Java文件

jdk7以后,通过try-with-resources技术,可以在try中实例化资源,让它在结束后自动关闭.

package stream;
  
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
  
public class TestStream {
  
    public static void main(String[] args) {
        File f = new File("d:/lol.txt");
  
        //把流定义在try()里,try,catch或者finally结束的时候，会自动关闭
        try (FileInputStream fis = new FileInputStream(f)) {
            byte[] all = new byte[(int) f.length()];
            fis.read(all);
            for (byte b : all) {
                System.out.println(b);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
  
    }
}

jdk9中,可以直接在try中使用常量资源,而不需要重新定义了.

// New and improved try-with-resources statement in JDK 9
try (resource1;
     resource2) {
    // Use of resource1 and resource 2.
}

流流

InputStream输入流/OutputStream输出流.字节输入输出

FileInputStream fis = new FileInputStream(new File("C:/"));

Reader字符输入流Writer字符输出流(默认按操作系统编码GBK)

FileReader fr = new FileReader(f);

自定义编码字符流InputStreamReader

InputStreamReader isr = new InputStreamReader(new FileInputStream(f),Charset.forName("UTF-8"))

字符缓存流BufferedReader PrintWriter flush

        try (
                FileReader fr = new FileReader(f);
                BufferedReader br = new BufferedReader(fr);
            )
        {
            while (true) {
                // 一次读一行
                String line = br.readLine();
                if (null == line)
                    break;
                System.out.println(line);
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }



        try (
                // 创建文件字符流
                FileWriter fw = new FileWriter(f);
                // 缓存流必须建立在一个存在的流的基础上              
                PrintWriter pw = new PrintWriter(fw);              
        ) {
            pw.println("garen kill teemo");
            pw.println("teemo revive after 1 minutes");
            pw.println("teemo try to garen, but killed again");
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }



        //向文件lol2.txt中写入三行语句
        File f =new File("d:/lol2.txt");
        //创建文件字符流
        //缓存流必须建立在一个存在的流的基础上
        try(FileWriter fr = new FileWriter(f);PrintWriter pw = new PrintWriter(fr);) {
            pw.println("garen kill teemo");
            //强制把缓存中的数据写入硬盘，无论缓存是否已满
                pw.flush();           
            pw.println("teemo revive after 1 minutes");
                pw.flush();
            pw.println("teemo try to garen, but killed again");
                pw.flush();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

数据流DataInputStream数据输入流 DataOutputStream数据输出流

数据输入流只能识别数据输出流写入的数据.
优点在于可以直接读取不同类型的数据.

package stream;
      
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
      
public class TestStream {
      
    public static void main(String[] args) {
        write();
        read();
    }
 
    private static void read() {
        File f =new File("d:/lol.txt");
        try (
                FileInputStream fis  = new FileInputStream(f);
                DataInputStream dis =new DataInputStream(fis);
        ){
            boolean b= dis.readBoolean();
            int i = dis.readInt();
            String str = dis.readUTF();
             
            System.out.println("读取到布尔值:"+b);
            System.out.println("读取到整数:"+i);
            System.out.println("读取到字符串:"+str);
 
        } catch (IOException e) {
            e.printStackTrace();
        }
         
    }
 
    private static void write() {
        File f =new File("d:/lol.txt");
        try (
                FileOutputStream fos  = new FileOutputStream(f);
                DataOutputStream dos =new DataOutputStream(fos);
        ){
            dos.writeBoolean(true);
            dos.writeInt(300);
            dos.writeUTF("123 this is gareen");
        } catch (IOException e) {
            e.printStackTrace();
        }
         
    }
}

对象流ObjectInputStream/ObjectOutputStream

实现了Serializable接口的类的对象可以进行序列化.

package stream;
    
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
  
import charactor.Hero;
    
public class TestStream {
    
    public static void main(String[] args) {
        //创建一个Hero garen
        //要把Hero对象直接保存在文件上，务必让Hero类实现Serializable接口
        Hero h = new Hero();
        h.name = "garen";
        h.hp = 616;
          
        //准备一个文件用于保存该对象
        File f =new File("d:/garen.lol");
 
        try(
            //创建对象输出流
            FileOutputStream fos = new FileOutputStream(f);
            ObjectOutputStream oos =new ObjectOutputStream(fos);
            //创建对象输入流              
            FileInputStream fis = new FileInputStream(f);
            ObjectInputStream ois =new ObjectInputStream(fis);
        ) {
            oos.writeObject(h);
            Hero h2 = (Hero) ois.readObject();
            System.out.println(h2.name);
            System.out.println(h2.hp);
               
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
            
    }
}

控制台输入流System.in

用Scanner更加方便的使用控制台输入吧.
Scanner s = new Scanner(System.in);

参考资料
HOW2J教程
Way Lau