文件操作常用工具方法

写字节到文件：

/**
     * 工具方法，写bytes到文件中 如果写入过程出现异常就删除文件
     * 
     * @param bytes
     * @param file
     */
    public static void writeBytesToFile(byte[] bytes, File file) {
        RandomAccessFile access = null;
        try {
            access = new RandomAccessFile(file, "rw");
            access.write(bytes);
        } catch (IOException e) {
            if (e.getMessage() != null) {
                Log.e("JsonUtil2", e.getMessage());
            }
            file.delete();
        } finally {
            JsonUtil.release(access);
        }
    }

随机读取文件的字节：

/**
     * 工具方法，随机位置读取文件的字节
     * 
     * @param file
     * @param position
     * @param length
     * @return
     */
    public static byte[] readFile(File file, int position, int length) {
        if (file == null || !file.exists() || !file.isFile()) {
            return null;
        }
        RandomAccessFile access = null;
        byte[] bytes = new byte[length];
        try {
            access = new RandomAccessFile(file, "r");
            access.seek(position);
            access.readFully(bytes, 0, length);
            return bytes;
        } catch (Exception e) {
            if (e.getMessage() != null) {
                Log.e("JsonUtil2", e.getMessage());
            }
            return null;
        } finally {
            JsonUtil.release(access);
        }
    }

读取文件的全部字节：

/**
     * 工具方法，读文件的字节
     * 
     * @param file
     * @return
     */
    private static byte[] readFile(File file) {
        if (file == null || !file.isFile() || !file.canRead()) {
            return null;
        }
        FileInputStream fis = null;
        BufferedInputStream bis = null;
        long fileSize = file.length();
        if (fileSize > Integer.MAX_VALUE) {
            System.out.println("file too big...");
            return null;
        }
        ByteArrayOutputStream bos = new ByteArrayOutputStream((int) fileSize);
        try {
            bis = new BufferedInputStream(new FileInputStream(file));
            int buf_size = 1024;
            byte[] buffer = new byte[buf_size];
            int len = 0;
            while (-1 != (len = bis.read(buffer, 0, buf_size))) {
                bos.write(buffer, 0, len);
            }
            return bos.toByteArray();
        } catch (IOException e) {
            Log.e("JsonUtil2", "read bytes form file error");
            return null;
        } finally {
            JsonUtil.release(fis);
            JsonUtil.release(bis);
        }
    }

从文件中读取出字符串：

/**
     * 从给定文件中读出字符串
     * 
     * @param file
     * @return string， null 如果文件不存在
     */
    public static String readFromFile(File file) {
        if (file == null || !file.exists() || !file.isFile()) {
            Log.e("JsonUtil", "cannot read file");
            return null;
        }
        StringBuilder sBuilder = new StringBuilder("");
        FileReader fr = null;
        BufferedReader br = null;
        char[] buffer = new char[1024];
        int length = -1;
        try {
            fr = new FileReader(file);
            br = new BufferedReader(fr);
            while ((length = br.read(buffer)) != -1) {
                sBuilder.append(buffer, 0, length);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            release(fr);
            release(br);
        }
        if (sBuilder.length() == 0) {// 如果读取后长度仍为零
            return null;
        }
        // Log.i("bbbbb", ""+sBuilder.toString());//test
        /**
         * 要判断第一个char是不是utf8 bom文件头 如果是则去掉第一个char
         */
        if (getTHEChar().equals(((Character) (sBuilder.charAt(0))))) {
            sBuilder.deleteCharAt(0);
        }
        return sBuilder.toString();
    }

释放closable资源：

/**
     * 释放closable的资源
     * 
     * @param closeobj
     */
    public static void release(Closeable closeobj) {
        if (closeobj != null) {
            try {
                closeobj.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            closeobj = null;
        }
    }

写字符串到文件：

/**
     * 将指定字符串写入指定文件中,覆盖写
     * 
     * @param file
     * @param str
     * @param cover
     *            是否覆盖写，true 覆盖，false 追加
     */
    private static void writeToFile(File file, String str, Boolean cover) {
        cover = !cover;
        if (file == null || !file.exists() || !file.isFile()) {
            Log.e("JsonUtil", "cannot write file");
            return;
        }
        if (str == null) {
            return;
        }

        FileWriter fw = null;
        BufferedWriter bw = null;

        try {
            fw = new FileWriter(file, cover);
            bw = new BufferedWriter(fw);
            // Log.e("JsonUtil",file.getAbsolutePath());
            bw.write(str);
            bw.flush();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            release(fw);
            release(bw);
        }
    }

 有BOM的utf-8文件头：

/**
     * 得到utf8文件头的char
     * 
     * @return
     */
    private static Character getTHEChar() {
        byte a = (byte) 239;// 0xef(byte)0xef;eb
        byte b = (byte) 187;// (byte)0xbb;bc
        byte c = (byte) 191;// 0xbf;80
        // char ret =
        // (char)(((a&0x000000ff)<<24)|(b&0x000000ff)<<16|(c&0x000000ff)<<8|0x00000000);
        // return (Character)ret;
        char[] chars = getChars(new byte[] { a, b, c });
        return (Character) chars[0];
    }

    /**
     * bytes转chars
     * 
     * @param bytes
     * @return
     */
    private static char[] getChars(byte[] bytes) {
        Charset cs = Charset.forName("UTF-8");
        ByteBuffer bb = ByteBuffer.allocate(bytes.length);
        bb.put(bytes);
        bb.flip();
        CharBuffer cb = cs.decode(bb);
        return cb.array();
    }

 释放closable资源的方法：

/**
     * 释放closable的资源
     * 
     * @param closeobj
     */
    public static void release(Closeable closeobj) {
        if (closeobj != null) {
            try {
                closeobj.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            closeobj = null;
        }
    }