Print stream:

There are two classes: PrintStream and PrintWriter. The methods of the two classes are the same. The difference lies in the constructor

PrintStream: construction method: receive File type, receive string File name, receive byte output stream

PringWriter: construction method: receive File type, receive string File name, receive byte output stream, receive character output stream

Adding functionality to other streams makes it easy to print various data values, except that it never throws IO exceptions

method:

package demo;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;

public class PrintWriterDemo {
    public static void main(String[] args) throws IOException {
        function1();
        function2();
        function3();
    }

    public static void function1() throws FileNotFoundException {
        File file = new File("d:\\1.txt");
        PrintWriter pw = new PrintWriter(file);
        pw.println(100);// Not written d，It's 100, print as is
        pw.write(100);// What is written is d
        pw.flush();
        pw.close();
    }

    public static void function2() throws FileNotFoundException {
        FileOutputStream fos1 = new FileOutputStream("d:\\2.txt");
        PrintWriter pw1 = new PrintWriter(fos1);
        pw1.println("Print stream");
        pw1.flush();
        pw1.close();
    }

    public static void function3() throws IOException {
        FileWriter fw1 = new FileWriter("d:\\4.txt");
        PrintWriter pw1 = new PrintWriter(fw1);
        pw1.println("Print stream");
        pw1.flush();
        pw1.close();
    }
}

Print stream auto refresh:

package demo;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintWriter;

public class PrintWriterDemo {
    public static void main(String[] args) throws IOException {
        function1();
    }

    public static void function1() throws FileNotFoundException {
        FileOutputStream fos1 = new FileOutputStream("d:\\1.txt");
        PrintWriter pw1 = new PrintWriter(fos1, true);
        // The second parameter is auto Book refresh. If it is, no need to write flush Method
        pw1.println("I");
        pw1.println("Love");
        pw1.println("You");
        pw1.close();
    }
}

Print stream copy text file:

package demo;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;

public class Copy {
    public static void main(String[] args) throws IOException {
        BufferedReader bfr1 = new BufferedReader(new FileReader("d:\\1.txt"));
        PrintWriter pw1 = new PrintWriter(new FileWriter("d:\\2.txt"), true);
        String line = null;
        while ((line = bfr1.readLine()) != null) {
            pw1.println(line);
        }
        pw1.close();
        bfr1.close();
    }
}

Finally, simply write down the tool class, which can greatly reduce the code amount:

apache's commons tool class:

Download it on the official website, copy it to the new lib folder under the current project, and right-click build path

Several powerful common methods:

package demo;

import java.io.File;
import java.io.IOException;

import org.apache.commons.io.FileUtils;
import org.apache.commons.io.FilenameUtils;

public class CommonsDemo {
    public static void main(String[] args) throws IOException {
        function1();//Filename operation
        function2();//File operation
    }
    public static void function1(){
        String name = FilenameUtils.getExtension("a.java");
        System.out.println(name);//Output: java
        
        String filename = FilenameUtils.getName("d:\\b.java");
        System.out.println(filename);//Output: b.java
        
        boolean a = FilenameUtils.isExtension("c.java", "java");
        System.out.println(a);//output true，The method of judging the file suffix
    }    
    
    public static void function2() throws IOException{
        //Read the contents of a text file
        String s1 = FileUtils.readFileToString(new File("d:\\1.txt"));
        System.out.println(s1);
        
        //Write text file
        FileUtils.writeStringToFile(new File("d:\\b.txt"), "java");
        //Here you create a text file and write a string java
        
        //Copy file (not limited to text)
        FileUtils.copyFile(new File("d:\\1.txt"), new File("d:\\11.txt"));
        
        //Copy folder
        FileUtils.copyDirectoryToDirectory(new File("f:\\new"), new File("d:\\new"));
    }
}