毕向东_Java基础视频教程第19天_IO流（20~22）

Posted 2020-08-29 又是火星人

第19天-20-IO流(改变标准输入输出设备)

static void setIn(InputStream in) 　　Reassigns the "standard" input stream.

static void setOut(PrintStream out)　 Reassigns the "standard" output stream.

package bxd;

import java.io.*;

public class TransStreamDemo3 {
    public static void main(String[] args) throws IOException {

        // 并不常用
        System.setIn(new FileInputStream("s.txt"));
        System.setOut(new PrintStream("out.txt"));

        BufferedReader bufr = new BufferedReader(new InputStreamReader(System.in));
        BufferedWriter bufw = new BufferedWriter(new OutputStreamWriter(System.out));

        String line;
        while ((line = bufr.readLine()) != null) {
            if ("eof".equals(line)) break;
            bufw.write(line);
            bufw.newLine();
            bufw.flush();
        }
        bufr.close();
        bufw.close();
    }
}

第19天-21-IO流(异常的日志信息)

void printStackTrace(PrintStream s)　　Prints this throwable and its backtrace to the specified print stream.

package bxd;

import java.io.PrintStream;
import java.text.SimpleDateFormat;
import java.util.Date;

public class ExceptionInfo {
    public static void main(String[] args) {
        try {
            // 数组越界访问
            int[] array = new int[2];
            System.out.println(array[3]);
        } catch (Exception e) {
            PrintStream printStream = null;
            String time = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
            try {
                printStream = new PrintStream("ExceptionInfo.txt");
                printStream.println(time);
                //printStream.write(time.getBytes());
            } catch (Exception ex) {
                throw new RuntimeException("日志文件创建失败");
            }
            e.printStackTrace(printStream);
        }   // 实际项目中会使用log4j.
    }
} 

第19天-22-IO流(打印系统信息)

static Properties getProperties() 　　Determines the current system properties.

package bxd;

import java.io.IOException;
import java.io.PrintStream;
import java.util.Properties;

public class SystemInfo {
    public static void main(String[] args) throws IOException {
        Properties prop = System.getProperties();
        prop.list(new PrintStream("Sysinfo.txt"));
    }
}