catalina.startup.Tomcat#DEFAULT_MIME_MAPPINGS"
 * @see "org.apache.http.entity.ContentType"
 * @see <a href="http://stackoverflow.com/questions/4348810/java-library-to-find-the-mime-type-from-file-content/10140531#10140531">java
 *      library to find the mime type from file content</a>
 * @see <a href="http://stackoverflow.com/questions/51438/getting-a-files-mime-type-in-java">Getting A File Mime Type In Java</a>
 * @see <a href="http://en.wikipedia.org/wiki/MIME">MIME Wiki</a>
 * @see <a href="http://tika.apache.org/">?Apache Tika</a>
 * @since 1.0.8
 */
public final class MimeTypeUtil {

    /** The Constant fileExtensionMap. */
    private static final Map<String, String> fileExtensionMap;

    /** Don't let anyone instantiate this class. */
    private MimeTypeUtil() {
        //AssertionError?. ?????. ???.
        //see Effective Java 2nd
        throw new AssertionError("No " + getClass().getName() + " instances for you!");
    }

    static {
        fileExtensionMap = new HashMap<String, String>();
        for (MimeType mimeType : MimeType.values()) {
            fileExtensionMap.put(mimeType.getExtension(), mimeType.getMime());
        }
    }

    /**
     *  content type by file name.<br>
     * 
     * //TODO
     * <b>
     * Very incomplete function. As of Java 7, html, pdf and jpeg extensions return the correct mime-type but js and css return null! </b> <br>
     * 
     * <p>
     * I tried Apache Tika but it is huge with tons of dependencies, <br>
     * URLConnection doesn't use the bytes of the files, <br>
     * MimetypesFileTypeMap also just looks at files names,<br>
     * and I couldn't move to Java 7.
     * </p>
     * 
     * @param fileName
     *            the file name
     * @return the content type by file name
     * @see java.net.URLConnection#getFileNameMap()
     * @see javax.activation.MimetypesFileTypeMap#getContentType(java.io.File)
     * @see java.net.FileNameMap#getContentTypeFor(String)
     * @see org.apache.commons.io.FilenameUtils#getExtension(String)
     * @see java.net.URLConnection#guessContentTypeFromName(String)
     * @see java.net.URLConnection#guessContentTypeFromStream(java.io.InputStream)
     * @see "java.nio.file.Files#probeContentType(java.nio.file.Path)"
     */
    public static String getContentTypeByFileName(String fileName) {

        String extension = FilenameUtils.getExtension(fileName);
        if (Validator.isNullOrEmpty(extension)) {
            return null;
        }

        // 1. first use java's build-in utils
        //??? mimetable? "content.types.user.table" ?? java  lib/content-types.properties 
        FileNameMap fileNameMap = URLConnection.getFileNameMap();
        String contentType = fileNameMap.getContentTypeFor(fileName);

        // 2. nothing found -> lookup our in extension map to find types like ".doc" or ".docx"
        if (Validator.isNullOrEmpty(contentType)) {
            contentType = fileExtensionMap.get(extension.toLowerCase());
        }

        return contentType;
    }
}