Java IO beginners

JavaIO programming

I/o system

File

File creation

Single file creation

@test // File creation public void IoFilePractise() throws IOException {File File = new File("D:\\file\\1.txt"); // Check whether the file directory existsif(! file.getParentFile().exists()) { System.out.println("D:\\file directory does not exist, create directory immediately"); file.getParentFile().mkdir(); } // Check whether 1. TXT existsif(! file.exists()) { System.out.println("1.txt file does not exist, create it now"); file.createNewFile(); }}Copy the code

Multilevel file creation

@Test
    public void IoFilePractise3() throws IOException {
        File file=new File("D:\\file\\B\\B1\\B2\\rose.txt"); // Create multiple hierarchical directoriesif(! file.getParentFile().exists()){ file.getParentFile().mkdirs(); } // create the rose.txt fileif(!file.exists()){
            file.createNewFile();
        }
    }
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File deletion

Delete the specified directory and files. It is worth noting that if you only delete the specified directory, there are other files or directories in the directory, it will not be able to delete successfully

@Test
    public void IoFilePractise1() throws IOException {
        File file = new File("D:\\file\\A\\jack.txt"); // Create A directory and jack.txt file file.getparentFile ().mkdir(); file.createNewFile(); // Try to delete the A directory file.getparentFile ().delete(); // Check whether directory A is successfully deletedif (file.getParentFile().exists()) {
            System.out.println("Directory A has not been deleted");
        } else {
            System.out.println("Directory A was deleted successfully"); }}Copy the code

@test // Based on the above public voidIoFilePractise2() {
        File file = new File("D:\\file\\A\\jack.txt"); file.delete(); file.getParentFile().delete(); // Check whether directory A is successfully deletedif (file.getParentFile().exists()) {
            System.out.println("Directory A has not been deleted");
        } else {
            System.out.println("Directory A was deleted successfully"); }}Copy the code

Output file directory

Count D disk below all the file number and output the name, find all TXT files and output and statistics

    private static int fileNumber = 0;
    private static int txtFileNumber = 0;
    private static int directoryNumber = 0;

    @Test
    public void IoFilePractise4() {
        String filePath = "D:\\";
        findFile(filePath);
        System.out.println("Number of files:" + fileNumber);
        System.out.println("Number of TXT files: + txtFileNumber);
        System.out.println("Number of file directories:"+ directoryNumber); } public void findFile(String filePath) { File file = new File(filePath); File[] listFile = file.listfiles (); // Stop recursion if there are no files under the file directoryif(listFile==null)return; // recursive traversalfor(File fileTemp: listFile) {// If it is a Fileif (fileTemp.isFile()) {
                fileNumber++;
                System.out.println(fileTemp.getName() + "For file");
                if (fileTemp.getName().endsWith(".txt")) {
                    txtFileNumber++;
                    System.out.println(fileTemp.getName() + "Also TXT file"); }}else if (fileTemp.isDirectory()) {
                directoryNumber++;
                System.out.println(fileTemp.getName() + "For file directory"); findFile(fileTemp.getPath()); }}}Copy the code

IO Basic Categories

Most of the methods of subclasses are inherited from the parent class, the parent class of the method is clear, the use of subclasses will be easily solved

InputStream class

OutputStream class

Reader class

Writer class

FileInputStream and FileOutputStream

Read byte by byte

@Test public void FileRead() throws IOException { int count=0; FileInputStream fis = new FileInputStream("D:\\file\\1.txt"); int len; // Read byte by byte and return -1 after readingwhile((len = fis.read()) ! = -1) { System.out.print((char)len); count++; } System.out.println("Count of reads :"+count);
        fis.close();
    }

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Read multiple bytes at a time

@Test public void FileRead() throws IOException { int count=0; FileInputStream fis = new FileInputStream("D:\\file\\1.txt"); byte[] n=new byte[1024]; int len; // Read byte by byte and return -1 after readingwhile((len = fis.read(n)) ! // New String(byte[] bytes, int offset, int length) decodes the specified byte subarray using the platform's default character set, Construct a new String system.out.println (new String(n,0,len)); count++; } System.out.println("Count of reads :"+count);
        fis.close();
    }
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File is written to

@test public void FileWrite() throws IOException {// Add FileOutputStream fos=new FileOutputStream("D:\\file\\1.txt".true); // Write a single byte fos.write(98); // Write multiple bytes fos.write(",Hello World!".getBytes());
        fos.close();
    }
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File copy

TXT public void FileCopy() throws IOException {// If 1.txt and 2.txt files are not available, FileOutputStream fos=new must be created in advance FileOutputStream("D:\\file\\2.txt");
        FileInputStream fis=new FileInputStream("D:\\file\\1.txt");
        int len;
        byte[] n=new byte[1024];
        while((len=fis.read(n))! =-1){ fos.write(n,0,len); } fos.close(); fis.close(); }Copy the code

BuffereInputStream and BuffereOutputStream

Buffer stream copy

@test public void FileBuffer() throws IOException {// The object requiring FileInputStream and FileOutStream BufferedInputStream bis = new BufferedInputStream(new FileInputStream("D:\\file\\1.txt"));
        BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("D:\\file\\2.txt"));
        int len;
        while((len = bis.read()) ! = -1){ bos.write(len); } bos.close(); bis.close(); }Copy the code

InputStreamReader and OutputStreamWriter

With copies in Chinese

@test public void FileStream() throws IOException {// Add: InputStreamReader isr=new InputStreamReader(new FileInputStream())"D:\\file\\1.txt"),"GBK");
        OutputStreamWriter osw=new OutputStreamWriter(new FileOutputStream("D:\\file\\2.txt"),"GBK");
        int len;
        char[] n=new char[1014];
        while((len= isr.read(n))! =-1){ System.out.println(new String(n,0,len)); osw.write(n,0,len); } isr.close(); osw.close(); }Copy the code

The ObjectOutputStream and ObjectInputStream

ObjectOutputStream is serializing streams, ObjectInputStream is deserializing streams, Serializable interface must be implemented, otherwise Serializable interface cannot be serialized. If an attribute in an object has the transient and static keywords, it will not be serialized.

Write and read objects

import java.io.Serializable;

public class Book implements Serializable {
    private String id;
    private String name;
    private int money;
    private transient int weight;

    @Override
    public String toString() {
        return "Book{" +
                "id='" + id + '\'' + ", name='" + name + '\'' + ", money=" + money + ", weight=" + weight + '}'; } public Book(String id, String name, int money, int weight) { this.id = id; this.name = name; this.money = money; this.weight = weight; } ----- getter and setter----- } @Test public void ObjectTest() throws IOException, ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("D:\\file\\1.txt", true)); oos.writeInt(99); oos.writeObject(new Book("001","My Chinese dream", 100,)); oos.close(); Ois = new ObjectInputStream(new FileInputStream("D:\\file\\1.txt")); int readInt = ois.readInt(); Book book = (Book) ois.readObject(); System.out.println(readInt); System.out.println(book); ois.close(); }Copy the code

At the end

As a Java beginner, to understand IO to this point is almost the same, the back can be based on interest or actual needs of the project to continue to learn. I myself am also a Java rookie, still in school, Java foundation is very poor, write blog is mainly with the mentality of learning, if there is something wrong in the above hope to point out.