https://blog.csdn.net/qq_28430851/article/details/80899294

import java.io.*;

import java.util.ArrayList;

import java.util.List;

/**

 * utf-8有bom 批量轉(zhuǎn)為 utf-8無bom 文件格式

 */

public class UTF8BOMConverter extends Reader {

    private static final int BOM_SIZE = 4;

    PushbackInputStream internalIn;//回退流對象

    InputStreamReader internalIn2 = null;

    String defaultEnc;//格式

    /**

     * @param in         inputstream to be read

     * @param defaultEnc default encoding if stream does not have

     *                   BOM marker. Give NULL to use system-level default.

     */

    UTF8BOMConverter(InputStream in, String defaultEnc) {

        internalIn = new PushbackInputStream(in, BOM_SIZE);

        this.defaultEnc = defaultEnc;

    }

    private static void readContentAndSaveWithEncoding(String filePath, String readEncoding, String saveEncoding) throws Exception {

        saveContent(filePath, readContent(filePath, readEncoding), saveEncoding);

    }

    private static void saveContent(String filePath, String content, String encoding) throws Exception {

        FileOutputStream fos = new FileOutputStream(filePath);

        OutputStreamWriter w = new OutputStreamWriter(fos, encoding);

        w.write(content);

        w.flush();

    }

    private static String readContent(String filePath, String encoding) throws Exception {

        FileInputStream file = new FileInputStream(new File(filePath));

        BufferedReader br = new BufferedReader(new UTF8BOMConverter(file, encoding));

        String line = null;

        String fileContent = "";

        while ((line = br.readLine()) != null) {

            fileContent = fileContent + line;

            fileContent += "\r\n";

        }

        return fileContent;

    }

    private static List<String> getPerlineFileName(String filePath) throws Exception {

        FileInputStream file = new FileInputStream(new File(filePath));

        BufferedReader br = new BufferedReader(new InputStreamReader(file, "UTF-8"));

        String line = null;

        List<String> list = new ArrayList<String>();

        while ((line = br.readLine()) != null) {

            list.add(line);

        }

        return list;

    }

    /**

     * 獲取某個(gè)目錄下所有的文件路徑

     * 使用遞歸

     * @param filePath

     * @param filePaths

     * @return

     */

    private static List<String> getAllFilePaths(File filePath, List<String> filePaths) {

        File[] files = filePath.listFiles();

        if (files == null) {

            return filePaths;

        }

        for (File f : files) {

            if (f.isDirectory()) {

                filePaths.add(f.getPath());

                getAllFilePaths(f, filePaths);

            } else {

                filePaths.add(f.getPath());

            }

        }

        return filePaths;

    }

    public static void main(String[] args) throws Exception {

        String suffix = ".java";

        List<String> paths = new ArrayList<String>();

        paths = getAllFilePaths(new File("D:/work/idea_coding/HJMJX/HJMJX/core/src/main/java"), paths);

        List<String> pathList = new ArrayList<String>();

        for (String path : paths) {

            if (path.endsWith(suffix)) {

                pathList.add(path);

            }

        }

        for (String path : pathList) {

            readContentAndSaveWithEncoding(path, "UTF-8", "UTF-8");

            System.out.println(path + "轉(zhuǎn)換成功");

        }

    }

    public String getDefaultEncoding() {

        return defaultEnc;

    }

    /**

     * Get stream encoding or NULL if stream is uninitialized.

     * Call init() or read() method to initialize it.

     */

    public String getEncoding() {

        if (internalIn2 == null) return null;

        return internalIn2.getEncoding();

    }

    /**

     * Read-ahead four bytes and check for BOM marks. Extra bytes are

     * unread back to the stream, only BOM bytes are skipped.

     */

    protected void init() throws IOException {

        if (internalIn2 != null) return;

        String encoding;

        byte bom[] = new byte[BOM_SIZE];

        int n, unread;

        n = internalIn.read(bom, 0, bom.length);

        if ((bom[0] == (byte) 0x00) && (bom[1] == (byte) 0x00) &&

        (bom[2] == (byte) 0xFE) && (bom[3] == (byte) 0xFF)) {

            encoding = "UTF-32BE";

            unread = n - 4;

        } else if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE) &&

        (bom[2] == (byte) 0x00) && (bom[3] == (byte) 0x00)) {

            encoding = "UTF-32LE";

            unread = n - 4;

        } else if ((bom[0] == (byte) 0xEF) && (bom[1] == (byte) 0xBB) &&

        (bom[2] == (byte) 0xBF)) {

            encoding = "UTF-8";

            unread = n - 3;

        } else if ((bom[0] == (byte) 0xFE) && (bom[1] == (byte) 0xFF)) {

            encoding = "UTF-16BE";

            unread = n - 2;

        } else if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)) {

            encoding = "UTF-16LE";

            unread = n - 2;

        } else {

            // Unicode BOM mark not found, unread all bytes

            encoding = defaultEnc;

            unread = n;

        }

        //System.out.println("read=" + n + ", unread=" + unread);

        if (unread > 0) internalIn.unread(bom, (n - unread), unread);

        // Use given encoding

        if (encoding == null) {

            internalIn2 = new InputStreamReader(internalIn);

        } else {

            internalIn2 = new InputStreamReader(internalIn, encoding);

        }

    }

    public void close() throws IOException {

        init();

        internalIn2.close();

    }

    public int read(char[] cbuf, int off, int len) throws IOException {

        init();

        return internalIn2.read(cbuf, off, len);

    }

}