import java.io.*;
import java.time.LocalDate;

public class Test {
    public static void main(String[] args){
        RandomAccessTest.test();
    }
}

/*
    2.3 讀寫二進制數據
 */


/*
    2.3.2 隨機訪問文件
    寫了大半天，突然發現這個實驗好像不是太嚴謹：
        1.RandomAccessFile算長度時，應該是根據字節數算出來的
        2.寫字符串時，我們只是指定了碼元數量，我們寫的是固定碼元數量的字符串
        3.這樣的化，我們記錄的Employee.RECORD_SIZE根本就代表不了一條記錄的長度
        4.但是我們最後又通過RandomAccessFile的長度和Employee.RECORD_SIZE來計算記錄數量
        5.我覺得這個實驗有問題，以後研究吧
 
 
*/

class Employee {
    private String name;
    private double salary;
    private LocalDate hireDay;
    public static final int NAME_SIZE = 30;
    public static final int RECORD_SIZE = 50;

    public Employee(String name, double salary, LocalDate hireDay) {
        this.name = name;
        
 
this.salary = salary;
        this.hireDay = hireDay;
    }

    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 LocalDate getHireDay() {
        return hireDay;
    }

    public void setHireDay(LocalDate hireDay) {
        this.hireDay = hireDay;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "name=‘" + name + ‘\‘‘ +
                ", salary=" + salary +
                ", hireDay=" + hireDay +
                ‘}‘;
    }
}

class DataIO {
    //Java核心技術 卷二 第十版 2.3.2節
    //寫出從字符串開頭開始的指定數量的碼元，如果碼元過少，該方法會用‘0’來補齊字符串
    public static void writeFixedString(String s, int size, DataOutput output) throws IOException {
        for (int i = 0; i < size; i++) {
            char ch =0;
            if(i<s.length())
                ch = s.charAt(i);
            output.write(ch);
        }
    }

    //Java核心技術 卷二 第十版 2.3.2節
    //從輸入流中讀入字符，直至讀入size個碼元，或者直至遇到具有0值的字符串，然後跳出輸入字段中剩余的0值。
    public static String readFixedString1(int size, DataInput in) throws IOException {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < size; i++) {
            char c;
            if ((c = in.readChar()) != 0) {
                sb.append(c);
            }
        }
        return sb.toString();
    }

    //功能和上一個方法是一樣的，但是這個效率會高那麽一點點
    public static String readFixedString2(int size, DataInput in) throws IOException {
        StringBuilder sb = new StringBuilder();
        /*
        int i;
        for (i = 0; i < size; i++) {
            char c;
            if ((c = in.readChar()) == 0) {
                break;
            }
            sb.append(c);
        }
        in.skipBytes(2*(size-i));   //這個地方不是太嚴謹
        */

        //用書中代碼測試一下
        int i =0;
        boolean more = true;
        while (more && i < size) {
            char ch = in.readChar();
            i++;
            if (ch == 0) {
                more = false;
            } else {
                sb.append(ch);
            }
        }
        in.skipBytes(2 * (size - i));


        return sb.toString();
    }
}

class RandomAccessTest {
    public static void test() {
        Employee[] staff = new Employee[]{
                new Employee("A", 10, LocalDate.now()),
                new Employee("B", 20, LocalDate.now()),
                new Employee("C", 30, LocalDate.now())
        };

        //寫入
        try(DataOutputStream out = new DataOutputStream(new FileOutputStream("employee1.dat"))) {

            for (Employee e : staff) {
                writeData(out, e);
            }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

        //讀取

        try(RandomAccessFile in = new RandomAccessFile("employee1.dat","r")) {
            int n = (int) (in.length() / Employee.RECORD_SIZE);
            Employee[] newStaff = new Employee[n];

            for (int i = n - 1; i >= 0; i--) {
                in.seek(i*Employee.RECORD_SIZE);
                newStaff[i] = readDate(in);
            }

            for (Employee e : newStaff) {
                System.out.println(e);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }





    }

    private static void writeData(DataOutput out, Employee employee) throws IOException {
        DataIO.writeFixedString(employee.getName(), Employee.NAME_SIZE, out);
        out.writeDouble(employee.getSalary());

        LocalDate hireDay = employee.getHireDay();
        out.writeInt(hireDay.getYear());
        out.writeInt(hireDay.getMonthValue());
        out.writeInt(hireDay.getDayOfMonth());
    }

    private static Employee readDate(DataInput input) throws IOException {
        String name = DataIO.readFixedString2(Employee.NAME_SIZE, input);
        double salary = input.readDouble();
        int
                y= input.readInt(),
                m= input.readInt(),
                d= input.readInt();
        return new Employee(name, salary, LocalDate.of(y, m, d));
    }
}

/*
    2.3.3 ZIP文檔

    ZipFile API：
        ZipFile(String name)
        ZipFile(File file)
        Enumeration entries()
        ZipEntry getEntry(String name)
        InputStream getInputStream(ZipEntry ze)
        String getName()
        
    從這個類的API中可以看出來，還有一種使用Zip的方案。先通過ZipFile對象，得到
    這個壓縮包中的每一條記錄，然後再指定某條具體的記錄，得到其中的數據。
 */

《Java核心技術卷二》筆記

Java讀寫二進制數據