【210天】黑馬程序員27天視頻學習筆記【Day22-上】

時間 2019-12-07

原文原文鏈接

叨逼叨兩句

快樂來的越容易，痛苦也就會來的越頻繁。java

若是沒有互聯網，也許你這輩子真就受困於你身邊圈子的認知了。面試

22-(01-02):序列流（整合兩個流對象+整合多個流對象）

序列流的存在價值是：幫助整合多個文件的內容放到一個文件中。數組
整合多個時，須要使用枚舉的方式。優化

package com.test.demo001;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.SequenceInputStream;
import java.util.Enumeration;
import java.util.Vector;

public class Demo010 {
    public static void main(String[] args) throws IOException {
        //demo01();
        //demo02();
        demo03();
        
    }

    private static void demo03() throws FileNotFoundException, IOException {
        FileInputStream fis1 = new FileInputStream("a.txt");
        FileInputStream fis2 = new FileInputStream("b.txt");
        FileInputStream fis3 = new FileInputStream("c.txt");
        
        Vector<InputStream> v = new Vector<>();  //建立Vector集合對象
        v.add(fis1);
        v.add(fis2);
        v.add(fis3);
        Enumeration<InputStream> en = v.elements();//獲取枚舉引用
        SequenceInputStream sis = new SequenceInputStream(en);
        FileOutputStream fos = new FileOutputStream("o.txt");
        int a;
        while((a = sis.read())!= -1){
            fos.write(a);
        }
        sis.close();
        fos.close();
    }

    private static void demo02() throws FileNotFoundException, IOException {
        FileInputStream fis1 = new FileInputStream("a.txt");
        FileInputStream fis2 = new FileInputStream("b.txt");
        FileInputStream fis3 = new FileInputStream("c.txt");
        
        SequenceInputStream sis = new SequenceInputStream(fis1,fis2);//只能整合兩個流對象
        FileOutputStream fos = new FileOutputStream("o.txt");
        
        int a;
        while((a = sis.read())!= -1){
            fos.write(a);
        }
        
        sis.close();
        fos.close();
    }

    private static void demo01() throws FileNotFoundException, IOException {
        FileInputStream fis1 = new FileInputStream("a.txt");
        FileOutputStream fos = new FileOutputStream("o.txt");
        
        int a;
        while((a = fis1.read())!= -1){
            fos.write(a);
        }
        fis1.close();
        
        FileInputStream fis2 = new FileInputStream("b.txt");
        int b;
        while((b = fis2.read())!= -1){
            fos.write(b);
        }
        fis2.close();
        
        FileInputStream fis3 = new FileInputStream("c.txt");
        int c;
        while((c = fis3.read())!= -1){
            fos.write(c);
        }
        fis3.close();
        
        fos.close();
    }
}

22-03：內存輸出流

概述

該輸出流能夠向內存中寫入數據，它是把內存做爲一個緩衝區，寫出以後一次性將數據取出，經常使用於聊天應用。編碼
數組和集合在內存中用完就自動釋放了，不像流，跟硬盤有關聯，須要手動關閉。code

使用方式

建立對象：new ByteArrayOutputStream()對象
寫出數據：write(int),write(byte[])接口
獲取數據：toByteArray()遊戲

private static void demo01() throws FileNotFoundException, IOException {
        FileInputStream fis = new FileInputStream("a.txt");
        ByteArrayOutputStream baos = new ByteArrayOutputStream();//在內存中建立了能夠增加的內存數組
        
        int a;
        while((a = fis.read())!= -1){
            baos.write(a);            //將讀取到的數據逐個寫到內存中
        }
        
        fis.close();
        
        //這種方式能夠指定轉換數組的編碼
//        byte[] arr = baos.toByteArray();           //將緩衝區的數據所有獲取出來，並賦值給arr數組
//        System.out.println(new String(arr));
        
        //這種方式使用的是平臺默認的編碼表
        System.out.println(baos);
        
    }

22-04：內存輸出流之黑馬面試題

FileInputStream讀取中文時出現亂碼的解決方案：內存
1. 字符流
2. 內存輸出流：ByteArrayOutputStream

package com.test.demo001;

import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.IOException;

public class Demo010 { 
    public static void main(String[] args) throws IOException {
        FileInputStream fis = new FileInputStream("d.txt");
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        byte[] arr = new byte[5];
        int len;
        while((len = fis.read(arr))!= -1){
            baos.write(arr,0,len);
        }
        System.out.println(baos);
        fis.close();
    }
}

22-(05-08)

對象操做流ObjectOutputStream（序列化、存檔）

序列化：將對象寫到文件上【相似遊戲存檔】
反序列化：將對象從文件中讀取出來【相似遊戲讀檔】
對象寫到文件上會是亂碼，但木有關係，能讀出來就行。
對象必須是可序列化的，即它必須實現Serializeable接口
Serializeable接口中沒有任何方法，它就是一個標記而已
若本身不指定，則類的ID號是隨機的

package com.test.demo001;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;

public class Demo010 {
    public static void main(String[] args) throws IOException {
        Student s1 = new Student("z3",23);
        Student s2 = new Student("l4",24);
        FileOutputStream fos = new FileOutputStream("k.txt");
        ObjectOutputStream oos = new ObjectOutputStream(fos);
        oos.writeObject(s1);
        oos.writeObject(s2);
        fos.close();
        oos.close();
        
    }
}

對象操做流ObjectInputStream（反序列化、讀檔）

package com.test.demo001;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.ObjectInputStream;

public class Demo011 {
    public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("k.txt"));
        Student s1 = (Student) ois.readObject();
        Student s2 = (Student) ois.readObject();
        //Student s3 = (Student) ois.readObject(); //當文件讀到末尾出現EOFException
        System.out.println(s1);
        System.out.println(s2);
    }
}

對象操做流優化

序列化

package com.test.demo001;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;
import java.util.ArrayList;

public class Demo010 {
    public static void main(String[] args) throws IOException{
        Student s1 = new Student("z3",23);
        Student s2 = new Student("z4",24);
        Student s3 = new Student("z5",25);
        Student s4 = new Student("z6",26);
        ArrayList<Student> list = new ArrayList<>(); 
        list.add(s1);
        list.add(s2);
        list.add(s3);
        list.add(s4);
        ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("test.txt"));
        oos.writeObject(list); //將集合對象一次寫入
        oos.close();
    }
}

反序列化

package com.test.demo001;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.util.ArrayList;

public class Demo011 {
    public static void main(String[] args) throws IOException, ClassNotFoundException{
        ObjectInputStream ois = new ObjectInputStream(new FileInputStream("test.txt"));
        ArrayList<Student> list = (ArrayList<Student>) ois.readObject(); //將集合對象一次讀取
        for (Student stu : list) {
            System.out.println(stu);
        }
        ois.close();
        
    }
}