用非常硬核的JAVA序列化手段实现对象流的持久化保存

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.dat
ObjectOutputStream 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。