第九章 IO操作

梁云亮

2024-03-22 帮助1人

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

学新通

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<User> us = new ArrayList<User>();
		 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

学新通

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();
	}
}

这篇好文章是转载于：学新通技术网

第九章 IO操作

9.1 目录操作

9.2 文件操作

9.3 字节流

9.4 字符流

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