I/O：读和写 及文件

File类 输入 输出流

File类

构造方法：

File(String pathname) 
File(String parent, String child)
File(File parent, String child)

作用

查看文件属性：canRead(), isFile(), lastModified()
创建或删除目录：mkdir(),delete()
列出目录下的所有文件：list()
判断文件是否存在：exists()
重新命名文件：renameTo()

输入 输出流

InputStream
FileInputStream
OutputStream
​ FileOutputStream
Reader
FileReader
Writer
​ FileWriter

InputStream类

OutputStream类

Reader与Writer类

/**
 * 本例子演示了如何用面向byte的方式 读取、写入文件
 * @author Administrator
 *
 */
public class ReadWriteFileByteDemo {
    public static int CHUNK_SIZE = 4096;

    public ReadWriteFileByteDemo() {
        // TODO Auto-generated constructor stub
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        try {
            copyFile("D:\\elipse\\course\\src.jpg", "D:\\elipse\\course\\dest.jpg");
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    /**
     * 复制IO流
     * @param in
     * @param out
     * @throws IOException
     */
    public static void copyIO(InputStream in, OutputStream out) throws IOException {
        byte[] buf = new byte[CHUNK_SIZE];
        /**
         * 从输入流读取内容的典型方法
         */
        int len = in.read(buf);
        while (len != -1) {
            out.write(buf, 0, len);
            len = in.read(buf);
        }
    }

    /**
     * 复制文件
     * @param fsrc
     * @param fdest
     * @throws IOException
     */
    public static void copyFile(String fsrc, String fdest) throws IOException {
        InputStream in=null;
        OutputStream out=null;
        try {
            in = new FileInputStream(fsrc);
            out = new FileOutputStream(fdest, true);
            copyIO(in, out);    
        } finally {
            close(in);
            close(out);
        }
    }
    
    /**
     * 关闭一个输入 输出流
     * @param inout
     */
    public static void close(Closeable inout) {
        if (inout != null) {
            try {
                inout.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }

}

/**
 * 本例子演示了如何使用char的方式 读取、写入文件
 * @author Administrator
 *
 */
public class ReadWriteFileCharDemo {
    public static int CHUNK_SIZE = 4096;

    public ReadWriteFileCharDemo() {
        // TODO Auto-generated constructor stub
    }

    public static void main(String[] args) {
        
        try {
            String s = readFile("D:/elipse/course/demo.txt");
            System.out.println(s);
    //          List<String> list=readLine("D:/elipse/course/red.txt");
    //          for(int i=0;i<list.size();i++) {
    //              System.out.println(list.get(i));
    //          }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    /**
     * 从一个文件中读取字符串
     * @param fsrc
     * @return
     * @throws IOException
     */
    public static String readFile(String fsrc) throws IOException {
        Reader reader = null;
        try {
            StringBuffer buf = new StringBuffer();          
            char[] chars = new char[CHUNK_SIZE];
            reader = new FileReader(fsrc);          
            int readed = reader.read(chars);
            while (readed != -1) {
                buf.append(chars, 0, readed);               
                readed = reader.read(chars);
            }
            return buf.toString();
        } finally {
            close(reader);
        }
    }

    /**
     * 从一个文本文件中，一次读取一行，放到list中
     * @param fsrc
     * @return
     * @throws IOException
     */
    public static List<String> readLine(String fsrc) throws IOException {
        Reader reader = null;
        LineNumberReader lineReader = null;
        try {
            reader = new FileReader(fsrc);
            lineReader = new LineNumberReader(reader);
            String line = lineReader.readLine();
            List<String> lines = new ArrayList<String>();
            while (line != null) {
                lines.add(line);
                line = lineReader.readLine();
            }
            return lines;
        } finally {
            close(lineReader);
            close(reader);
        }
    }

    /**
     * 把字符串写到文件中
     * @param fileName
     * @param content
     * @throws IOException
     */
    public void writeFile(String fileName, String content) throws IOException {
        OutputStream out = null;
        try {
            
            out = new FileOutputStream(fileName, false);
            out.write(content.getBytes());
            out.flush();
        } finally {
            close(out);
        }

    }

    /**
     * 关闭输入输入流
     * @param inout
     */
    public static void close(Closeable inout) {
        if (inout != null) {
            try {
                inout.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

流有两种基本形式：输入流和输出流，根据程序是作为数据流的目的端还是源端来划分。程序首先要打开一个流，才能与数据文件进行通信。

通过输入流，程序可以从数据文件读取数据，但不可向输入流中写入数据；反之，通过输出流，程序可以向数据文件中写入数据。程序与其他设备间的I/O也可以使用流，这时可将设备看作是一个数据文件。