Java获取文件真实格式

需求

很多时候，文件的类型和后缀名不一致，这样就不能简单的用后缀名判断文件的格式。
例如：POI导入excel只能支持.xls和.xlsx的文件解析，但有些真实格式为csv或html的.xls文件混入其中就会导致导入失败，那么就需要根据头部信息匹配格式

获取文件真实类型

1. 获取文件的头部字节
2. 将头部字节转换成16进制字符串
3. 匹配字符串获取文件类型

FileTypeJudge.java

/**
 * 文件类型判断类
 */
public final class FileTypeJudge {

    /**
     * Constructor
     */
    private FileTypeJudge() {}

    /**
     * 将文件头转换成16进制字符串
     */
    private static String bytesToHexString(byte[] src){

        StringBuilder stringBuilder = new StringBuilder();
        if (src == null || src.length <= 0) {
            return null;
        }
        for (byte b : src) {
            int v = b & 0xFF;
            String hv = Integer.toHexString(v);
            if (hv.length() < 2) {
                stringBuilder.append(0);
            }
            stringBuilder.append(hv);
        }
        return stringBuilder.toString();
    }

    /**
     * 得到文件头
     */
    private static String getFileContent(InputStream inputStream) throws IOException {

        byte[] b = new byte[28];

        try {
            inputStream.read(b, 0, 28);
        } finally {
            if (inputStream != null) {
                inputStream.close();
            }
        }
        return bytesToHexString(b);
    }

    /**
     * 判断文件类型
     */
    public static FileType getType(InputStream inputStream) throws IOException {

        String fileHead = getFileContent(inputStream);

        if (fileHead == null || fileHead.length() == 0) {
            return null;
        }

        for (FileType type : FileType.values()) {
            if (fileHead.startsWith(type.code)) {
                return type;
            }
        }

        return null;
    }

    /**
     * InputStream转ByteArrayOutputStream，用于流的复制
     */
    public static ByteArrayOutputStream cloneInputStream(InputStream input) throws IOException {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        int len;
        while ((len = input.read(buffer)) > -1) {
            baos.write(buffer, 0, len);
        }
        baos.flush();
        return baos;
    }
}

关于流的复制

由于判断文件格式需要读取流的头部信息，这个读取是不可逆的，而判断完文件格式后通常还需要读文件，所以需要复制一个InputStream

复制InputStream

InputStream fis = request.getFile("file").getInputStream();
ByteArrayOutputStream temp = cloneInputStream(fis);

// 打开两个新的输入流，一个用于判断文件类型，还有一个用于读取文件内容
InputStream stream1 = new ByteArrayInputStream(temp.toByteArray());
InputStream stream2 = new ByteArrayInputStream(temp.toByteArray());

文件类型枚举

罗列了大部分文件格式的头部信息，如果有新的格式可以测试后添加进去

FileType.java

/**
 * 文件类型枚取
 */
public enum FileType {

    /**
     * JPEG(jpg)
     */
    JPG("ffd8ffe000104a464946","jpg"),
    /**
     * PNG(png)
     */
    PNG("89504e470d0a1a0a0000","png"),
    /**
     * GIF(gif)
     */
    GIF("47494638396126026f01","gif"),
    /**
     * TIFF(tif)
     */
    TIF("49492a00227105008037","tif"),
    /**
     * 16色位图(bmp)
     */
    BMP_16("424d228c010000000000","bmp"),
    /**
     * 24位位图(bmp)
     */
    BMP_24("424d8240090000000000","bmp"),
    /**
     * 256色位图(bmp)
     */
    BMP_256("424d8e1b030000000000","bmp"),
    /**
     * CAD(dwg)
     */
    DWG("41433130313500000000","dwg"),
    /**
     * HTML(html)
     */
    HTML("3c21444f435459504520","html"),
    /**
     * HTM(htm)
     */
    HTM("3c21646f637479706520","htm"),
    /**
     * 猎聘、智联简历。htm
     */
    HTM_2("3c68746d6c20786d6c6e","htm"),
    /**
     * css
     */
    CSS("48544d4c207b0d0a0942","css"),
    /**
     * js
     */
    JS("696b2e71623d696b2e71","js"),
    /**
     * RichTextFormat(rtf)
     */
    RTF("7b5c727466315c616e73","rtf"),
    /**
     * Photoshop(psd)
     */
    PSD("38425053000100000000","psd"),
    /**
     * Email[OutlookExpress6](eml)
     */
    EML("46726f6d3a203d3f6762","eml"),
    /**
     * MSExcel注意：word、msi和excel的文件头一样
     */
    DOC("d0cf11e0a1b11ae10000","doc"),
    /**
     * docx文件
     */
    DOCX("504b0304140006000800","docx"),
    /**
     * MSAccess(mdb)
     */
    MDB("5374616E64617264204A","mdb"),
    PS("252150532D41646F6265","ps"),
    /**
     * AdobeAcrobat(pdf)
     */
    PDF("255044462d312e350d0a","pdf"),
    /**
     * rmvb/rm相同
     */
    RMVB("2e524d46000000120001","rmvb"),
    /**
     * flv与f4v相同
     */
    FLV("464c5601050000000900","flv"),
    MP4("00000020667479706d70","mp4"),
    MP3("49443303000000002176","mp3"),
    /**
     *
     */
    MPG("000001ba210001000180","mpg"),
    /**
     * wmv与asf相同
     */
    WMV("3026b2758e66cf11a6d9","wmv"),
    /**
     * Wave(wav)
     */
    WAV("52494646e27807005741","wav"),
    AVI("52494646d07d60074156","avi"),
    /**
     * MIDI(mid)
     */
    MID("4d546864000000060001","mid"),
    ZIP("504b0304140000000800","zip"),
    RAR("526172211a0700cf9073","rar"),
    INI("235468697320636f6e66","ini"),
    JAR("504b03040a0000000000","jar"),
    /**
     * 可执行文件
     */
    EXE("4d5a9000030000000400","exe"),
    /**
     * jsp文件
     */
    JSP("3c25402070616765206c","jsp"),
    /**
     * MF文件
     */
    MF("4d616e69666573742d56","mf"),
    /**
     * xml文件
     */
    XML("3c3f786d6c2076657273","xml"),
    /**
     * sql文件
     */
    SQL("494e5345525420494e54","sql"),
    /**
     * java文件
     */
    JAVA("7061636b616765207765","java"),
    /**
     * bat文件
     */
    BAT("406563686f206f66660d","bat"),
    /**
     * gz文件
     */
    GZ("1f8b0800000000000000","gz"),
    /**
     * bat文件
     */
    PROPERTIES("6c6f67346a2e726f6f74","properties"),
    /**
     * bat文件
     */
    CLASS("cafebabe0000002e0041","class"),
    /**
     * bat文件
     */
    CHM("49545346030000006000","chm"),
    /**
     * bat文件
     */
    MXP("04000000010000001300","mxp"),
    TORRENT("6431303a637265617465","torrent"),
    /**
     * 51job简历。mht
     */
    MHT("46726f6d3a3cd3c920cd","mht"),
    /**
     * Quicktime(mov)
     */
    MOV("6D6F6F76","mov"),
    /**
     * WordPerfect(wpd)
     */
    WPD("FF575043","wpd"),
    /**
     * OutlookExpress(dbx)
     */
    DBX("CFAD12FEC5FD746F","dbx"),
    /**
     * Outlook(pst)
     */
    PST("2142444E","pst"),
    /**
     * Quicken(qdf)
     */
    QDF("AC9EBD8F","qdf"),
    /**
     * WindowsPassword(pwl)
     */
    PWL("E3828596","pwl"),
    /**
     * RealAudio(ram)
     */
    RAM("2E7261FD","ram");

    public String code;
    public String name;

    FileType(String code, String name) {
        this.code = code;
        this.name = name;
    }
}