【java】io流之缓冲、数据、输出、转换流基本使用

缓冲流：

public class BufferedReaderTest01 {
    public static void main(String[] args) throws Exception{
        FileReader reader = new FileReader("wenjian");
        
        BufferedReader br = new BufferedReader(reader);

        //readline()方法返回一个字符串类型
        //如 String s = br.readline();
        //readline()方法读取一个文本行(一行)，但不带换行符
        String str = null;
        while((str = br.readLine()) != null){
            System.out.println(str);
        }

        br.close();

    }
}

public class BufferedReaderTest02 {
    public static void main(String[] args) throws Exception{
        //字节流
        FileInputStream fis = new FileInputStream("wenjian");

        //通过转换流转换（InputStreamReader将字节流转换为字符流）
        //这里fis为节点流，reader为包装流
        InputStreamReader reader = new InputStreamReader(fis);

        //这个构造方法只能传一个字符流，不能传字节流，若需传入字节流，需要先将字节流转换为字符流
        //这里reader为节点流，br为包装流
        BufferedReader br = new BufferedReader(reader);

        //以上代码合并
        BufferedReader br1 = new BufferedReader(new InputStreamReader(new FileInputStream("wenjian")));
    }
}

public class BufferedWriterTest01 {
    public static void main(String[] args) throws Exception {
        BufferedWriter bw = new BufferedWriter(new FileWriter("abc",true));
        bw.write("hahahaha");
        bw.write("nihaoa");

        //刷新
        bw.flush();
        //关闭
        bw.close();
    }
}

数据流：

public class DataInputStreamTest01 {
    public static void main(String[] args) throws Exception{
        DataInputStream dis = new DataInputStream(new FileInputStream("data"));
        //读数据
        short s = dis.readShort();
        int i = dis.readInt();
        String str = dis.readUTF();
        float f = dis.readFloat();

        System.out.println(s);
        System.out.println(i);
        System.out.println(f);
        System.out.println(str);

        dis.close();
    }
}

public class DataOutputStreamTest01 {
    public static void main(String[] args) throws Exception {
        DataOutputStream dos = new DataOutputStream(new FileOutputStream("data"));
        //写入数据
        short s = 12;
        int i = 100;
        String str = "haha";
        float f = 3.0f;
        //写
        dos.writeShort(s);
        dos.writeInt(i);
        dos.writeUTF(str);
        dos.writeFloat(f);

        dos.flush();
        dos.close();

    }
}

输出流：

**
 * 标准字节输出流（默认输出到后台）：PrintStream
 * 标准输出流不需要手动close()关闭
 */
public class PrintStreamTest01 {
    public static void main(String[] args) throws Exception{
        //联合起来写
        //这里默认输出到控制台
        System.out.println("hello word!");

        //分开写
        PrintStream ps = System.out;
        ps.println("hello world");
        ps.println("heihei");
        ps.println("xixi");

        //修改输出方向，输出到log文件当中
        PrintStream ps1 = new PrintStream(new FileOutputStream("log",true));
        System.setOut(ps1);
        //以下不再输出到控制台，即输出搭配log文件中
        System.out.println("asdf");
        System.out.println("123");
        System.out.println("hello world!");

    }
}

public class LogG {
    public static void log(String msg){
        //指向一个日志文件，修改输出方向
        try {
            System.setOut(new PrintStream(new FileOutputStream("log.txt",true)));
            //当前日期时间
            Date nowTime = new Date();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            String strTime = sdf.format(nowTime);

            System.out.println(strTime + ":" + msg);
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }

    }

    public static void main(String[] args) {
        log("调用了xxxx类的某某方法");
        log("调用了PrintStram生成日志");
        log("这是一个日志工具");
        log("用户尝试登录，尝试失败，密码错误或用户名不正确");
    }
}