关于FactoryBean的个人理解

有基本学生类结构：

package top.dreamcenter.test.bean;
 
import java.text.SimpleDateFormat;
import java.util.Calendar;
 
public class Student {
    private int age;
    private Calendar birth;
     
    public Student() {}
    public Student(int age, Calendar birth) {
    super();
        this.age = age;
        this.birth = birth;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Calendar getBirth() {
        return birth;
    }
    public void setBirth(Calendar birth) {
        this.birth = birth;
    }
     
    private String shortBirthString() {
        if (birth == null) return "NULL";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        return sdf.format(birth.getTime());
    }
     
    @Override
    public String toString() {
        return getClass().getSimpleName()
            + ":{
	age:" + age + ",
	birth:"" + shortBirthString() + ""
}";
    }
}

基本方式创建类对象并初始化：

package top.dreamcenter.test.core;
 
import java.util.Calendar;
 
import top.dreamcenter.test.bean.Student;
 
public class Core {
    public static void main(String[] args) {
        Calendar now = Calendar.getInstance();
        int age = 0;
         
        Calendar temp1 = Calendar.getInstance();
        temp1.set(2000, 12 - 1, 12);
        age  = now.get(Calendar.YEAR)-temp1.get(Calendar.YEAR);
        Student zhangSan = new Student(age, temp1);
         
        Calendar temp2 = Calendar.getInstance();
        temp2.set(2001, 3 - 1, 5);
        age  = now.get(Calendar.YEAR)-temp2.get(Calendar.YEAR);
        Student liSi = new Student(age,temp2);
         
        System.out.println(zhangSan);
        System.out.println(liSi);
    }
}

问题发现1：对象的初始化于主体中过于过于复杂

解决措施1：将对象的创建与初始化在对象自己内部暴露出来

public static Student getStudent(int year, int month, int date) {
    Calendar now = Calendar.getInstance();
    Calendar temp = Calendar.getInstance();
    temp.set(year, month - 1, date);
    int age  = now.get(Calendar.YEAR)-temp.get(Calendar.YEAR);
    Student student = new Student(age, temp);
    return student;
}

 

此时，main函数只要简短的两句即可创建:

 

Student zhangSan = Student.getStudent(2000, 12, 12);
Student liSi = Student.getStudent(2001, 3, 5);

问题发现2：如果在初始化时要求添加多个监听器，假如用解决措施1将会导致bean类实现了过多的接口

解决措施2：使用FactoryBean模式创建对象

// 基本学生类结构：

package top.dreamcenter.test.bean;
 
import java.text.SimpleDateFormat;
import java.util.Calendar;
 
public class Student implements Cloneable{
    private int age;
    private Calendar birth;
    private String name;
     
    public Student() {}
    public Student(String name, int age, Calendar birth) {
        this.age = age;
        this.birth = birth;
        this.name = name;
    }
     
    protected String getName() {
        return name;
    }
     
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Calendar getBirth() {
        return birth;
    }
    public void setBirth(Calendar birth) {
        this.birth = birth;
    }
     
    public String shortBirthString() {
        if (birth == null) return "NULL";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        return sdf.format(birth.getTime());
    }
     
    @Override
    protected Object clone() throws CloneNotSupportedException {
        Student student = (Student)super.clone();
        student.birth = (Calendar)birth.clone();
        return student;
    }
    @Override
    public String toString() {
        return name + ":{
	age:" + age + ",
	birth:"" + shortBirthString() + ""
}";
    }
}

// 简易的信息改变监听器

package top.dreamcenter.test.core;
 
public interface InfoListener {
    void onInfoChanged();
    void closeListener();
}

// 工厂类创建

package top.dreamcenter.test.bean;
 
import java.util.Calendar;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
 
import top.dreamcenter.test.core.InfoListener;
 
public class StudentFactoryBean implements InfoListener{
    private Student tempStudent;
    private Set<MyThread> set;
    private boolean isNotCheck;
     
    public StudentFactoryBean() {
        set = new HashSet<MyThread>();
    }
     
    public Student getStudent(String name, int year, int month, int date) {
        Calendar now = Calendar.getInstance();
        Calendar temp = Calendar.getInstance();
        temp.set(year, month - 1, date);
        int age  = now.get(Calendar.YEAR)-temp.get(Calendar.YEAR);
         
        tempStudent = new Student(name, age, temp);
        onInfoChanged();
        return tempStudent;
    }
     
    private class MyThread extends Thread{
        private Student myStudent;
        private boolean check;
        public MyThread() {
            check = !isNotCheck;
            myStudent = tempStudent;
        }
        public void run() {
            try {
                Student before = (Student) myStudent.clone();
                while(check) {
                    sleep(100);
                    if (myStudent.getAge()!=before.getAge()
                        ||!myStudent.shortBirthString().equals(before.shortBirthString())) {
                        System.err.println(myStudent.getName() + " info changed!");
                        before = (Student) myStudent.clone();
                    }
                }
            } catch (CloneNotSupportedException e) {
                e.printStackTrace();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
     
    @Override
    public void onInfoChanged() {
        MyThread myThread = new MyThread();
        myThread.start();
        set.add(myThread);
    }
     
    @Override
    public void closeListener() {
        isNotCheck = false;
        Iterator<MyThread> iterator = set.iterator();
        while(iterator.hasNext()) {
            iterator.next().check = false;
        }
    }
}

// 测试示例

package top.dreamcenter.test.core;
 
import java.util.Calendar;
import java.util.Scanner;
 
import top.dreamcenter.test.bean.Student;
import top.dreamcenter.test.bean.StudentFactoryBean;
 
public class Core {
private static StudentFactoryBean sfb;
    public static void main(String[] args) {
        sfb = new StudentFactoryBean();
         
        Student zhangSan = sfb.getStudent("Zhang_San", 2000, 12, 12);
        Student liSi = sfb.getStudent("Li_Si", 2001, 3, 5);

                        // 此时学生类都已经初始化好并且添加了信息变动监听器
         
        System.out.println("set age :");
        while(true) {
            Scanner scanner = new Scanner(System.in);
            int age = scanner.nextInt();
            if (age == 0) break;
            else if (age < 0) zhangSan.setAge(-age);
            else liSi.setAge(age);
        }
         
        sfb.closeListener();
        System.out.println(zhangSan);
        System.out.println(liSi);
    }
}

 

所以FactoryBean出现的目的是让复杂的初始化问题简化，

并且让Bean本身更加的短小精悍，

同时降低了Bean本身对其它类或者接口的依赖性。

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