Java-IO之FileReader和FileWriter

FileReader是用于读取字符流的类，它继承于InputStreamReader，要读取原始字节流，考虑使用FileInputStream；FileWriter是用于写入字符流的类，继承于OutputStreamWriter，要写入原始字节流，考虑使用FileOutputStream。

FileReader和FileWriter的示例代码：

public class FileReaderWriterTest {

    private static final String FileName = "file.txt";
    private static final String CharsetName = "utf-8";

    public static void main(String[] args) {
        testWrite();
        testRead();
    }

    /**
     * OutputStreamWriter 演示函数
     *
     */
    private static void testWrite() {
        try {
            // 创建文件“file.txt”对应File对象
            File file = new File(FileName);
            // 创建FileOutputStream对应FileWriter：将字节流转换为字符流，即写入out1的数据会自动由字节转换为字符。
            FileWriter out1 = new FileWriter(file);
            // 写入10个汉字
            out1.write("字节流转为字符流示例");
            // 向“文件中”写入"0123456789"+换行符
            out1.write("0123456789\n");

            out1.close();

        } catch(IOException e) {
            e.printStackTrace();
        }
    }

    /**
     * InputStreamReader 演示程序
    */
    private static void testRead() {
        try {
            // 方法1：新建FileInputStream对象
            // 新建文件“file.txt”对应File对象
            File file = new File(FileName);
            FileReader in1 = new FileReader(file);

            // 测试read()，从中读取一个字符
            char c1 = (char)in1.read();
            System.out.println("c1="+c1);

            // 测试skip(long byteCount)，跳过4个字符
            in1.skip(6);

            // 测试read(char[] cbuf, int off, int len)
            char[] buf = new char[10];
            in1.read(buf, 0, buf.length);
            System.out.println("buf="+(new String(buf)));

            in1.close();
        } catch(IOException e) {
            e.printStackTrace();
        }
    }
}

运行结果：

c1=字

buf=流示例0123456

基于JDK8的FileReader的源代码：

public class FileReader extends InputStreamReader {

    /**
     * Creates a new <tt>FileReader</tt>, given the name of the
     * file to read from.
     *
     * @param fileName the name of the file to read from
     * @exception  FileNotFoundException  if the named file does not exist,
     *                   is a directory rather than a regular file,
     *                   or for some other reason cannot be opened for
     *                   reading.
     */
    public FileReader(String fileName) throws FileNotFoundException {
        super(new FileInputStream(fileName));
    }

    /**
     * Creates a new <tt>FileReader</tt>, given the <tt>File</tt>
     * to read from.
     *
     * @param file the <tt>File</tt> to read from
     * @exception  FileNotFoundException  if the file does not exist,
     *                   is a directory rather than a regular file,
     *                   or for some other reason cannot be opened for
     *                   reading.
     */
    public FileReader(File file) throws FileNotFoundException {
        super(new FileInputStream(file));
    }

    /**
     * Creates a new <tt>FileReader</tt>, given the
     * <tt>FileDescriptor</tt> to read from.
     *
     * @param fd the FileDescriptor to read from
     */
    public FileReader(FileDescriptor fd) {
        super(new FileInputStream(fd));
    }

}

由源码分析得，FileReader继承于InputStreamReader，因此是使用的父类的操作。

基于JDK8 的FileWriter的源码分析：

public class FileWriter extends OutputStreamWriter {

    /**
     * Constructs a FileWriter object given a file name.
     *
     * @param fileName  String The system-dependent filename.
     * @throws IOException  if the named file exists but is a directory rather
     *                  than a regular file, does not exist but cannot be
     *                  created, or cannot be opened for any other reason
     */
    public FileWriter(String fileName) throws IOException {
        super(new FileOutputStream(fileName));
    }

    /**
     * Constructs a FileWriter object given a file name with a boolean
     * indicating whether or not to append the data written.
     *
     * @param fileName  String The system-dependent filename.
     * @param append    boolean if <code>true</code>, then data will be written
     *                  to the end of the file rather than the beginning.
     * @throws IOException  if the named file exists but is a directory rather
     *                  than a regular file, does not exist but cannot be
     *                  created, or cannot be opened for any other reason
     */
    public FileWriter(String fileName, boolean append) throws IOException {
        super(new FileOutputStream(fileName, append));
    }

    /**
     * Constructs a FileWriter object given a File object.
     *
     * @param file  a File object to write to.
     * @throws IOException  if the file exists but is a directory rather than
     *                  a regular file, does not exist but cannot be created,
     *                  or cannot be opened for any other reason
     */
    public FileWriter(File file) throws IOException {
        super(new FileOutputStream(file));
    }

    /**
     * Constructs a FileWriter object given a File object. If the second
     * argument is <code>true</code>, then bytes will be written to the end
     * of the file rather than the beginning.
     *
     * @param file  a File object to write to
     * @param     append    if <code>true</code>, then bytes will be written
     *                      to the end of the file rather than the beginning
     * @throws IOException  if the file exists but is a directory rather than
     *                  a regular file, does not exist but cannot be created,
     *                  or cannot be opened for any other reason
     * @since 1.4
     */
    public FileWriter(File file, boolean append) throws IOException {
        super(new FileOutputStream(file, append));
    }

    /**
     * Constructs a FileWriter object associated with a file descriptor.
     *
     * @param fd  FileDescriptor object to write to.
     */
    public FileWriter(FileDescriptor fd) {
        super(new FileOutputStream(fd));
    }

}