Spring 学习总结:IOC 基础 (1),java 反射面试题及答案
package com.kevin.spring.demo2.test;
import com.kevin.spring.demo2.entity.Person;
import com.kevin.spring.demo2.entity.Student;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test {
public static void main(String[] args) {
ApplicationContext ctx = new ClassPathXmlApplicationContext("student.xml");
Person kevin = ctx.getBean("kevin", Student.class);
Person maomao = ctx.getBean("maomao", Student.class);
System.out.println(maomao);
System.out.println(kevin);
}
}
输出
信息: Loading XML bean definitions from class path resource [student.xml]
Student{height=100, name='maomao'}
Student{height=170, name='kevin'}
通过属性赋值
Animal
package com.kevin.spring.demo3.entity;
/**
动物
*/
public class Animal {
/**
动物名称
*/
private String name;
public Animal() {
}
public Animal(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Animal{" +
"name='" + name + ''' +
'}';
}
}
animal.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="dog" class="com.kevin.spring.demo3.entity.Animal">
<property name="name" value="dog"></property>
</bean>
<bean id="cat" class="com.kevin.spring.demo3.entity.Animal" p:name="cat"></bean>
</beans>
测试
package com.kevin.spring.demo3.test;
import com.kevin.spring.demo3.entity.Animal;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
/**
测试类
*/
public class Test {
public static void main(String[] args) {
ApplicationContext ctx = new ClassPathXmlApplicationContext("animal.xml");
Animal dog = ctx.getBean("dog",Animal.class);
Animal cat = ctx.getBean("cat",Animal.class);
System.out.println(cat);
System.out.println(dog);
}
}
输出结果
信息: Loading XML bean definitions from class path resource [animal.xml]
Animal{name='cat'}
Animal{name='dog'}
对象引用
Tyre
package com.kevin.spring.demo4.entity;
/**
轮胎
@author: kevin
@Date: 2018/12/8
*/
public class Tyre {
private String name;
public Tyre(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Tyre{" +
"name='" + name + ''' +
'}';
}
}
Car
package com.kevin.spring.demo4.entity;
/**
车
*/
public class Car {
private String name;
private Tyre tyre;
public Car(String name, Tyre tyre) {
this.name = name;
this.tyre = tyre;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Tyre getTyre() {
return tyre;
}
public void setTyre(Tyre tyre) {
this.tyre = tyre;
}
@Override
public String toString() {
return "Car{" +
"name='" + name + ''' +
", tyre=" + tyre +
'}';
}
}
测试
package com.kevin.spring.demo4.test;
import com.kevin.spring.demo4.entity.Car;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Test {
public static void main(String[] args) {
ApplicationContext ctx = new ClassPathXmlApplicationContext("car.xml");
Car bike = ctx.getBean("bike", Car.class);
System.out.println(bike);
}
}
输出结果
信息: Loading XML bean definitions from class path resource [car.xml]
Car{name='bike', tyre=Tyre{name='自行车轮胎'}}
对象作用域
在大多数情况下,单例 bean 是很理想的方案。初始化和垃圾回收对象实例所带来的的成本只留给一些小规模任务,在这些任务中,让对象保持无状态并且在应用中反复重用这些对象可能并不合理。在这种情况下,将 class 声明为单例的 bean 会被污染,稍后重用的时候会出现意想不到的问题。 -《spring 实战》
Spring 定义了多种作用域,可以基于这些作用域创建 bean,包括:
| 作用域 | 描述 |
| --- | --- |
| 单例(Singleton) | 在整个应用中,只创建 bean 的一个实例 |
| 原型(Prototype) | 每次注入或者通过 spring 应用上下文获取的时候,都会创建一个新的 bean 实例 |
| 会话(Session) | 在 web 应用中,为每个会话创建一个 bean 实例 |
| 请求(Request) | 在 web 应用中,为每个请求创建一个 bean 实例 |
1、spring 中默认是单例的,我们通过之前的代码演示下
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="dog" class="com.kevin.spring.demo3.entity.Animal">
<property name="name" value="dog"></property>
</bean>
<bean id="cat" class="com.kevin.spring.demo3.entity.Animal" p:name="cat"></bean>
</beans>
测试
package com.kevin.spring.demo3.test;
import com.kevin.spring.demo3.entity.Animal;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
/**
测试类
*/
public class Test {
public static void main(String[] args) {
ApplicationContext ctx = new ClassPathXmlApplicationContext("animal.xml");
Animal dog1 = ctx.getBean("dog",Animal.class);
Animal dog2 = ctx.getBean("dog",Animal.class);
System.out.println(dog1 == dog2);
}
}
输出结果
true
这样验证了从容器中取回的对象默认是单例的。
2、设置成 Prototype
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="dog" class="com.kevin.spring.demo3.entity.Animal" scope="prototype">
<property name="name" value="dog"></property>
</bean>
<bean id="cat" class="com.kevin.spring.demo3.entity.Animal" p:name="cat"></bean>
</beans>
测试
ApplicationContext ctx = new ClassPathXmlApplicationContext("animal.xml");
Animal dog1 = ctx.getBean("dog",Animal.class);
Animal dog2 = ctx.getBean("dog",Animal.class);
System.out.println(dog1 == dog2);
输出结果
false
延迟初始化 bean
ApplicationContext 实现的默认行为是在启动时将所有的 singleton bean 提前进行实例化。这样配置中或者运行环境的错误就会立刻发现。如果你想延迟初始化。可以在 xml 中进行配置
<bean id="kevin" class="com.kevin.spring.demo2.entity.Student" lazy-init="true">
<constructor-arg name="name" value="kevin"></constructor-arg>
<constructor-arg name="height" value="170"></constructor-arg>
</bean>
测试
public static void main(String[] args) throws InterruptedException {
ApplicationContext ctx = new ClassPathXmlApplicationContext("student.xml");
Thread.sleep(3000);
Person kevin = ctx.getBean("kevin", Student.class);
System.out.println(kevin);
}
大家自己运行后发现,确实并不是启动后就加载的。
回调方法
Student
public void init() {
System.out.println("执行 init 方法");
}
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