依賴jar

        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>2.5</version>
        </dependency>

public static void main(String[] args) {
        //GBK編碼格式原始碼路徑
        String srcDirPath = "D:\\Users\\IdeaWorkSpace\\gitee"
 
;
        //轉為UTF-8編碼格式原始碼路徑
        String utf8DirPath = "D:\\Users\\IdeaWorkSpace\\gitee\\UTF8";
        //獲取所有java檔案
        Collection<File> javaGbkFileCol =  FileUtils.listFiles(new File(srcDirPath), new String[]{"java"}, true);
        for (File javaGbkFile : javaGbkFileCol) {
            //UTF8格式檔案路徑
 

            String utf8FilePath = utf8DirPath+javaGbkFile.getAbsolutePath().substring(srcDirPath.length());
            //使用GBK讀取資料，然後用UTF-8寫入資料
            try {
                FileUtils.writeLines(new File(utf8FilePath), "UTF-8", FileUtils.readLines(javaGbkFile, "GBK"));
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }