第九章 IO操作

9.1 目录操作

public class Dir1 {

	public static void main(String[] args) {
		//判断目录是否存在
		File f = new File("user");
		if(f.exists()) {
			System.out.println("user目录存在");
		}else {
			f.mkdir();//建立一级目录
			System.out.println("user目录建立成功");
			System.out.println(f.exists());
		}
		
		//建立目录 .mkdir()
		File f2 = new File("c:\\javaok\\book\\my\\user");
		if(!f2.exists()) f2.mkdirs(); //建立多级目录
		
		//建立多级目录  .mkdirs()
		File f3 = new File("c:/code/user");
		if(f3.mkdirs()) {
			System.out.println("建立成功");
		}else{
			System.out.println("已经存在不用建立");
		}
		
		
		//删除目录 只能删除一级空目录
		File f5 = new File("c:/code/abc");
		if(f5.exists() && f5.isDirectory()) {
			f5.delete(); //删除文件或删除一级空目录
		}
		
		File f6 = new File("c:/code");
		f6.delete();
	}

}

9.2 文件操作

• java.io.File

  public class File1 {
  
  	public static void main(String[] args) throws IOException {
  		File f = new File("user");
  		System.out.println(f.isAbsolute());
  		System.out.println(f.isDirectory());
  		System.out.println(f.isHidden());
  		System.out.println(f.isFile());
  		System.out.println(f.exists());
  		
  		//建立文件
  		File uf1 = new File("user1.txt");
  		File uf2 = new File(".","user2.txt");
  		System.out.println(uf1.createNewFile());
  		System.out.println(uf2.createNewFile());
  		
  		//删除文件
  		if(uf1.exists()) uf1.delete();
  		if(uf2.exists()) uf2.deleteOnExit();
  
  	}
  
  }
  
  
  public class File2 {
  	public static void main(String[] args)  {
  		//File f = new File("c:/javaok/a.rar");
  		//f.deleteOnExit();
  		
  		File dir = new File("c:/javaok");
  		if(dir.exists()) {
  			File[] fs = dir.listFiles(); //列出当前目录下的所有文件对象
  			//System.out.println(fs.length);
  			for(File t : fs) {
  				if(t.isFile() && t.getName().endsWith(".rar")) {
  					t.delete();
  				}
  			}
  		}
  	}
  }
  
  
  统计文件代码行，空行数
  
  ```java
  public class File5 {
  	static int num = 0;
  
  	public static void main(String[] args) throws FileNotFoundException {
  		String path = "D:\\eclipse-workspace\\part02\\src\\cn\\Bin2.java";
  		BufferedReader br = new BufferedReader(new FileReader(path));
  		System.out.println(br.lines().filter(e->e.trim().length()>0).count());
  	}
  
  }
  
  

  递归统计文件个数及文件行数实现

  public class File4 {
  	static int num = 0;
      static int rows = 0;
      static int space = 0;
  	public static void main(String[] args) throws Exception {
  		String path = "c:/javaok";
  		
  		//del(new File(path));
  		
  		count(new File("d:/eclipse-workspace"));
  		
  		
  		System.out.printf("%s 共有%d个java程序文件%n","d:/eclipse-workspace",num); //java文件个数
  		System.out.printf("共 %d 行代码%n",rows);
  		System.out.printf("共 %d 空行代码%n",space);
  
  	}
  	
  	public static void count(File dir) throws FileNotFoundException  {
  		if (dir.isDirectory()) {
  			File[] f = dir.listFiles();
  			for (File t : f) {
  				if (t.isDirectory())
  					count(t);
  				if (t.isFile() && t.getName().endsWith(".java")) { 
  					++num;
  					BufferedReader br = new BufferedReader(new FileReader(t));
  					//rows+=br.lines().filter(e->e.trim().length()>0).count();
  					rows+=br.lines().count();
  					
  					BufferedReader br2 = new BufferedReader(new FileReader(t));
  					space+=br2.lines().filter(e->e.trim().length()==0).count();
  				}
  					
  			}
  		} 
  		if (dir.isFile() && dir.getName().endsWith(".rar")) {
  			++num;
  			BufferedReader br = new BufferedReader(new FileReader(dir));
  			//rows+=br.lines().filter(e->e.trim().length()>0).count();
  			rows+=br.lines().count();
  			
  			BufferedReader br2 = new BufferedReader(new FileReader(dir));
  			space+=br2.lines().filter(e->e.trim().length()==0).count();
  		}
  	}
  
  	public static void del(File dir) {
  		if (dir.isDirectory()) {
  			File[] f = dir.listFiles();
  			for (File t : f) {
  				if (t.isDirectory())
  					del(t);
  				if (t.isFile() && t.getName().endsWith(".rar"))
  					t.delete();
  			}
  		} 
  		if (dir.isFile() && dir.getName().endsWith(".rar"))
  			dir.delete();
  	}
  
  }
  
  

9.3 字节流

• java.io.InputStream 输入流，主要是用来读取文件内容的。

• java.io.OutputStream 输出流，主要是用来将内容写入文件的。

• FileInputStream、 FileOutputStream

  public class FileStreamTest {
  	
  	public static void main(String[] args) {
  		//读取文件
  		String f = "D:\\java\\log\\20201222-type.txt";
  		try {
  			FileInputStream fis = new FileInputStream(f);
  			//System.out.println(new String(fis.readAllBytes(),"utf-8"));
  			
  			byte[] buf = new byte[1024];
  			int len = 0;
  			while((len = fis.read(buf))>0) {
  				System.out.println(new String(buf,"utf-8"));
  			}
  		
  			
  			fis.close();
  		}catch(Exception e) {
  			
  		}
  		
  	}
  	
  	
  	public static void write(String str) {
  		try {
  			//建立文件输出流，用来写入内容，true,追加模式
  			FileOutputStream fos = new FileOutputStream("c:/u.txt",true);
  			fos.write(String.format("hello world 中文效果(%1$tF %1$tT)\r\n", System.currentTimeMillis()).getBytes());
  			fos.close();
  		} catch (FileNotFoundException e) {
  			e.printStackTrace();
  		} catch (IOException e) {
  			e.printStackTrace();
  		}
  	}
  }
  
  

• 实现文件复制功能

  
  public class FileCopy {
  
  	public static void main(String[] args) throws IOException {
  		//实现文件复制
  		FileInputStream fis = new FileInputStream("c:/u.jpg");
  		//DataInputStream dis = new DataInputStream(fis);
  		FileOutputStream fos = new FileOutputStream("d:/u2.jpg");
  		//fos.write(fis.readAllBytes());
  		byte[] buf = new byte[1024];
  		int len = 0;
  		while((len = fis.read(buf))!=-1) {
  			fos.write(buf, 0, len);
  		}
  		fo
              s.close();
  		
  
  	}
  
  }
  
  

• RandomAccessFile

  public class StreamTest {
  
  	public static void main(String[] args) throws IOException {
  		RandomAccessFile randf = new RandomAccessFile("c:/u.jpg", "r");
  		
  		//System.out.println(randf.length());
  		//System.out.println(randf.readByte());//-1
  		//System.out.println(randf.readByte());//-40
  		//System.out.println(randf.readByte());//-1
  		//randf.skipBytes(0);//0 -32 1 0   2 16
  		//System.out.println(randf.readByte());//16
  		
  		randf.skipBytes((int)randf.length()-1);
  		System.out.println(randf.readByte());
  
  	}
  
  }
  
  

• ObjectInputStream\ObjectOutputStream

  public class User implements Serializable {
  	private int id;
  	private String name;
  	private int age;
  
  	public int getId() {
  		return id;
  	}
  
  	public void setId(int id) {
  		this.id = id;
  	}
  
  	public String getName() {
  		return name;
  	}
  
  	public void setName(String name) {
  		this.name = name;
  	}
  
  	public int getAge() {
  		return age;
  	}
  
  	public void setAge(int age) {
  		this.age = age;
  	}
  
  	public User(int id, String name, int age) {
  		super();
  		this.id = id;
  		this.name = name;
  		this.age = age;
  	}
  
  	public User() {
  		super();
  		// TODO Auto-generated constructor stub
  	}
  
  	@Override
  	public String toString() {
  		return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
  	}
  
  }
  
  public class ObjectStreamTest {
  
  	public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {
  		// 将java为的实例保存
  		//User u = new User(1, "杰克", 18);
  		 ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("user.dat", true));
  		 
  		 oos.writeObject("aa");
  		 
  
  
  		 List us = new ArrayList();
  		 oos.writeObject(us);
  
  		 
  		// oos.writeObject(u);
  		// oos.close();
  		
  		
  
  		// 读取Object
  		ObjectInputStream ois = new ObjectInputStream(new FileInputStream("user.dat"));
  		User user = (User)ois.readObject();
  		System.out.println(user);
  
  	}
  
  }
  
  
  

  面试题：java中什么是序列化，反序列化？为什么要序列化？

9.4 字符流

• Reader FileReader BufferedReader

• Writer FileWriter BufferedWriter

  
  public class ReaderWriterTest {
  
  	public static void main(String[] args) throws IOException {
  		//写入文件
  		FileWriter fw = new FileWriter("user.dat", true);
  		//fw.write("hello world中文\n\r");
  		//fw.write("hello world中文\n\r");
  		//fw.write("hello world中文\n\r");
  		//fw.close();
  		
  		//读取
  		BufferedReader br = new BufferedReader(new FileReader("user.dat"));
  		//System.out.println(br.lines().count());
  		int rownum = 0;
  		
  		while(br.ready()) {
  			++rownum;
  			System.out.println(br.readLine());
  		}
  		System.out.println(rownum);
  		br.close();
  	}
  }