笔记 第1章 流与文件(4) 把对象存储到文件

 1.2.3 以文本格式存储对象

可使用特殊形式进行存储对象数据，比如json格式 {"a":"b","c":[1,2,3]},或者xml,<v><a>b<a><c><1><2><3><c><v>,或者自定义格式，如指定分割符，可考虑使用序列化相关的方法完成读入，写出方法的拦截，从而实现自定义的效果。

readObject:将数据写入流

writeObject:将数据从流读出

作者示例：把对象写入文件

相比原文略有改动，close()写在了finally

TestFileTest.java

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import java.io.FileReader;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;
 
public class TestFileTest {
    public static void main(String[] args) {
        Employee[] staff = new Employee[3];
         
        staff[0] = new Employee("Carl Cracker", 75000,1987, 12, 15);
        staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
        staff[2] = new Employee("Tony Tester", 40000, 1990, 3, 15);
 
        PrintWriter out = null;
        Scanner in = null;
        try{
            out = new PrintWriter("employee.dat");
            writeData(staff, out);
             
            in = new Scanner(new FileReader("employee.dat"));
            Employee[] newStaff = readData(in);
            for(Employee e:newStaff){
                System.out.println(e);
            }
        }catch (IOException e){
            e.printStackTrace();
        }finally {
            if(out!=null){
                out.close();
            }
             
            if(in!=null){
                in.close();
            }
        }
    }
     
    private static void writeData(Employee[] employees, PrintWriter out) throws IOException{
        out.println(employees.length);
        for(Employee e:employees){
            e.writeData(out);
        }
    }
     
    private static Employee[] readData(Scanner in){
        int n = in.nextInt();
        in.nextLine();
         
        Employee[] employees = new Employee[n];
        for(int i = 0; i < n; i++){
            employees[i] = new Employee();
            employees[i]. readData(in);
        }
        return employees;
    }
}

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Employee.java

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import java.io.PrintWriter;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.Scanner;
 
public class Employee {
    private String name;
    private double salary;
    private Date hireDay;
    public Employee(){}
 
    public Employee(String n, double s, int year, int month, int day){
        name = n;
        salary = s;
        GregorianCalendar calendar = new GregorianCalendar(year,month-1, day);
        hireDay = calendar.getTime();
    }
 
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public double getSalary() {
        return salary;
    }
 
    public void setSalary(double salary) {
        this.salary = salary;
    }
 
    public Date getHireDay() {
        return hireDay;
    }
 
    public void setHireDay(Date hireDay) {
        this.hireDay = hireDay;
    }
 
    public void raiseSalary(double byPercent){
        double raise = salary*byPercent/100;
        salary+=raise;
    }
 
    @Override
    public String toString() {
        return getClass().getName() + "[name="+name+",salary="+salary+",hireDay="+hireDay+"]";
 
    }
 
    public void writeData(PrintWriter out){
        GregorianCalendar calendar = new GregorianCalendar();
        calendar.setTime(hireDay);
        out.println(name+"|"+salary+"|"+calendar.get(Calendar.YEAR)+"|"+(calendar.get(Calendar.MONTH)+1)+"|"+
                calendar.get(Calendar.DAY_OF_MONTH));
    }
 
    public void readData(Scanner in){
        String line = in.nextLine();
        String[] tokens = line.split("\\|");
        name = tokens[0];
        salary = Double.parseDouble(tokens[1]);
        int y = Integer.parseInt(tokens[2]);
        int m = Integer.parseInt(tokens[3]);
        int d = Integer.parseInt(tokens[4]);
 
        GregorianCalendar calendar = new GregorianCalendar(y, m-1, d);
        hireDay = calendar.getTime();
    }
}

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运行结果：

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 1.2.4 字符集

字符保存在文件中有各种格式，比较常用的有 ISO-8899-1,UTF-8,如果大概记得，不太确定是否有横线，可以查看 StandardCharsets 确定：

如果不在这里面（不常见），可以查看IDEA右下角的more:

来确定具体的名字有无横线，或者也可以用 Charset.isSupported(别名) 确定是否书写正确。输出所有系统字符，因为太多了，为了一屏能显示完，一行放100长度：

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public class Main {
    public static void main(String[] args){
        Map<String,Charset> map = Charset.availableCharsets();
        int len = 0;
        for(String charsetName:map.keySet()){
            len += charsetName.length();
            if(len >= 100){
                len = 0;
                System.out.println();
                len = charsetName.length()+1;
            }
            len += 1;
            System.out.print(charsetName);
            System.out.print(" ");
        }
    }
}

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运行结果：

🚗🚓🚕🛺🚙🚌🚐🚎🚑🚒🚚🚛🚜🚘🚔🚖🚍🦽🦼🛹🚲🛴🛵🏍

🚗🚓🚕🛺🚙🚌🚐🚎🚑🚒🚚🚛🚜🚘🚔🚖🚍🦽🦼🛹🚲🛴🛵🏍

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