背景
在OOP（物件導向程式設計）中處處是物件，我們當然希望可以有一種資料格式來儲存這種物件的集合，以實現持久化。比如部門類所形成的部門物件集合，員工類所形成的員工物件集合，甚至是這樣一個類所形成的物件：公司中有多個部門，每個部門有多個員工，我們希望將這樣一個物件以檔案的方式實現持久化儲存。
物件流的概念
為實現物件的持久化儲存，我們需要引入Java語言的物件序列化（object serialization）機制，這種機制可以將任何物件輸出到流中：比如
/**
*流物件
*/
Object object = new Object();
//建立物件流並輸出到檔案object.dat
ObjectOutputStream output = new ObjectOutputStream(new FileOutputStream("c:\\object.dat"));
//將object物件寫到檔案中
output.writeObject(object);
ObjectInputStream input = new ObjectInputStream(new FileInputStream("c:\\object.dat"));
object = input.readObject();
物件流例項
引入一張組織結構圖
定義組織架構圖的類
- 公司：代表了組織架構的外在存在；公司是由部門和職員組成的一個完整實體。
- 部門：代表了組織架構中的運作單位；部門按型別不同可以分為不同的業務部門。
- 職員：代表了組織架構中的最小單位；職員按職位不同存在於不同的業務部門。
/**
* 用物件流儲存資訊--公司類
*
* @author zhuhuix
* @date 2020-05-27
*/
class Company implements Serializable {
//公司id
private int id;
//公司名稱
private String name;
//公司部門列表
private List<Department> departments;
//預設建構函式
Company() {
}
//初始化建構函式
Company(int id, String name) {
this.id = id;
this.name = name;
this.departments = new ArrayList<>();
}
//增加部門
public void addDepartment(Department department) {
this.departments.add(department);
}
//裁撤部門
public void deleteDepartment(Department department) {
this.departments.remove(department);
}
//定位部門
Department findDepartmentByName(String departmentName) {
Optional<Department> optional = departments.stream().filter(department ->
department.getName().equals(departmentName)).findFirst();
return optional.get();
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<Department> getDepartments() {
return departments;
}
public void setDepartments(List<Department> departments) {
this.departments = departments;
}
}
/**
* 用物件流儲存資訊--部門類
*
* @author zhuhuix
* @date 2020-05-27
*/
class Department implements Serializable {
//部門id
private int id;
//部門名稱
private String name;
//上級部門
private Integer parentId;
//部門職員列表
private List<Employee> employees;
//預設建構函式
Department(){}
//初始化建構函式
Department(int id,String name,Integer parentId){
this.id=id;
this.name=name;
this.parentId=parentId;
this.employees = new ArrayList<>();
}
//增加職員
public void addEmployee(Employee employee){
this.employees.add(employee);
}
//裁撤職員
public void deleteEmployee(Employee employee){
this.employees.remove(employee);
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getParentId() {
return parentId;
}
public void setParentId(Integer parentId) {
this.parentId = parentId;
}
public List<Employee> getEmployees() {
return employees;
}
public void setEmployees(List<Employee> employees) {
this.employees = employees;
}
}
/**
* 用物件流儲存資訊--職員類
*
* @author zhuhuix
* @date 2020-05-27
*/
class Employee implements Serializable {
//職員id
private int id;
//職員姓名
private String name;
//職員性別
private String sex;
//職員年齡
private int age;
//職員職位
private String position;
//入職日期
private Date hireDate;
//當前薪水
private BigDecimal salary;
//預設建構函式
Employee(){}
//初始化建構函式
public Employee(int id, String name, String sex, int age, String position, Date hireDate, BigDecimal salary) {
this.id = id;
this.name = name;
this.sex = sex;
this.age = age;
this.position = position;
this.hireDate = hireDate;
this.salary = salary;
}
//升職、調崗、調動
public void setPosition(String position){
this.position = position;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getPosition() {
return position;
}
public Date getHireDate() {
return hireDate;
}
public void setHireDate(Date hireDate) {
this.hireDate = hireDate;
}
public BigDecimal getSalary() {
return salary;
}
public void setSalary(BigDecimal salary) {
this.salary = salary;
}
}
類的完整結構
用物件流儲存組織架構的物件資訊
有了類及建構函式完成物件的初始化過程，我們就具備了建立整個組織架構的能力，接下來我們完整地建立一個公司的組織架構：
/**
1. 用物件流儲存組織架構資訊
2. * @author zhuhuix
3. @date 2020-05-27
*/
public class ObjectStreamSave {
//定義一個全域性靜態變數，作為控制組織架構的id
public static int id = 0;
public static void main(String[] args) throws IOException {
//設立公司
Company company = new Company(id++, "網際網路股份有限公司");
//公司設立總經理室
Department manageDept = new Department(id++, "總經理室", null);
company.addDepartment(manageDept);
//在總經理室下設立產品部
Department productDept = new Department(id++, "產品部", manageDept.getId());
company.addDepartment(productDept);
//在產品部下設立產品A、B組
company.addDepartment(new Department(id++, "產品A組", productDept.getId()));
company.addDepartment(new Department(id++, "產品B組", productDept.getId()));
//在總經理室下設立研發部
Department developmentDept = new Department(id++, "研發部", manageDept.getId());
company.addDepartment(developmentDept);
//在研發部下設立軟體組與硬體組
company.addDepartment(new Department(id++, "軟體組", developmentDept.getId()));
company.addDepartment(new Department(id++, "硬體組", developmentDept.getId()));
//在總經理室下設立市場部
Department marketDept = new Department(id++, "市場部", manageDept.getId());
company.addDepartment(marketDept);
//在市場部下設立創意組與渠道組
company.addDepartment(new Department(id++, "創意組", marketDept.getId()));
company.addDepartment(new Department(id++, "渠道組", marketDept.getId()));
//總經理室人事任命
manageDept.addEmployee(new Employee(id++, "Mike", "男", 35, "總經理",
new Date(), BigDecimal.valueOf(100000)));
manageDept.addEmployee(new Employee(id++, "Tom", "男", 34, "副總經理",
new Date(), BigDecimal.valueOf(60000)));
//研發部人事任命
developmentDept.addEmployee(new Employee(id++, "Jack", "男", 30, "研發部主管",
new Date(), BigDecimal.valueOf(40000)));
company.findDepartmentByName("軟體組")
.addEmployee(new Employee(id++, "Kate", "女", 26, "組員",
new Date(), BigDecimal.valueOf(20000)));
company.findDepartmentByName("硬體組")
.addEmployee(new Employee(id++, "Will", "男", 24, "組員",
new Date(), BigDecimal.valueOf(20000)));
//產品部人事任命
productDept.addEmployee(new Employee(id++, "Jerry", "男", 28, "產品部主管",
new Date(), BigDecimal.valueOf(40000)));
company.findDepartmentByName("產品A組")
.addEmployee(new Employee(id++, "Merry", "女", 28, "組員",
new Date(), BigDecimal.valueOf(20000)));
company.findDepartmentByName("產品B組")
.addEmployee(new Employee(id++, "Leo", "男", 27, "組員",
new Date(), BigDecimal.valueOf(20000)));
//市場部人事任命
marketDept.addEmployee(new Employee(id++, "Rose", "女", 29, "市場部主管",
new Date(), BigDecimal.valueOf(40000)));
company.findDepartmentByName("創意組")
.addEmployee(new Employee(id++, "Amy", "", 25, "組員",
new Date(), BigDecimal.valueOf(20000)));
company.findDepartmentByName("渠道組")
.addEmployee(new Employee(id++, "Tony", "男", 23, "組員",
new Date(), BigDecimal.valueOf(20000)));
//遍歷公司組織結構
int deptCount = 0;
int empCount = 0;
Iterator<Department> deptIterator = company.getDepartments().iterator();
while (deptIterator.hasNext()) {
deptCount++;
Department department = deptIterator.next();
System.out.println("部門:" + department.getName());
if (department.getEmployees() != null) {
Iterator<Employee> empIterator = department.getEmployees().iterator();
while (empIterator.hasNext()) {
empCount++;
Employee employee = empIterator.next();
System.out.print(" 人員:" + employee.getName() + " 職位:" + employee.getPosition() + ",");
}
System.out.println();
}
}
System.out.println("總共部門數：" + deptCount);
System.out.println("總共職員數：" + empCount);
//通過物件流將公司組織架構儲存到檔案中
ObjectOutputStream companyStream = new ObjectOutputStream(new FileOutputStream("c:\\company.dat"));
companyStream.writeObject(company);
companyStream.writeObject(company.getDepartments());
for (int i = 0; i < company.getDepartments().size(); i++) {
List<Employee> employees = company.getDepartments().get(i).getEmployees();
companyStream.writeObject(employees);
}
}
}
核心程式碼
- 通過物件流的方式建立一個company.dat檔案
- 將公司物件寫入檔案
- 將公司物件中的部門列表集合寫入檔案
- 遍歷部門列表，將每個部門下的職員列表集合寫入檔案
生成的檔案如下：
二進位制資訊：
用物件流讀取檔案並輸出
/**
* 用物件流讀取資訊
*
* @author zhuhuix
* @date 2020-05-27
*/
public class ObjectStreamRead {
public static void main(String[] args) throws IOException, ClassNotFoundException {
ObjectInputStream companyStream = new ObjectInputStream(new FileInputStream("c:\\company.dat"));
if (companyStream!=null){
Company company=(Company) companyStream.readObject();
//遍歷公司組織結構
int deptCount = 0;
int empCount = 0;
Iterator<Department> deptIterator = company.getDepartments().iterator();
while (deptIterator.hasNext()) {
deptCount++;
Department department = deptIterator.next();
System.out.println("部門:" + department.getName());
if (department.getEmployees() != null) {
Iterator<Employee> empIterator = department.getEmployees().iterator();
while (empIterator.hasNext()) {
empCount++;
Employee employee = empIterator.next();
System.out.print(" 人員:" + employee.getName() + " 職位:" + employee.getPosition() + ",");
}
System.out.println();
}
}
System.out.println("總共部門數：" + deptCount);
System.out.println("總共職員數：" + empCount);
}
}
}
核心程式碼
- 通過物件流的方式獲取company.dat檔案
- 讀取物件資訊
輸出如下：
總結
在本文中，我們使用序列化將物件集合儲存到磁碟檔案中，並按照它們被儲存的樣子獲取它們，我們學習到了如下資訊：
- ObjectOutputStream（OutputStream out） 建立一個ObjectOutputStream使得你可以將物件寫出到指定的OutputStream。
- void writeObject（Object obj） 寫出指定的物件到ObjectOutputStream，這個方法將儲存指定物件的類、類的簽名以及這個類及其超類中所有非靜態和非瞬時的域的值。
- ObjectInputStream（InputStream in） 建立一個ObjectInputStream用於從指定的InputStream中讀回物件資訊。
- Object readObject（）從ObjectInputStream中讀入一個物件。特別是，這個方法會讀回物件的類、類的簽名以及這個類及其超類中所有非靜態和非瞬時的域的值。它執行的反序列化允許恢復多個物件引用。