IO-------常见字符流

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字符流的由来：字符流读取文字字节数据以后，不直接操作而是先查指定的编码表，获取对应的文字，再对该文字进行操作，简单说字符流就是字节流+编码表。所以对于文字的操作优先使用字符流。

一、利用字符流实现文本文档的拷贝：较标准的异常处理格式

public class CopyFileTest {

    private static final int BUFFER_SIZE = 1024;

    public static void main(String[] args) {
        FileReader fr = null;
        FileWriter fw = null;
        try {
            fr = new FileReader("demo.txt");
            fw = new FileWriter("demo_copy.txt");

            // 创建一个临时容器，用于缓存读取到的字符
            char[] buf = new char[BUFFER_SIZE];

            // 定义一个变量记录读取到的字符数
            int len;
            while ((len = fr.read(buf)) != -1) {
                fw.write(buf, 0, len);
            }
        } catch (Exception e) {
            throw new RuntimeException("读写失败");
        } finally {
            if (fw != null) {
                try {
                    fw.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fr != null) {
                try {
                    fr.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

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二、字符流与字节流读取文本文件的耗时比较：

Class TimeCompare{

    public static void main(String[] args) throws IOException {

    long l1 = System.currentTimeMillis();
    characterCopy();
    long l2 = System.currentTimeMillis();
    System.out.println("字符流耗时：" + (l2 - l1));

    l1 = System.currentTimeMillis();
    byteCopy();
    long l2 = System.currentTimeMillis();
    System.out.println("字节流耗时：" + (l2 - l1));
    }

    /**
     * 字符流操作
     * @throws IOException
     */
    public static void characterCopy() throws IOException {

        FileReader fr = new FileReader("demo.txt");
        FileWriter fw = new FileWriter("copydemo_1.txt");
        int ch;
        while ((ch = fr.read()) != -1) {
            fw.write(ch);
        }
        fw.close();
        fr.close();
    }

    /**
     * 字节流操作
     * @throws IOException
     */
    public static void byteCopy() throws IOException {

        FileInputStream fis = new FileInputStream("demo.txt");
        FileOutputStream fos = new FileOutputStream("democopy_2.txt");
        int ch;
        while ((ch = fis.read()) != -1) {
            fos.write(ch);
        }

        fos.close();
        fis.close();
    }
}

结果：

    字符流耗时：17
    字节流耗时：46

可以看出字符流在操作文本文件的时候效率是较高的。

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三、利用缓冲区提高效率

    public static void bufferCopy() throws IOException {

        long l1 = System.currentTimeMillis();
        FileReader fr = new FileReader("demo.txt");
        BufferedReader bufr = new BufferedReader(fr);

        FileWriter fw = new FileWriter("democopy_3.txt");
        BufferedWriter bufw = new BufferedWriter(fw);

        String line;
        while ((line = bufr.readLine()) != null) {
            bufw.write(line);
            bufw.newLine();
            bufw.flush();
        }

        bufr.close();
        bufw.close();
        long l2 = System.currentTimeMillis();
        System.out.println("字符流缓冲区耗时：" + (l2 -l1));
    }

结果：

     字符流缓冲区耗时：9

可以看到利用缓冲区后效率又有所提高。