Java IO流共涉及40多个类，但基类只有四个：

• InputStream / Reader ：所有输入流的基类，前者是字节输入流，后者是字符输 入流。
• OutputStream / Writer ：所有输出流的基类，前者是字节输出流，后者是字符输出 流。

BufferedReader整行读取

public static String readFile(String filename) {
    File file = new File(filename);
    InputStream is = null;
    Reader reader = null;
    BufferedReader bufferedReader = null;
    StringBuilder result = new StringBuilder();
    try {
        is = new FileInputStream(file);
        reader = new InputStreamReader(is);
        bufferedReader = new BufferedReader(reader);
        String line;
        while ((line = bufferedReader.readLine()) != null) {
            result.append(line);
            result.append("\r\n");
        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (null != bufferedReader)
                bufferedReader.close();
            if (null != reader)
                reader.close();
            if (null != is)
                is.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return result.toString();
}

InputStream字节读取

public static String readFileByChar(String filename) {
    File file = new File(filename);
    InputStream is = null;
    Reader isr = null;
    StringBuilder result = new StringBuilder();
    try {
        is = new FileInputStream(file);
        isr = new InputStreamReader(is);
        int index;

        while (-1 != (index = isr.read())) {
            result.append((char) index);
        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (null != is)
                is.close();
            if (null != isr)
                isr.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return result.toString();
}

BufferedWriter写文件

public static void writeByBuffered(String filename, String context) {
    File file = new File(filename);
    FileOutputStream fos = null;
    OutputStreamWriter osw = null;
    BufferedWriter bw = null;
    try {
        if (!file.exists()) {
            file.createNewFile();
        }
        fos = new FileOutputStream(file);
        osw = new OutputStreamWriter(fos);
        bw = new BufferedWriter(osw);
        bw.write(context);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (null != bw) {
            try {
                bw.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if (null != osw) {
            try {
                osw.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if (null != fos) {
            try {
                fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

OutputStreamWriter写文件

public static void write(String filename, String context) {
    File file = new File(filename);
    FileOutputStream fos = null;
    OutputStreamWriter osw = null;
    try {
        if (!file.exists()) {
            file.createNewFile();
        }
        fos = new FileOutputStream(file);
        osw = new OutputStreamWriter(fos);
        osw.write(context);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (osw != null) {
            try {
                osw.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        if (null != fos) {
            try {
                fos.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}