//将图书信息封装成一个实体类

public class Books{

    int id;

    String name;

    String publish;

    double price;

    double money;

    int number;

    public Books(int id, String name, String publish, double price,

            int number, double money){

        this.id = id;

        this.name = name;

        this.publish = publish;

        this.price = price;

        this.number = number;

        this.money = money;

    }

    //toString()将任何对象转换成字符串表达形式

    @Override

    public String toString(){

        String message = "图书编号：" + id + " 图书名称：" + name +

                " 出版社：" + publish + " 单价 " + price + " 库存数量：" + number;

        return message;

    }

    public void setNum(int number){

        this.number = number;

    }

}

import java.util.*;

public class RecordBooksOrder{

    //static关键字来修饰成员变量，该变量被称为静态变量，静态变量被所有实例共享

    static ArrayList<Books> booksList = new ArrayList<Books>();

    public static void main(String[] args){

        //初始化书架

        init();

        //将书架上所有图书信息打印出来

        for(int i=0; i<booksList.size(); i++){

            System.out.println(booksList.get(i));

        }

        while(true){

            //获取控制台信息

            Scanner scan = new Scanner(System.in);

            System.out.println("请输入图书编号：");

            int bookId = scan.nextInt();

            Books stockBooks = getBooksById(bookId);

            if(stockBooks != null){

                System.out.println("当前图书信息：");

                System.out.println(stockBooks);

                System.out.println("请输入当前购买数量：");

                int bookNumber = scan.nextInt();

                if(bookNumber <= stockBooks.number){

                    //将输入信息封装成Books对象

                    Books sellBook = new Books(stockBooks.id, stockBooks.name,

                        stockBooks.publish, stockBooks.price, bookNumber,

                        bookNumber*stockBooks.price);

                    //将本条数据保存至本地文件

                    FileUtil.saveBooks(sellBook);

                    stockBooks.setNum(stockBooks.number-bookNumber);

                }else{

                    System.out.println("库存不足！");

                }

            }else{

                    System.out.println("图书编码输入错误误！");

             }

        }

    }

    private static void init(){

        Books book1 = new Books(101, "python", "北邮出版社", 44.50, 100, 4450);

        Books book2 = new Books(102, "java", "清华出版社", 30, 50, 1500);

        Books book3 = new Books(103, "c++", "人民邮电出版社", 90, 100, 9000);

        booksList.add(book1);

        booksList.add(book2);

        booksList.add(book3);

        //System.out.println(book1.id);

    }

    private static Books getBooksById(int bookId){

        for(int i=0; i<booksList.size(); i++){

            //System.out.println(bookId);

            Books book = booksList.get(i);

            if(book.id == bookId){

                return book;

            }

        }

        return null;

    }

}

import java.util.*;

import java.text.*;

import java.io.*;

public class FileUtil{

    //被final修饰的变量称为常量，一旦被赋值，其值不能被改变

    public static final String SEPARATE_FIELD = ",";

    public static final String SEPARATE_LINE = "\r\n";

    public static void saveBooks(Books sellBook){

        //创建文件名

        Date date = new Date();

        //parse()返回的是一个Date类型数据，format()返回的是一个StringBuffer类型的数据

        DateFormat format = new SimpleDateFormat("yyyyMMdd");

        String name = "sell_log" + format.format(date) + ".csv";

        InputStream in = null;

        //判断本地是否有此文件

        try{

            //这句话执行，如果没有该文件，会抛出FileNotFoundException异常

            in = new FileInputStream(name);

            if(in != null){

                //存在文件，采取修改文件的方式

                in.close();

                createFile(name, true, sellBook);

            }

        } catch (FileNotFoundException e){

            //不存在该文件，应创建文件

            createFile(name, false, sellBook);

        } catch (IOException e){

            e.printStackTrace();

        }

    }

    //label=true:存在文件

    public static void createFile(String name, boolean label, Books sellBook){

        BufferedOutputStream bos = null;

        StringBuffer sbf = new StringBuffer();

        try{

            if(label){

                bos = new BufferedOutputStream(new FileOutputStream(name, true));

            }else{

                bos = new BufferedOutputStream(new FileOutputStream(name));

                String[] str = new String[] {"图书编号", "图书名称", "购买数量",

                        "单价", "总价", "出版社"};

                for(String s : str){

                    sbf.append(s + SEPARATE_FIELD);

                }

            }

            sbf.append(SEPARATE_LINE);

            sbf.append(sellBook.id).append(SEPARATE_FIELD);

            sbf.append(sellBook.name).append(SEPARATE_FIELD);

            sbf.append(sellBook.number).append(SEPARATE_FIELD);

            sbf.append(sellBook.price).append(SEPARATE_FIELD);

            sbf.append(sellBook.money).append(SEPARATE_FIELD);

            sbf.append(sellBook.publish).append(SEPARATE_FIELD);

            String str = sbf.toString();

            byte[] b = str.getBytes();

            for (int i=0; i<b.length; i++){

                bos.write(b[i]);

            }

        } catch(Exception e){

            e.printStackTrace();

        } finally{

            try {

                if(bos!=null)

                    bos.close();

            }catch(Exception e2){

                e2.printStackTrace();

            }

        }

    }

}