Java EE Basics (22)/io stream

1. IO stream (Sequence stream)

• 1. What is a sequence stream
  • The sequence stream can integrate multiple byte input streams into one, reading from the sequence stream, starting with the first stream being consolidated, reading one after the second, and so on.

• 2. How to use

  • Integration of two: Sequenceinputstream (InputStream, InputStream)

  • FileInputStream fis1 = new FileInputStream("a.txt");            //创建输入流对象,关联a.txtFileInputStream fis2 = new FileInputStream("b.txt");            //创建输入流对象,关联b.txtSequenceInputStream sis = new SequenceInputStream(fis1, fis2);  //将两个流整合成一个流FileOutputStream fos = new FileOutputStream("c.txt");           //创建输出流对象,关联c.txtint b;while((b = sis.read()) != -1) {                                 //用整合后的读    fos.write(b);                                               

2, IO Stream (Sequence Flow consolidation multiple)

• Consolidate multiple: Sequenceinputstream (enumeration)

• FileInputStream fis1 = new FileInputStream("a.txt");    //创建输入流对象,关联a.txtFileInputStream fis2 = new FileInputStream("b.txt");    //创建输入流对象,关联b.txtFileInputStream fis3 = new FileInputStream("c.txt");    //创建输入流对象,关联c.txtVector<InputStream> v = new Vector<>();                 //创建vector集合对象v.add(fis1);                                            //将流对象添加v.add(fis2);v.add(fis3);Enumeration<InputStream> en = v.elements();             //获取枚举引用SequenceInputStream sis = new SequenceInputStream(en);  //传递给SequenceInputStream构造FileOutputStream fos = new FileOutputStream("d.txt");int b;while((b = sis.read()) != -1) {    fos.write(b);}sis.close();fos.close();

3. Io stream (Memory output stream * * * * *)

• 1. What is a memory output stream
  • The output stream can write data to memory, memory as a buffer, write out once you can get all the data at once

• 2. How to use

  • Create object: New Bytearrayoutputstream ()
  • Write Data: Write (int), write (byte[])
  • Get data: Tobytearray ()

  • FileInputStream fis = new FileInputStream("a.txt");ByteArrayOutputStream baos = new ByteArrayOutputStream();int b;while((b = fis.read()) != -1) {    baos.write(b);}//byte[] newArr = baos.toByteArray();               //将内存缓冲区中所有的字节存储在newArr中//System.out.println(new String(newArr));System.out.println(baos);fis.close();

4, IO stream (memory output stream of Black Horse interview questions)

• Define a file input stream and call the Read (byte[] b) method to print the contents of the A.txt file (byte array size limit is 5)

•     FileInputStream fis = new FileInputStream("a.txt");             //创建字节输入流,关联a.txt    ByteArrayOutputStream baos = new ByteArrayOutputStream();       //创建内存输出流    byte[] arr = new byte[5];                                       //创建字节数组,大小为5    int len;    while((len = fis.read(arr)) != -1) {                            //将文件上的数据读到字节数组中        baos.write(arr, 0, len);                                    //将字节数组的数据写到内存缓冲区中    }    System.out.println(baos);                                       //将内存缓冲区的内容转换为字符串打印    fis.close();

5. Io Stream (Object operation Flow objecoutputstream)

• 1. What is an object manipulation flow
  • The stream can write out an object, or read an object into the program. That is, the operation of serialization and deserialization is performed.

• 2. How to use

  • Written: New ObjectOutputStream (OutputStream), WriteObject ()

    public class Demo3_ObjectOutputStream {    /**     * @param args     * @throws IOException      * 将对象写出,序列化     */    public static void main(String[] args) throws IOException {        Person p1 = new Person("张三", 23);        Person p2 = new Person("李四", 24);//      FileOutputStream fos = new FileOutputStream("e.txt");//      fos.write(p1);//      FileWriter fw = new FileWriter("e.txt");//      fw.write(p1);        //无论是字节输出流,还是字符输出流都不能直接写出对象        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("e.txt"));//创建对象输出流        oos.writeObject(p1);        oos.writeObject(p2);        oos.close();    }}

6. Io Stream (Object operation Flow ObjectInputStream)

• READ: New ObjectInputStream (InputStream), ReadObject ()

  • public class Demo3_ObjectInputStream {    /**     * @param args     * @throws IOException      * @throws ClassNotFoundException      * @throws FileNotFoundException      * 读取对象,反序列化     */    public static void main(String[] args) throws IOException, ClassNotFoundException {        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("e.txt"));        Person p1 = (Person) ois.readObject();        Person p2 = (Person) ois.readObject();        System.out.println(p1);        System.out.println(p2);        ois.close();    }}

7. Io Stream (object operation flow optimization)

* Write objects stored in the collection

Person p1 = new Person("张三", 23);Person p2 = new Person("李四", 24);Person p3 = new Person("马哥", 18);Person p4 = new Person("辉哥", 20);ArrayList<Person> list = new ArrayList<>();list.add(p1);list.add(p2);list.add(p3);list.add(p4);ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("f.txt"));oos.writeObject(list);                                  //写出集合对象oos.close();

• The read is a collection object

  ObjectInputStream ois = new ObjectInputStream(new FileInputStream("f.txt"));    ArrayList<Person> list = (ArrayList<Person>)ois.readObject();   //泛型在运行期会被擦除,索引运行期相当于没有泛型                                                                    //想去掉黄色可以加注解                    @SuppressWarnings("unchecked")    for (Person person : list) {        System.out.println(person);    }ois.close();

8. IO stream (plus ID number)

• Attention
  • The object to be written must implement the serializable interface to be serialized
  • No need to add ID number

9. Io Stream (Overview and features of the print stream)

• 1. What is a print stream

  • This flow makes it easy to output the ToString () result of an object, and automatically adds line breaks, and can use the auto-brushed pattern

  • System.out is a printstream, which outputs information to the console by default

    PrintStream ps = System.out;ps.println(97);                 //其实底层用的是Integer.toString(x),将x转换为数字字符串打印ps.println("xxx");ps.println(new Person("张三", 23));Person p = null;ps.println(p);                  //如果是null,就返回null,如果不是null,就调用对象的toString()

• 2. How to use

  • Printed: Print (), println ()
  • Auto-Brushed: PrintWriter (OutputStream out, Boolean autoflush, String encoding)

  • The print flow operates only for data purposes

    PrintWriter pw = new PrintWriter(new FileOutputStream("g.txt"), true);pw.write(97);pw.print("大家好");pw.println("你好");               //自动刷出,只针对的是println方法pw.close();

10. Io Stream (Overview of standard input and output streams and output statements)

• 1. What is the standard input/output stream (Master)
  • System.in is InputStream, standard input stream, which reads byte data from keyboard input by default
  • System.out is the PrintStream, standard output stream, which can output character and byte data to the console by default

• 2. Modify the standard input/output stream (Learn)

  • Modify input stream: System.setin (InputStream)
  • Modify output stream: System.setout (PrintStream)

  • System.setIn(new FileInputStream("a.txt"));             //修改标准输入流System.setOut(new PrintStream("b.txt"));                //修改标准输出流InputStream in = System.in;                             //获取标准输入流PrintStream ps = System.out;                            //获取标准输出流int b;while((b = in.read()) != -1) {                          //从a.txt上读取数据    ps.write(b);                                        //将数据写到b.txt上}in.close();ps.close();

11. IO Stream (Modify standard input and output stream copy picture)

    System.setIn(new FileInputStream("IO图片.png"));      //改变标准输入流    System.setOut(new PrintStream("copy.png"));         //改变标准输出流    InputStream is = System.in;                         //获取标准输入流    PrintStream ps = System.out;                        //获取标准输出流    int len;    byte[] arr = new byte[1024 * 8];    while((len = is.read(arr)) != -1) {        ps.write(arr, 0, len);    }    is.close();    ps.close();

11, Io Stream (two ways to achieve keyboard input)

• The ReadLine method of A:bufferedreader.
  • BufferedReader br = new BufferedReader (new InputStreamReader (system.in));
• B:scanner

12. Io Stream (Overview of random access streams and read and write data)

• A: Overview of random access streams

  • Randomaccessfile Overview
  • The Randomaccessfile class does not belong to a stream and is a subclass of the object class. But it incorporates the functions of InputStream and OutputStream.
  • Supports read and write to random access files.

• B:read (), write (), Seek ()

13. IO Stream (data input/output stream)

• 1. What is a data input/output stream
  • DataInputStream, DataOutputStream can read and write data according to the basic data type size
  • For example, write a number on a long size that is 8 bytes when it is written out. Reads can also be read by a long type, read 8 bytes at a time.

• 2. How to use

  • DataOutputStream (OutputStream), Writeint (), Writelong ()

    DataOutputStream dos = new DataOutputStream(new FileOutputStream("b.txt"));dos.writeInt(997);dos.writeInt(998);dos.writeInt(999);dos.close();

  • DataInputStream (InputStream), ReadInt (), Readlong ()

    DataInputStream dis = new DataInputStream(new FileInputStream("b.txt"));int x = dis.readInt();int y = dis.readInt();int z = dis.readInt();System.out.println(x);System.out.println(y);System.out.println(z);dis.close();

14. Io Stream (Overview of the properties and use as a map collection)

• Overview of A:properties
  • The Properties class represents a persistent set of attributes.
  • Properties can be saved in a stream or loaded from a stream.
  • Each key and its corresponding value in the property list is a string.
• B: Case Demo
  • Properties as the use of the map collection

15. IO Stream (special function of properties use)

• Special features of A:properties
  • Public Object setProperty (String key,string value)
  • public string GetProperty (string key)
  • Public enumeration Stringpropertynames ()
• B: Case Demo
  • Special features of properties

16. IO Stream (Load () and store () function of properties)

• A:properties load () and store () functions
• B: Case Demo
  • The load () and store () functions of the properties

Java EE Basics (22)/io stream