io流实现对.txt文件的增删改查操作（文件中某一行内容的增加删除修改）-编程知识

一、要求

二、完整代码

三、结果演示

四、增删改查代码分析

一、要求

我们需要利用io流对.txt文件中某行或者某几行内容进行增加、删除、修改操作，查看文件全部内容。

使用的类：

File

FileRead -- BufferedReader

FileWriter -- BufferedWriter

二、完整代码

Books:类

package com.nanchu;import java.io.*;
import java.util.ArrayList;
import java.util.Scanner;/*** @Author 南初* @Create 2024/2/29 8:44* @Version 1.0*/
public class Books {private String bookName;private String bookPrice;private String bookNum;Scanner scan = new Scanner(System.in);// 添加图书public void addBook(File file) throws IOException {BufferedReader bufferedReader =  new BufferedReader(new FileReader(file));ArrayList<String> strb = new ArrayList<>();System.out.print("\n请输入图书名：");String name = scan.next();System.out.print("\n请输入图书价格：");String price = scan.next();System.out.print("\n请输入图书数量：");String num = scan.next();String addBook =name+","+price+","+num;String line =null;while((line = bufferedReader.readLine())!=null){strb.add(line);}strb.add(addBook);BufferedWriter bw = new BufferedWriter(new FileWriter(file));;for(String info:strb){bw.write(info);bw.newLine();}// 关闭文件流bw.flush();bw.close();bufferedReader.close();System.out.println("添加图书成功！");}// delete 删除图书public void deleteBook(File file) throws IOException {BufferedReader bufferedReader = new BufferedReader(new FileReader(file));ArrayList<String> strb = new ArrayList<>();System.out.println("请输入删除图书序号：");int bookID=scan.nextInt();  //修改图书序号String line = null;while((line = bufferedReader.readLine())!=null){strb.add(line);}int x = strb.size();while(true){if (bookID >= 0 &&bookID < x) {break;}else {System.out.println("输入错误,请重新输入删除图书序号：");bookID=scan.nextInt();  //修改图书序号}}System.out.println(strb.get(bookID));// 集合中删除图书strb.remove(bookID);BufferedWriter bw = new BufferedWriter(new FileWriter(file));for(String info :strb){bw.write(info);bw.newLine();}System.out.println("删除图书成功！");bw.flush();bw.close();bufferedReader.close();}// 修改图书public void alterBook(File file) throws IOException {BufferedReader bufferedReader = new BufferedReader(new FileReader(file));ArrayList<String> strb = new ArrayList<>();String line = null;int count=0;System.out.print("请输入修改图书序号:");int bookID=scan.nextInt();  //修改图书序号while((line = bufferedReader.readLine())!=null){if(count == bookID){String[] strings = line.split(",");System.out.print("\n请输入图书名：");String name = scan.next();strings[0] = name;System.out.print("\n请输入图书价格：");String price = scan.next();strings[1] = price;System.out.print("\n请输入图书数量：");String num = scan.next();strings[2] = num;line =String.join(",", strings);strb.add(line);System.out.println("修改图书成功！");}else {strb.add(line);}count++;}BufferedWriter bw = new BufferedWriter(new FileWriter(file));for(String info: strb){bw.write(info);bw.newLine();}bw.flush();bw.close();bufferedReader.close();}//  查看所有图书public void viewAllBook(File file) throws IOException {System.out.println("序号\t\t\t书名\t\t\t价格\t\t\t数量");BufferedReader bufferedReader = new BufferedReader(new FileReader(file));String line = null;for(int i=0;(line=bufferedReader.readLine())!=null;i++){String[] strings = line.split(",");System.out.print(i +"\t\t\t");for(int j=0;j<strings.length;j++){System.out.print(strings[j]+"\t\t\t");}System.out.print("\n");}bufferedReader.close();}}

ioFile类：

package com.nanchu;import java.io.*;
import java.util.Scanner;/*** @Author 南初* @Create 2024/2/29 8:36* @Version 1.0*/
public class IoFile {public static void main(String[] args) {File file = new File("E:\\Java Code base\\FoodOrderingSystem\\src\\com\\nanchu\\test.txt");Books books = new Books();Scanner scan = new Scanner(System.in);while(true) {System.out.println("------请选择你的操作------");System.out.println("1.增   2.删   3.改   4.查   5.退出");System.out.print("请选择你需要的操作(这里默认输入除了1234之外的数字认为是退出)：");int num = scan.nextInt();if (num == 1) {// 增try {books.addBook(file);} catch (IOException e) {throw new RuntimeException(e);}} else if (num==2) {// 删try {books.deleteBook(file);} catch (IOException e) {throw new RuntimeException(e);}} else if (num==3) {// 改try {books.alterBook(file);} catch (IOException e) {throw new RuntimeException(e);}} else if (num==4) {// 查try {books.viewAllBook(file);} catch (IOException e) {throw new RuntimeException(e);}}else {break;}}System.out.println("运行结束！");}
}

test.txt

C,50.0,30
Java,40.0,50
Go,50.0,20

三、结果演示

增加操作：

test.txt文件查看增加成功：

删除操作：

test.txt文件查看删除成功：

修改数据操作：

test.txt文件查看修改成功：

四、增删改查代码分析

增删改思想：

1. 将 .txt 文件内容全部读取出来

2. 创建ArrayList集合储存读取出来的内容

3. 针对需要修改的某行或者或几行内容从ArrayList集合中取出进行增删改操作

4. 创建BufferedWriter 对象传入(new FileWriter(file)) ,而不是(new FileWriter(file,true)) 因为不需要将内容追加，增加true，意思是在原文件内容后面追加新内容，我们这里做的是将储存的内容写入到文件中，需要的是原文件的空白文件，不加true意思是覆盖已有的文件。

5. 关闭流

对于输出流来说，File类的对象是可以不存在的。
> 如果File类的对象不存在，则可以在输出的过程中，自动创建File类的对象
> 如果File类的对象存在，
> 如果调用FileWriter(File file)或FileWriter(File file,false)，输出时会新建File文件覆盖已有的文件
> 如果调用FileWriter(File file,true)构造器，则在现有的文件末尾追加写出内容。

增：

Scanner scan = new Scanner(System.in);// 添加图书public void addBook(File file) throws IOException {BufferedReader bufferedReader =  new BufferedReader(new FileReader(file));ArrayList<String> strb = new ArrayList<>();System.out.print("\n请输入图书名：");String name = scan.next();System.out.print("\n请输入图书价格：");String price = scan.next();System.out.print("\n请输入图书数量：");String num = scan.next();String addBook =name+","+price+","+num;String line =null;while((line = bufferedReader.readLine())!=null){strb.add(line);}strb.add(addBook);BufferedWriter bw = new BufferedWriter(new FileWriter(file));;for(String info:strb){bw.write(info);bw.newLine();}// 关闭文件流bw.flush();bw.close();bufferedReader.close();System.out.println("添加图书成功！");}

删：

    Scanner scan = new Scanner(System.in);// delete 删除图书public void deleteBook(File file) throws IOException {BufferedReader bufferedReader = new BufferedReader(new FileReader(file));ArrayList<String> strb = new ArrayList<>();System.out.println("请输入删除图书序号：");int bookID=scan.nextInt();  //修改图书序号String line = null;while((line = bufferedReader.readLine())!=null){strb.add(line);}int x = strb.size();while(true){if (bookID >= 0 &&bookID < x) {break;}else {System.out.println("输入错误,请重新输入删除图书序号：");bookID=scan.nextInt();  //修改图书序号}}System.out.println(strb.get(bookID));// 集合中删除图书strb.remove(bookID);BufferedWriter bw = new BufferedWriter(new FileWriter(file));for(String info :strb){bw.write(info);bw.newLine();}System.out.println("删除图书成功！");bw.flush();bw.close();bufferedReader.close();}

改：

Scanner scan = new Scanner(System.in);
// 修改图书
public void alterBook(File file) throws IOException {BufferedReader bufferedReader = new BufferedReader(new FileReader(file));ArrayList<String> strb = new ArrayList<>();String line = null;int count=0;System.out.print("请输入修改图书序号:");int bookID=scan.nextInt();  //修改图书序号while((line = bufferedReader.readLine())!=null){if(count == bookID){String[] strings = line.split(",");System.out.print("\n请输入图书名：");String name = scan.next();strings[0] = name;System.out.print("\n请输入图书价格：");String price = scan.next();strings[1] = price;System.out.print("\n请输入图书数量：");String num = scan.next();strings[2] = num;line =String.join(",", strings);strb.add(line);System.out.println("修改图书成功！");}else {strb.add(line);}count++;}BufferedWriter bw = new BufferedWriter(new FileWriter(file));for(String info: strb){bw.write(info);bw.newLine();}bw.flush();bw.close();bufferedReader.close();
}

查：

Scanner scan = new Scanner(System.in);
//  查看所有图书
public void viewAllBook(File file) throws IOException {System.out.println("序号\t\t\t书名\t\t\t价格\t\t\t数量");BufferedReader bufferedReader = new BufferedReader(new FileReader(file));String line = null;for(int i=0;(line=bufferedReader.readLine())!=null;i++){String[] strings = line.split(",");System.out.print(i +"\t\t\t");for(int j=0;j<strings.length;j++){System.out.print(strings[j]+"\t\t\t");}System.out.print("\n");}bufferedReader.close();
}