Java IO（六）- Print流

Print流（只有输出流没有输入流）

PrintWriter和PrintStream都属于输出流，分别针对于字符和字节

PrintWriter和PrintStream提供了重载的print方法

Println方法用于多种数据类型的输出

PrintWriter和PrintStream的输出操作不会抛出异常，用户通过检测错误状态获取错误信息

PrintWriter和PrintStream有自动flush方法

构造方法：

PrintWriter(File file)
Creates a new PrintWriter, without automatic line flushing, with the specified file.
PrintWriter(File file, String csn)
Creates a new PrintWriter, without automatic line flushing, with the specified file and charset.
PrintWriter(OutputStream out)
Creates a new PrintWriter, without automatic line flushing, from an existing OutputStream.
PrintWriter(OutputStream out, boolean autoFlush)
Creates a new PrintWriter from an existing OutputStream.
PrintWriter(String fileName)
Creates a new PrintWriter, without automatic line flushing, with the specified file name.
PrintWriter(String fileName, String csn)
Creates a new PrintWriter, without automatic line flushing, with the specified file name and charset.
PrintWriter(Writer out)
Creates a new PrintWriter, without automatic line flushing.
PrintWriter(Writer out, boolean autoFlush)
Creates a new PrintWriter.

PrintStream(File file)
Creates a new print stream, without automatic line flushing, with the specified file.
PrintStream(File file, String csn)
Creates a new print stream, without automatic line flushing, with the specified file and charset.
PrintStream(OutputStream out)
Creates a new print stream.
PrintStream(OutputStream out, boolean autoFlush)
Creates a new print stream.
PrintStream(OutputStream out, boolean autoFlush, String encoding)
Creates a new print stream.
PrintStream(String fileName)
Creates a new print stream, without automatic line flushing, with the specified file name.
PrintStream(String fileName, String csn)
Creates a new print stream, without automatic line flushing, with the specified file name and charset.

例子一

    public static void main(String[] args) {
        try {
            PrintStream ps = null;
            FileOutputStream fos = new FileOutputStream("d:\\bak\\log.dat");
            ps = new PrintStream(fos);
            if(ps != null) {
                System.setOut(ps);//把ps设置成System.out.println();不再输出在控制台了
            }
            int ln = 0;
            for(char c = 0; c <= 60000; c++) {
                System.out.print(c + "");
                if( ln++ >= 100) {
                    System.out.println();
                    ln = 0;
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

结果：d:\\bak\\log.dat，log.data文件

例子二、

    public static void main(String[] args) {
        try {
            PrintStream ps = System.out;
            BufferedReader br = new BufferedReader(new FileReader("d:\\bak\\log.dat"));
            String s = null;
            while((s = br.readLine()) != null) {
                ps.println(s);
            }
            br.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

结果：

例子三、

    public static void main(String[] args) {
        try {
            String s = null;
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            FileWriter fw = new FileWriter("d:\\bak\\logfile.log", true);//日志
            PrintWriter pw = new PrintWriter(fw);
            while ((s = br.readLine()) != null) {
                if("exit".equalsIgnoreCase(s))
                    break;
                System.out.println(s.toUpperCase());
                pw.println("--------");
                pw.println(s.toUpperCase());
                pw.flush();
            }
            pw.println("=====" + new Date() + "======");
            pw.flush();
            pw.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

结果：

控制台：
12121212121
12121212121
adasdasdasdasd
ADASDASDASDASD
exit

文件：d:\\bak\\logfile.log，logfile.log文件