为什么不能正确解析我的数组元素？

Question

Java 新手，我正在学习 InputStream class 并尝试实现我在 Cay S. Horstmann 的核心 Java 第 II 卷第 10 版中找到的代码。此代码应该显示 Input/OutputStream classes 在通过将数据从数组保存和读取到文件中来读取字节序列时是如何有用的。它以给定字符串和 int 数字的数组声明开始，将此数组的元素保存在 .dat 文件中，从 .dat 文件中读取元素并将它们显示在控制台中。

但我在控制台中得到了这个：

Exception in thread "main" java.time.format.DateTimeParseException: Text '0' could not be parsed at index 0
    at java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:1949)
    at java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1851)
    at java.time.LocalDate.parse(LocalDate.java:400)
    at java.time.LocalDate.parse(LocalDate.java:385)
    at chapter2.TextFileTest.readEmployee(TextFileTest.java:100)
    at chapter2.TextFileTest.readData(TextFileTest.java:76)  
    at chapter2.TextFileTest.main(TextFileTest.java:35)  
C:\Users\barcejo1\AppData\Local\NetBeans\Cache.2\executor-snippets  \run.xml:53: Java returned: 1
BUILD FAILED (total time: 21 seconds)

问题似乎出在将每行的int数字分别解析为将写入.dat文件的变量时。我复制了这段代码，但我不明白为什么它不起作用。
我期待严厉的答案，没关系。我很高兴接受教育。

import java.io.*;
import java.time.*;
import java.util.*;

/*** @version 1.14 2016-07-11
* @author Cay Horstmann
*/
public class TextFileTest
{
    public static void main(String[] args) throws IOException
    {
     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);

     // save all employee records to the file employee.dat
        try (PrintWriter out = new PrintWriter("employee.dat", "UTF-8"))
        {
        writeData(staff, out);
        }

     // retrieve all records into a new array
        try (Scanner in = new Scanner(new FileInputStream("employee.dat"), "UTF-8"))
        {
        Employee[] newStaff = readData(in);

            // print the newly read employee records
            for (Employee e : newStaff)
            System.out.println(e);
        }
    }

     //Writes all employees in an array to a print writer

    private static void writeData(Employee[] employees, PrintWriter out) throws IOException
    {
       // write number of employees
       out.println(employees.length);

       for (Employee e : employees)
       writeEmployee(out, e);
    }

     /**
     * Reads an array of employees from a scanner
     * @param in the scanner
     * @return the array of employees
     */
    private static Employee[] readData(Scanner in)
    {
       // retrieve the array size
       int n = in.nextInt();
       in.nextLine(); // consume newline

       Employee[] employees = new Employee[n];
       for (int i = 0; i < n; i++)
     {
        employees[i] = readEmployee(in);
     }
       return employees;
    }

     /**
     * Writes employee data to a print writer
     * @param out the print writer
     */
    public static void writeEmployee(PrintWriter out, Employee e)
    {
       out.println(e.getName() + "|" + e.getSalary() + "|" + e.getHireDay());
    }

     /**
     * Reads employee data from a buffered reader
     * @param in the scanner
     */
    public static Employee readEmployee(Scanner in)
    {
       String line = in.nextLine();
       String[] tokens = line.split("\|");
       String name = tokens[0];
       double salary = Double.parseDouble(tokens[1]);
       LocalDate hireDate = LocalDate.parse(tokens[2]);
       int year = hireDate.getYear();
       int month = hireDate.getMonthValue();
       int day = hireDate.getDayOfMonth();
       return new Employee(name, salary, year, month, day);
    }
}

Answer 1

您的代码无法正常工作，因为您只是在文件中写入日期。下面是固定代码：

 package com.example.demo;

import java.io.*;
import java.time.*;
import java.util.*;

/***
 * @version 1.14 2016-07-11
 * @author Cay Horstmann
 */
public class TextFileTest {
    public static void main(String[] args) throws IOException {
        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);

        // save all employee records to the file employee.dat
        try (PrintWriter out = new PrintWriter("employee.dat", "UTF-8")) {
            writeData(staff, out);
        }

        // retrieve all records into a new array
        try (Scanner in = new Scanner(new FileInputStream("employee.dat"), "UTF-8")) {
            Employee[] newStaff = readData(in);

            // print the newly read employee records
            for (Employee e : newStaff)
                System.out.println(e);
        }
    }

    //Writes all employees in an array to a print writer

    private static void writeData(Employee[] employees, PrintWriter out) throws IOException {
        // write number of employees
        out.println(employees.length);

        for (Employee e : employees)
            writeEmployee(out, e);
    }

    /**
     * Reads an array of employees from a scanner
     * 
     * @param in the scanner
     * @return the array of employees
     */
    private static Employee[] readData(Scanner in) {
        // retrieve the array size
        int n = in.nextInt();
        in.nextLine(); // consume newline

        Employee[] employees = new Employee[n];
        for (int i = 0; i < n; i++) {
            employees[i] = readEmployee(in);
        }
        return employees;
    }

    /**
     * Writes employee data to a print writer
     * 
     * @param out the print writer
     */
    public static void writeEmployee(PrintWriter out, Employee e) {
        //System.out.println(LocalDate.of(e.getYear(), e.getMonth(), e.getHireDay()).toString());
        out.println(e.getName() + "|" + e.getSalary() + "|" + LocalDate.of(e.getYear(), e.getMonth(), e.getHireDay()).toString());
    }

    /**
     * Reads employee data from a buffered reader
     * 
     * @param in the scanner
     */
    public static Employee readEmployee(Scanner in) {
        String line = in.nextLine();
        String[] tokens = line.split("\|");
        String name = tokens[0];
        double salary = Double.parseDouble(tokens[1]);
        LocalDate hireDate = LocalDate.parse(tokens[2]);
        int year = hireDate.getYear();
        int month = hireDate.getMonthValue();
        int day = hireDate.getDayOfMonth();
        return new Employee(name, salary, year, month, day);
    }
}

为什么不能正确解析我的数组元素？

Why can't the elements of my array be parsed properly?

java

datetime

parsing

inputstream

printwriter