用非常硬核的JAVA序列化手段实现对象流的持久化保存
奔跑的男人 · 337浏览 · 发布于2020-05-28
背景
在OOP（面向对象编程）中处处是对象，我们当然希望可以有一种数据格式来存储这种对象的集合，以实现持久化。比如部门类所形成的部门对象集合，员工类所形成的员工对象集合，甚至是这样一个类所形成的对象：公司中有多个部门，每个部门有多个员工，我们希望将这样一个对象以文件的方式实现持久化保存。
对象流的概念
为实现对象的持久化保存，我们需要引入Java语言的对象序列化（object serialization）机制，这种机制可以将任何对象输出到流中：比如
/**
*流对象
*/Object object = new Object();//创建对象流并输出到文件object.datObjectOutputStream output = new ObjectOutputStream(new FileOutputStream("c:\\object.dat"));//将object对象写到文件中output.writeObject(object);
ObjectInputStream input = new ObjectInputStream(new FileInputStream("c:\\object.dat"));
object = input.readObject();对象流实例
引入一张组织结构图
定义组织架构图的类
公司：代表了组织架构的外在存在；公司是由部门和职员组成的一个完整实体。
部门：代表了组织架构中的运作单位；部门按类型不同可以分为不同的业务部门。
职员：代表了组织架构中的最小单位；职员按职位不同存在于不同的业务部门。
/**
* 用对象流保存信息--公司类
*
* @author zhuhuix
* @date 2020-05-27
*/
class Company implements Serializable { //公司id
private int id; //公司名称
private String name; //公司部门列表
private List<Department> departments; //默认构造函数
Company() {
} //初始化构造函数
Company(int id, String name) { this.id = id; this.name = name; this.departments = new ArrayList<>();
} //增加部门
public void addDepartment(Department department) { this.departments.add(department);
} //裁撤部门
public void deleteDepartment(Department department) { this.departments.remove(department);
} //定位部门
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;
}
}/**
* 用对象流保存信息--部门类
*
* @author zhuhuix
* @date 2020-05-27
*/
class Department implements Serializable { //部门id
private int id; //部门名称
private String name; //上级部门
private Integer parentId; //部门职员列表
private List<Employee> employees; //默认构造函数
Department(){} //初始化构造函数
Department(int id,String name,Integer parentId){ this.id=id; this.name=name; this.parentId=parentId; this.employees = new ArrayList<>();
} //增加职员
public void addEmployee(Employee employee){ this.employees.add(employee);
} //裁撤职员
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;
}
}/**
* 用对象流保存信息--职员类
*
* @author zhuhuix
* @date 2020-05-27
*/
class Employee implements Serializable { //职员id
private int id; //职员姓名
private String name; //职员性别
private String sex; //职员年龄
private int age; //职员职位
private String position; //入职日期
private Date hireDate; //当前薪水
private BigDecimal salary; //默认构造函数
Employee(){} //初始化构造函数
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;
} //升职、调岗、调动
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;
}
}类的完整结构
用对象流保存组织架构的对象信息
有了类及构造函数完成对象的初始化过程，我们就具备了建立整个组织架构的能力，接下来我们完整地建立一个公司的组织架构：
/**
1. 用对象流保存组织架构信息
2. * @author zhuhuix
3. @date 2020-05-27
*/public class ObjectStreamSave { //定义一个全局静态变量，作为控制组织架构的id
public static int id = 0; public static void main(String[] args) throws IOException { //设立公司
Company company = new Company(id++, "互联网股份有限公司"); //公司设立总经理室
Department manageDept = new Department(id++, "总经理室", null);
company.addDepartment(manageDept); //在总经理室下设立产品部
Department productDept = new Department(id++, "产品部", manageDept.getId());
company.addDepartment(productDept); //在产品部下设立产品A、B组
company.addDepartment(new Department(id++, "产品A组", productDept.getId()));
company.addDepartment(new Department(id++, "产品B组", productDept.getId())); //在总经理室下设立研发部
Department developmentDept = new Department(id++, "研发部", manageDept.getId());
company.addDepartment(developmentDept); //在研发部下设立软件组与硬件组
company.addDepartment(new Department(id++, "软件组", developmentDept.getId()));
company.addDepartment(new Department(id++, "硬件组", developmentDept.getId())); //在总经理室下设立市场部
Department marketDept = new Department(id++, "市场部", manageDept.getId());
company.addDepartment(marketDept); //在市场部下设立创意组与渠道组
company.addDepartment(new Department(id++, "创意组", marketDept.getId()));
company.addDepartment(new Department(id++, "渠道组", marketDept.getId())); //总经理室人事任命
manageDept.addEmployee(new Employee(id++, "Mike", "男", 35, "总经理", new Date(), BigDecimal.valueOf(100000)));
manageDept.addEmployee(new Employee(id++, "Tom", "男", 34, "副总经理", new Date(), BigDecimal.valueOf(60000))); //研发部人事任命
developmentDept.addEmployee(new Employee(id++, "Jack", "男", 30, "研发部主管", new Date(), BigDecimal.valueOf(40000)));
company.findDepartmentByName("软件组")
.addEmployee(new Employee(id++, "Kate", "女", 26, "组员", new Date(), BigDecimal.valueOf(20000)));
company.findDepartmentByName("硬件组")
.addEmployee(new Employee(id++, "Will", "男", 24, "组员", new Date(), BigDecimal.valueOf(20000))); //产品部人事任命
productDept.addEmployee(new Employee(id++, "Jerry", "男", 28, "产品部主管", new Date(), BigDecimal.valueOf(40000)));
company.findDepartmentByName("产品A组")
.addEmployee(new Employee(id++, "Merry", "女", 28, "组员", new Date(), BigDecimal.valueOf(20000)));
company.findDepartmentByName("产品B组")
.addEmployee(new Employee(id++, "Leo", "男", 27, "组员", new Date(), BigDecimal.valueOf(20000))); //市场部人事任命
marketDept.addEmployee(new Employee(id++, "Rose", "女", 29, "市场部主管", new Date(), BigDecimal.valueOf(40000)));
company.findDepartmentByName("创意组")
.addEmployee(new Employee(id++, "Amy", "", 25, "组员", new Date(), BigDecimal.valueOf(20000)));
company.findDepartmentByName("渠道组")
.addEmployee(new Employee(id++, "Tony", "男", 23, "组员", new Date(), BigDecimal.valueOf(20000))); //遍历公司组织结构
int deptCount = 0; int empCount = 0;
Iterator<Department> deptIterator = company.getDepartments().iterator(); while (deptIterator.hasNext()) {
deptCount++;
Department department = deptIterator.next();
System.out.println("部门:" + department.getName()); if (department.getEmployees() != null) {
Iterator<Employee> empIterator = department.getEmployees().iterator(); while (empIterator.hasNext()) {
empCount++;
Employee employee = empIterator.next();
System.out.print(" 人员:" + employee.getName() + " 职位:" + employee.getPosition() + ",");
}
System.out.println();
}
}
System.out.println("总共部门数：" + deptCount);
System.out.println("总共职员数：" + empCount); //通过对象流将公司组织架构保存到文件中
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);
}
}
}核心代码
通过对象流的方式建立一个company.dat文件
将公司对象写入文件
将公司对象中的部门列表集合写入文件
遍历部门列表，将每个部门下的职员列表集合写入文件
生成的文件如下：
二进制信息：
用对象流读取文件并输出
/**
* 用对象流读取信息
*
* @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(); //遍历公司组织结构
int deptCount = 0; int empCount = 0;
Iterator<Department> deptIterator = company.getDepartments().iterator(); while (deptIterator.hasNext()) {
deptCount++;
Department department = deptIterator.next();
System.out.println("部门:" + department.getName()); if (department.getEmployees() != null) {
Iterator<Employee> empIterator = department.getEmployees().iterator(); while (empIterator.hasNext()) {
empCount++;
Employee employee = empIterator.next();
System.out.print(" 人员:" + employee.getName() + " 职位:" + employee.getPosition() + ",");
}
System.out.println();
}
}
System.out.println("总共部门数：" + deptCount);
System.out.println("总共职员数：" + empCount);
}
}
}核心代码
通过对象流的方式获取company.dat文件
读取对象信息
输出如下：
总结
在本文中，我们使用序列化将对象集合保存到磁盘文件中，并按照它们被存储的样子获取它们，我们学习到了如下信息：
ObjectOutputStream（OutputStream out） 创建一个ObjectOutputStream使得你可以将对象写出到指定的OutputStream。
void writeObject（Object obj） 写出指定的对象到ObjectOutputStream，这个方法将存储指定对象的类、类的签名以及这个类及其超类中所有非静态和非瞬时的域的值。
ObjectInputStream（InputStream in） 创建一个ObjectInputStream用于从指定的InputStream中读回对象信息。
Object readObject（）从ObjectInputStream中读入一个对象。特别是，这个方法会读回对象的类、类的签名以及这个类及其超类中所有非静态和非瞬时的域的值。它执行的反序列化允许恢复多个对象引用。
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