JAVA study notes—IO flow

Mobile 2023-10-06 09:39:44 views: null

I/O stile

flow concept

  • A channel for transferring data between memory and storage devices

Water (equivalent to data) -> pipes that transmit water (equivalent to flow) -> washbasin (equivalent to memory)

Domestic water -> inflow

Domestic wastewater -> outflow

Classification of flows

By direction【Key points】

  • Input stream: Read the contents of <storage device> into <memory>
  • Output stream: Write the contents in <memory> to <storage device>

by unit

  • Byte stream: in bytes, all data can be read and written
  • Character stream: in character units, only text data can be read and written

by function

  • Node stream: has the read and write functions to actually transfer data
  • Filter flow: Enhanced functionality based on node flow

byte stream

Parent class of byte stream (abstract class)

//InputStream 字节输入流
public int read(){
    
    }
public int read(byte[] b){
    
    }
public int read(byte[] b, int off, int len){
    
    }

// OutputStream 字节输出流
public void write(int n){
    
    }
public void write(byte[] b){
    
    }
public void write(byte[] b, int off, int len){
    
    }

file byte stream

file input stream

//文件字节输入流
public static void main(String[] args) throws Exception{
    
    
    //1. 创建FileInputStream,并指定文件路径
    FileInputStream file = new FileInputStream("路径/a.txt");
    //2. 读取文件
    //2.1 单字节读取
    int data = 0;
    while((data=file.read())!=-1){
    
    
        System.out.print((char) data);
    }
    //2.2.1 一次读取多个字节
    byte[] buf = new byte[3];
    int count = file.read(buf);
    System.out.println(new String(buf));
    System.out.println(count);
    int count2 = file.read(buf);
    System.out.println(new String(buf));
    System.out.println(count2);
   
    //2.2.1 一次读取多个字节
    byte[] buf = new byte[1024];
    int count = 0;
    while ((count=file.read(buf))!=-1){
    
    
        System.out.println(new String(buf,0,count));
    }
    //3. 关闭
    file.close();
    System.out.println("\n执行完毕");
}

file output stream

//FileOutputStream
public static void main(String[] args) throws Exception{
    
    
    //1. 创建FileOutputStream,并指定文件路径
    FileOutputStream fos = new FileOutputStream("路径/b.txt",true);
  	//true 不覆盖
    //2. 输出文件
    fos.write(97);
    fos.write('b');
    fos.write('c');
    String str = "helloworld";
    fos.write(str.getBytes());
    //3. 关闭
    fos.close();
    System.out.println("执行完毕");
}

Picture copy case

public static void main(String[] args) throws Exception {
    
    
    //使用文件字节流实现文件的复制
    // 1 创建流
    // 1.1 文件字节输入流
    FileInputStream fis = new FileInputStream("路径/a.jpg");
    // 1.2 文件字节输出流
    FileOutputStream fos = new FileOutputStream("路径/b.jpg");
    // 2 边读边写
    byte[] buf = new byte[1024];
    int count = 0;
    while((count=fis.read(buf))!=-1){
    
    
        fos.write(buf,0,count);
    }
    // 3 关闭
    fis.close();
    fos.close();
}

byte buffer stream

Buffered stream: BufferedInputStream/ BufferedOutputStream

  • Improve IO efficiency and reduce the number of disk accesses
  • The data is stored in the buffer. Flush writes the contents of the buffer to the file. You can also close directly.
    //BufferedInputStream
    public static void main(String[] args) throws Exception{
    
    
        //1. 创建BufferedInputStream
        FileInputStream fis = new FileInputStream("路径/a.txt");
        BufferedInputStream bis = new BufferedInputStream(fis);
        //2. 读取
        int data = 0;
        while((data=bis.read())!=-1){
    
    
            System.out.print((char)data);
        }
        //自己创建缓冲区
        byte[] buf = new byte[1024];
        int count = 0;
        while((count=bis.read(buf))!=-1){
    
    
            System.out.println(new String(buf,0,count));
        }
        //3. 关闭
        bis.close();
        System.out.println("\n执行完毕");
    }

public static void main(String[] args) throws Exception{
    
    
    //1. 创建BufferedOutputStream 字节输出缓冲流
    FileOutputStream fos = new FileOutputStream("路径/b2.txt");
    BufferedOutputStream bos = new BufferedOutputStream(fos);
    //2. 写入文件
    for(int i=0;i<10;i++){
    
    
        bos.write("helloworld\n".getBytes());//写入缓冲区，没超过8K缓冲区
        bos.flush();//刷新到硬盘
    }
    //3. 关闭
    bos.close();
    System.out.println("\n执行完毕");
}

object stream

  • Enhanced buffer functionality
  • Enhanced functions of reading and writing 8 basic data types and strings
  • Enhanced functionality for reading and writing objects
    • readObject()Read an object from the stream
    • writeObject(Object obj)Write an object to the stream

The process of using streaming objects is called serialization and deserialization

Serialization and deserialization

Serialization

  • The serialization class must implement the Serializable interface
//实现接口 标记接口
public class Student implements Serializable {
    
    }

//使用ObjectOutputStream 实现对象的序列化
public static void main(String[] args) throws Exception{
    
    
        //1. 创建对象流
        FileOutputStream fos = new FileOutputStream("路径/stu.bin");
        ObjectOutputStream oos = new ObjectOutputStream(fos);
        //2. 序列化（写入操作）
        Student s1 = new Student("zhangsan",20);
        oos.writeObject(s1);
        //3. 关闭
        oos.close();
        System.out.println("执行完毕");
}

Deserialization

// 使用ObjectInputSteam实现反序列化（读取重构对象）
public static void main(String[] args) throws Exception{
    
    
        //1. 创建对象流
        FileInputStream fis = new FileInputStream("路径/stu.bin");
        ObjectInputStream ois = new ObjectInputStream(fis);
        //2. 读取文件（反序列化）
        Student s = (Student) ois.readObject();
        //关闭
        ois.close();
        System.out.println("执行完毕");
        System.out.println(s.toString());//Student{name='zhangsan', age=20}
}

Precautions

  1. To be serialized, a class must implement the Serializable interface.
  2. Object properties in serialization classes require the implementation of the Serializable interface
  3. Serialization version number ID, ensuring that the serialized class and the deserialized class are the same class
  4. Use transient (transient) modification attribute, this attribute cannot be serialized
  5. Static properties cannot be serialized
  6. Serializing multiple objects can be achieved with the help of collections

The specific serialization process is as follows:

​ During the serialization operation, the system will write the serialVersionUID of the current class into the serialization file. When deserializing, the system will detect the serialVersionUID in the file to determine whether it is consistent with the serialVersionUID of the current class. If it is consistent, the sequence will be specified. The version of the deserialized class is the same as the current class version, and the deserialization can be successful, otherwise it will fail.

//序列化多个对象，可以借助集合来实现
//2. 序列化（写入操作）
Student s1 = new Student("zhangsan",20);
Student s2 = new Student("lisi",25);
ArrayList<Student> list = new ArrayList<>();
list.add(s1);
list.add(s2);
oos.writeObject(list);

//2. 读取文件（反序列化）
//Student s = (Student) ois.readObject();
ArrayList<Student> list = (ArrayList<Student>) ois.readObject();
//关闭
ois.close();
System.out.println("执行完毕");
System.out.println(list.toString());
//[Student{name='zhangsan', age=0}, Student{name='lisi', age=0}]

Encoding

  • ISO-8859-1 includes in addition to ASCII, it also includes text symbols corresponding to Western Europe, Greek, Thai, Arabic, and Hebrew.
  • UTF-8 variable-length character encoding for the Unicode code table
  • GB2312 Simplified Chinese
  • GBK Simplified Chinese, extended
  • BIG5 Taiwan, Traditional Chinese

character stream

public static void main(String[] args) throws Exception{
    
    
    //1. 创建FileInputStream对象
    FileInputStream fis = new FileInputStream("路径/hello.txt");
    //2. 读取
    int data = 0;
    while((data = fis.read())!=-1){
    
    
        System.out.print((char)data);
    }
    //3. 关闭
    fis.close();
}

Parent class of character stream (abstract class)

readercharacter input stream

  • public int read(){}
  • public int read(char[] c){}
  • public int read(char[] b, int off, int len){}

Writercharacter output stream

  • public void write(int n){}
  • public void write(String str){}
  • public void write(char[] c){}
//使用FileReader读取文件
public static void main(String[] args) throws Exception {
    
    
    //1. 创建FileReader 文件字符输入流
    FileReader fr = new FileReader("路径/hello.txt");
    //2. 读取
    //2.1 单个字符读取
    /*
    int data = 0;
    while ((data = fr.read()) != -1) {
        System.out.print((char) data);
    }

     */
    //2.2 字符缓冲区
    char[] buf = new char[1024];
    int count = 0;
    while((count=fr.read(buf))!=-1){
    
    
        System.out.println(new String(buf,0,count));
    }
  	//3. 关闭
    fr.close();
    System.out.println("执行完毕");
}

//使用FileWriter读取文件
public static void main(String[] args) throws Exception {
    
    
        //1. 创建FileWriter对象
        FileWriter fw = new FileWriter("/Users/xay/Desktop/编程/JAVA-FullStack/JavaSE/JavaBasics/src/Demo15/write.txt");
        //2. 写入
        for (int i = 0; i < 10; i++) {
    
    
            fw.write("java是世界上最好的语言\n");
            fw.flush();
        }
        //3. 关闭
        fw.close();
        System.out.println("执行完毕");
}

Character stream case (copy text using the above)

  • Images or binary files cannot be copied. Any file can be copied using byte streams.
  • Any file can be copied using a byte stream
  • Character streams can copy text files
public static void main(String[] args) throws Exception {
    
    
    //1. 创建FileReader FileWriter
    FileReader fr = new FileReader("路径/write.txt");
    FileWriter fw = new FileWriter("路径/write2.txt");
    //2. 读写
    int data = 0;
    while((data=fr.read())!=-1){
    
    
        fw.write(data);
        fw.flush();
    }
    //3. 关闭
    fr.close();
    fw.close();
    System.out.println("执行完毕");
}

character buffer stream

BufferedReader / BufferedWriter

Efficient reading and writing, supports input of newlines, and can write one line and read one line at a time

//BufferedReader 使用字符缓冲流读取文件
public static void main(String[] args) throws Exception{
    
    
    //创建缓冲流
    FileReader fr = new FileReader("路径/write.txt");
    BufferedReader br = new BufferedReader(fr);
    //2. 读取
    //2.1 第一种方式
    char[] buf = new char[1024];
    int count = 0;
    while((count=br.read(buf))!=-1){
    
    
        System.out.print(new String(buf,0,count));
    }
    //2.2 第二种方式，一行一行读取
    String line = null;
    while((line = br.readLine())!=null){
    
    
        System.out.println(line);
    }
    //3. 关闭
    br.close();
    System.out.println("执行结束");
}

//BufferedWriter 使用字符缓冲流写入文件
public static void main(String[] args) throws Exception{
    
    
    //1. 创建BufferedWriter对象
    FileWriter fw = new FileWriter("路径/buffer.txt");
    BufferedWriter bw = new BufferedWriter(fw);
    //2. 写入
    for(int i=0;i<10;i++){
    
    
        bw.write("好好学习，天天向上");
        bw.newLine();//换行符
        bw.flush();
    }
    //3. 关闭
    bw.close();
    System.out.println("执行完毕");
}

PrintWriter

  • The encapsulated print() / println()method supports line wrapping after writing
  • Support data printing as it is
//PrintWriter 的使用
public static void main(String[] args) throws Exception {
    
    
    //1. 创建打印流
    PrintWriter pw = new PrintWriter("路径/print.txt");
    //2. 打印
    pw.println(97);//97
    pw.println(true);//true
    pw.println(3.14);//3.14
    pw.println('a');//a
    //3. 关闭
    pw.close();
    System.out.println("执行结束");
}

Conversion flow

  • Bridge conversion flowInputStreamReader / OutputStreamWriter
  • Convert byte stream to character stream
  • Configurable character encoding method
//InputStreamReader 的使用 读取文件，指定使用的编码
public static void main(String[] args) throws Exception {
    
    
    //1. 创建InputStreamReader 对象
    FileInputStream fis = new FileInputStream("路径/write.txt");
    InputStreamReader isr = new InputStreamReader(fis,"utf-8");
    //2. 读取文件
    int data = 0;
    while((data=isr.read())!=-1){
    
    
        System.out.print((char)data);
    }
    //3. 关闭
    isr.close();
    System.out.println("执行完毕");
}

//OutputStreamWriter 写入文件，使用指定编码
public static void main(String[] args) throws Exception {
    
    
    //1. 创建OutputStreamWriter对象
    FileOutputStream fos = new FileOutputStream("路径/info.txt");
    OutputStreamWriter osw = new OutputStreamWriter(fos, "utf-8");
    //2. 写入
    for (int i = 0; i < 10; i++) {
    
    
        osw.write("你好中国");
        osw.flush();
    }
    //3. 关闭
    osw.close();
    System.out.println("执行成功");
}

File class

Concept: represents a file or folder in a physical drive letter

Use of File class

  1. delimiter
  2. File operations
  3. Folder operations

FileFilter interface

  • public interface FileFilter
    • boolean accept(File pathname)
  • When calling the listFiles() method in the File class, it supports passing in the FileFIlter interface implementation class to filter the obtained files. Only files that meet the conditions can appear in the return value of listFiles().
public class Demo01 {
    
    
    /*
File类的使用
    1. 分隔符
    2. 文件操作
    3. 文件夹操作
    */
    public static void main(String[] args) throws Exception {
    
    
        separator();
        fileOpe();
        directoryOpe();
    }

    // 1. 分隔符
    public static void separator() {
    
    
        System.out.println("路径分隔符" + File.pathSeparator);//:
        System.out.println("名称分隔符" + File.separator);///
    }

    // 2. 文件操作
    public static void fileOpe() throws Exception {
    
    
        // 1. 创建文件
        File file = new File("路径/file.txt");
        System.out.println(file.toString());
        if (!file.exists()) {
    
    
            boolean b = file.createNewFile();
            System.out.println("创建结果：" + b);//创建结果：true
        }
        // 2. 删除文件
        // 2.1 直接删除
        //System.out.println("删除的结果：" + file.delete());
        // 2.2 使用jvm退出时删除
        //ile.deleteOnExit();
        //Thread.sleep(5000);
        // 3. 获取文件信息
        System.out.println("获取绝对路径：" + file.getAbsolutePath());
        System.out.println("获取路径：" + file.getPath());
        System.out.println("获取文件名称：" + file.getName());
        System.out.println("获取父目录：" + file.getParent());
        System.out.println("获取文字长度：" + file.length());
        System.out.println("文件创建时间：" + new Date(file.lastModified()).toLocaleString());

        // 4. 判断
        System.out.println("是否可写：" + file.canWrite());
        System.out.println("是否是文件：" + file.isFile());
        System.out.println("是否隐藏：" + file.isHidden());
    }

    // 3. 文件夹操作
    public static void directoryOpe() throws Exception {
    
    
        // 1. 创建文件夹
        File dir = new File("路径/a/b/c");
        System.out.println(dir.toString());
        if (!dir.exists()) {
    
    
            //dir.mkdir();//只能创建单级目录
            boolean b = dir.mkdirs();//创建多级目录
            System.out.println("创建结果：" + b);
        }
        // 2. 删除文件夹
        // 2.1 直接删除
        //System.out.println("删除结果："+dir.delete());// 只能删除最底层空目录
        // 2.2 使用jvm删除
        //dir.deleteOnExit();

        // 3. 获取文件夹信息
        System.out.println("获取绝对路径：" + dir.getAbsolutePath());
        System.out.println("获取路径：" + dir.getPath());
        System.out.println("获取文件夹名称：" + dir.getName());//最底层文件夹名称
        System.out.println("获取父目录：" + dir.getParent());
        System.out.println("获取创建时间：" + new Date(dir.lastModified()).toLocaleString());

        // 4. 判断
        System.out.println("是否是文件夹：" + dir.isDirectory());
        System.out.println("是否隐藏：" + dir.isHidden());

        // 5. 遍历文件夹
        File dir2 = new File("路径/Demo16");
        String[] files = dir2.list();
        for(String file :files){
    
    
            System.out.println(file.toString());
        }

        // FileFilter接口的使用
        File[] files2 = dir2.listFiles(new FileFilter() {
    
    
            @Override
            public boolean accept(File pathname) {
    
    
                if(pathname.getName().endsWith(".txt")){
    
    
                    return true;
                }
                return false;
            }
        });
        for(File file : files2){
    
    
            System.out.println(file.getName());
        }
    }
}

Traverse folders recursively

//递归遍历文件夹
public static void main(String[] args) throws Exception {
    
    
    listDir(new File("/Users/xay/Desktop/编程/JAVA-FullStack/JavaSE/JavaBasics/src"));
}

public static void listDir(File dir) {
    
    
    File[] files = dir.listFiles();
    System.out.println(dir.getName());
    if (files != null && files.length > 0) {
    
    
        for(File file : files){
    
    
            if(file.isDirectory()){
    
    
                listDir(file);
            }else {
    
    
                System.out.println(file.getName());
            }
        }
    }
}

Delete folders recursively

public static void deleteDir(File dir){
    
    
    File[] files = dir.listFiles();
    if(files!=null && files.length>0){
    
    
        for(File file : files){
    
    
            if(file.isDirectory()){
    
    
                deleteDir(file);
            }else {
    
    
                //删除文件
                System.out.println(file.getAbsolutePath()+"删除"+file.delete());
            }
        }
    }
    System.out.println(dir.getAbsolutePath()+"删除"+dir.delete());
}

Properties

  • Properties: property collection
  • Features
    1. Store attribute names and attribute values
    2. The attribute name and attribute value are both string types.
    3. no generics
    4. related to flow
//Properties集合的使用
public static void main(String[] args) throws Exception{
    
    
    //1. 创建集合
    Properties properties = new Properties();
    //2. 添加数据
    properties.setProperty("username","zhangsan");
    properties.setProperty("age","20");
    System.out.println(properties.toString());
    //3. 遍历
    //3.1 keyset
    //3.2 entrySet
    //3.3 stringPropertyNames()
    Set<String> pronames = properties.stringPropertyNames();
    for(String pro : pronames){
    
    
        System.out.println(pro + "-" + properties.get(pro));
    }

    //和流有关的方法
    //4.1 list方法
    PrintWriter pw =new PrintWriter("路径/print.txt");
    properties.list(pw);
    pw.close();
    //4.2 store方法 保存
    FileOutputStream fos = new FileOutputStream("路径/print.properties");
    properties.store(fos,"注释");
    fos.close();
    //4.3 load方法 加载
    Properties properties2 = new Properties();
    FileInputStream fis = new FileInputStream("路径/print.properties");
    properties2.load(fis);
    fis.close();
    System.out.println(properties2.toString());
}

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