Spring框架第三篇之基于XML的DI注入
一、注入分类
Bean实例在调用无参构造器创建空值对象后，就要对Bean对象的属性进行初始化。初始化是由容器自动完成的，称为注入。根据注入方式的不同，常用的有两类：设值注入、构造注入、实现特定接口注入。由于第三种方式采用侵入式编程，污染代码，所以几乎不用。
1、设值注入
设值注入是指，通过setter方法传入被调用者的实例。这种注入方式简单、直观，因而在Spring的依赖注入中大量使用。
关于设值注入举个简单的例子：
分别创建一个学校类（School）：
/**
* 学校类
*
* @author Root
*/
public class School { private String name; public void setName(String name) {
this.name = name;
} @Override
public String toString() {
return "School [name=" + name + "]";
} }
学生类（Student）：
/**
* 学生类
*
* @author Root
*/
public class Student { private String name;
private int age;
// 对象属性，也叫做域属性
private School school; public Student() {
super();
} public void setName(String name) {
System.out.println("执行setName()");
this.name = name;
} public void setAge(int age) {
System.out.println("执行setAge()");
this.age = age;
} public void setSchool(School school) {
this.school = school;
} @Override
public String toString() {
return "Student [name=" + name + ", age=" + age + ", school=" + school + "]";
} }
在配置文件中使用设值注入方式，设值对象属性值：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- 注册School -->
<bean id="school" class="com.ietree.spring.basic.di.setter.School">
<property name="name" value="北京大学"></property>
</bean> <!-- 注册Student -->
<bean id="student" class="com.ietree.spring.basic.di.setter.Student">
<property name="name" value="李华"></property>
<property name="age" value="20"></property>
<!-- 域属性注入使用ref -->
<property name="school" ref="school"></property>
</bean> </beans>
注意：如果对象中包含有另外的对象引用，则需要使用ref，而不能使用value。
测试：
@Test
public void test01(){ String resource = "com/ietree/spring/basic/di/setter/applicationContext.xml";
ApplicationContext ctx = new ClassPathXmlApplicationContext(resource); Student student = (Student) ctx.getBean("student");
System.out.println(student);
}
程序输出：
执行setName()
执行setAge()
Student [name=李华, age=20, school=School [name=北京大学]]
2、构造注入
构造注入，顾名思义就是通过构造方法注入，举个简单的例子：
创建一个学校类（School）：
/**
* 学校类
*
* @author Root
*/
public class School { private String name; public void setName(String name) {
this.name = name;
} @Override
public String toString() {
return "School [name=" + name + "]";
} }
学生类（Student）：
/**
* 学生类
*
* @author Root
*/
public class Student { private String name;
private int age;
// 对象属性，也叫做域属性
private School school; /*public Student() {
super();
}*/ // 代参构造器
public Student(String name, int age, School school) {
super();
this.name = name;
this.age = age;
this.school = school;
} public void setName(String name) {
System.out.println("执行setName()");
this.name = name;
} public void setAge(int age) {
System.out.println("执行setAge()");
this.age = age;
} public void setSchool(School school) {
this.school = school;
} @Override
public String toString() {
return "Student [name=" + name + ", age=" + age + ", school=" + school + "]";
} }
配置文件：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- 注册School -->
<bean id="school" class="com.ietree.spring.basic.di.constructor.School">
<property name="name" value="北京大学"></property>
</bean> <!-- 注册Student -->
<!-- 方式一 -->
<!-- <bean id="student" class="com.ietree.spring.basic.di.constructor.Student">
<constructor-arg index="0" value="李华"/>
<constructor-arg index="1" value="20"/>
<constructor-arg index="2" ref="school"/>
</bean> --> <!-- 方式二 -->
<!-- <bean id="student" class="com.ietree.spring.basic.di.constructor.Student">
<constructor-arg value="李华"/>
<constructor-arg value="20"/>
<constructor-arg ref="school"/>
</bean> --> <!-- 方式三：推荐-->
<bean id="student" class="com.ietree.spring.basic.di.constructor.Student">
<constructor-arg name="name" value="李华"/>
<constructor-arg name="age" value="20"/>
<constructor-arg name="school" ref="school"/>
</bean> </beans>
个人强烈推荐使用方式三，因为这样的配置方式不会带来歧义，关键是可读性比强两者要强。
测试：
@Test
public void test01(){ String resource = "com/ietree/spring/basic/di/constructor/applicationContext.xml";
ApplicationContext ctx = new ClassPathXmlApplicationContext(resource); Student student = (Student) ctx.getBean("student");
System.out.println(student);
}
程序输出：
Student [name=李华, age=20, school=School [name=北京大学]]
二、命名空间注入
命名空间注入分为两种，p命名空间和c命名空间。
例：
创建School类：
/**
* 学校类
*
* @author Root
*/
public class School { private String name; public School(String name) {
super();
this.name = name;
} public void setName(String name) {
this.name = name;
} @Override
public String toString() {
return "School [name=" + name + "]";
} }
创建学生类（Student）：
/**
* 学生类
*
* @author Root
*/
public class Student { private String name;
private int age;
// 对象属性，也叫做域属性
private School school; public Student() {
super();
} public Student(String name, int age, School school) {
super();
this.name = name;
this.age = age;
this.school = school;
} public void setName(String name) {
System.out.println("执行setName()");
this.name = name;
} public void setAge(int age) {
System.out.println("执行setAge()");
this.age = age;
} public void setSchool(School school) {
this.school = school;
} @Override
public String toString() {
return "Student [name=" + name + ", age=" + age + ", school=" + school + "]";
} }
配置文件：
<?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" xmlns:c="http://www.springframework.org/schema/c" xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- 注册School -->
<!-- <bean id="mySchool" class="com.ietree.spring.basic.di.namespace.School" p:name="清华大学"/> 注册Student
<bean id="student" class="com.ietree.spring.basic.di.namespace.Student" p:name="李华" p:age="20" p:school-ref="mySchool"/> --> <!-- 注册School -->
<bean id="mySchool" class="com.ietree.spring.basic.di.namespace.School" c:name="清华大学"/> <!-- 注册Student -->
<bean id="student" class="com.ietree.spring.basic.di.namespace.Student" c:name="李华" c:age="20" c:school-ref="mySchool"/> </beans>
注意：
1、这里如果要想使用这两种命名空间方式的话，需要先导入约束：
xmlns:p="http://www.springframework.org/schema/p"
xmlns:c="http://www.springframework.org/schema/c"
2、如果是使用c命名空间的方式的话，在类里面还必须写上带参构造器。
三、集合属性注入
创建School类：
/**
* 学校类
*
* @author Root
*/
public class School { private String name; public void setName(String name) {
this.name = name;
} @Override
public String toString() {
return "School [name=" + name + "]";
} }
创建Some类：
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set; public class Some {
private School[] schools;
private String[] myStr;
private List<String> myList;
private Set<String> mySet;
private Map<String, Object> myMap;
private Properties myProps; public void setSchools(School[] schools) {
this.schools = schools;
} public void setMyStr(String[] myStr) {
this.myStr = myStr;
} public void setMyList(List<String> myList) {
this.myList = myList;
} public void setMySet(Set<String> mySet) {
this.mySet = mySet;
} public void setMyMap(Map<String, Object> myMap) {
this.myMap = myMap;
} public void setMyProps(Properties myProps) {
this.myProps = myProps;
} @Override
public String toString() {
return "Some [schools=" + Arrays.toString(schools) + ", myStr=" + Arrays.toString(myStr) + ", myList=" + myList
+ ", mySet=" + mySet + ", myMap=" + myMap + ", myProps=" + myProps + "]";
} }
配置applicationContext.xml文件：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- 注册School -->
<bean id="mySchool" class="com.ietree.spring.basic.di.list.School">
<property name="name" value="北京大学"></property>
</bean>
<bean id="mySchool2" class="com.ietree.spring.basic.di.list.School">
<property name="name" value="清华大学"></property>
</bean> <!-- 注册Student -->
<bean id="some" class="com.ietree.spring.basic.di.list.Some">
<property name="schools">
<array>
<ref bean="mySchool"/>
<ref bean="mySchool2"/>
</array>
</property>
<property name="myStr">
<array>
<value>中国</value>
<value>广东</value>
</array>
</property>
<property name="myList">
<list>
<value>深圳</value>
<value>龙岗</value>
</list>
</property>
<property name="mySet">
<set>
<value>坂田</value>
<value>天安云谷</value>
</set>
</property>
<property name="myMap">
<map>
<entry key="mobile" value="123456"></entry>
<entry key="weChat" value="654321"></entry>
</map>
</property>
<property name="myProps">
<props>
<prop key="edu">本科</prop>
<prop key="gender">性别</prop>
</props>
</property>
</bean> </beans>
方式二：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- 注册School -->
<bean id="mySchool" class="com.ietree.spring.basic.di.list.School">
<property name="name" value="北京大学"></property>
</bean>
<bean id="mySchool2" class="com.ietree.spring.basic.di.list.School">
<property name="name" value="清华大学"></property>
</bean> <!-- 注册Student -->
<bean id="some" class="com.ietree.spring.basic.di.list.Some">
<property name="schools">
<array>
<ref bean="mySchool"/>
<ref bean="mySchool2"/>
</array>
</property> <property name="myStr" value="中国,广东"/> <property name="myList" value="深圳,龙岗"/> <property name="mySet" value="坂田,天安云谷"/> <property name="myMap">
<map>
<entry key="mobile" value="123456"></entry>
<entry key="weChat" value="654321"></entry>
</map>
</property>
<property name="myProps">
<props>
<prop key="edu">本科</prop>
<prop key="gender">性别</prop>
</props>
</property>
</bean> </beans>
四、对于域属性的自动注入
<!-- 注册Student
autowire="byName"：通过字段名注入
autowire="byType"：通过字段类型注入
-->
<bean id="student" class="com.ietree.spring.basic.di.domain.Student" autowire="byName">
<property name="name" value="李华"></property>
<property name="age" value="20"></property>
</bean>
五、使用SPEL注入
SPEL，Spring Expression Language，即Spring EL表达式语言。即，在Spring配置文件中为Bean属性注入值时，可直接使用SPEL表达式计算的结果。SPEL表达式以#开头，后跟一对大括号。
举例：
创建Person类：
package com.ietree.spring.basic.di.spel;
public class Person {
private String pname;
private int page;
public Person() {
super();
}
public void setPname(String pname) {
this.pname = pname;
}
public void setPage(int page) {
this.page = page;
}
public String getPname() {
return pname;
}
public int getPage() {
return page;
}
public int computeAge() {
return this.page > 25 ? 25 : this.page;
}
@Override
public String toString() {
return "Person [pname=" + pname + ", page=" + page + "]";
}
}
创建Student类：
package com.ietree.spring.basic.di.spel; /**
* 学生类
*
* @author Root
*/
public class Student { private String name; private int age; public Student() {
super();
} public void setName(String name) {
this.name = name;
} public void setAge(int age) {
this.age = age;
} @Override
public String toString() {
return "Student [name=" + name + ", age=" + age + "]";
} }
配置ApplicationContext.xml文件：<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"> <bean id="myPerson" class="com.ietree.spring.basic.di.spel.Person">
<property name="pname" value="李华"></property>
<!-- 随机生成0 - 99数字 -->
<property name="page" value="#{T(java.lang.Math).random() * 100}"></property>
</bean> <bean id="myStudent" class="com.ietree.spring.basic.di.spel.Student">
<property name="name" value="#{myPerson.pname}"></property>
<!-- <property name="age" value="#{myPerson.page > 25 ? 25 : myPerson.page}"></property> -->
<property name="age" value="#{myPerson.computeAge() }"></property>
</bean> </beans>
六、使用内部Bean注入
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- 注册School -->
<!-- <bean id="school" class="com.ietree.spring.basic.di.inner.School">
<property name="name" value="北京大学"></property>
</bean> --> <!-- 注册Student -->
<bean id="student" class="com.ietree.spring.basic.di.inner.Student">
<property name="name" value="李华"></property>
<property name="age" value="20"></property>
<property name="school">
<bean class="com.ietree.spring.basic.di.inner.School">
<property name="name" value="清华大学"></property>
</bean>
</property>
</bean> </beans>
七、使用同类抽象Bean注入
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- 同类抽象Bean -->
<bean id="baseStudent" class="com.ietree.spring.basic.di.sameextends.Student" abstract="true">
<property name="school" value="清华大学"/>
<property name="department" value="计算机系"/>
</bean>
<bean id="student1" parent="baseStudent">
<property name="name" value="小明"/>
<property name="age" value="21"/>
</bean>
<bean id="student2" parent="baseStudent">
<property name="name" value="张三"/>
<property name="age" value="22"/>
</bean>
<bean id="student3" parent="baseStudent">
<property name="name" value="李四"/>
<property name="age" value="23"/>
</bean> </beans>
八、使用异类抽象Bean注入
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- 异类抽象Bean -->
<bean id="baseStudent" abstract="true">
<property name="school" value="清华大学"/>
<property name="department" value="计算机系"/>
</bean> <bean id="student" class="com.ietree.spring.basic.di.sameextends.Student" parent="baseStudent">
<property name="name" value="小明"/>
<property name="age" value="21"/>
</bean>
<bean id="teacher" class="com.ietree.spring.basic.di.sameextends.Teacher" parent="baseStudent">
<property name="name" value="李四"/>
<property name="age" value="23"/>
</bean> </beans>
九、为应用指定多个Spring配置文件
1、同级关系：
测试：
package com.ietree.spring.basic.di.mulxml; import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext; public class MyTest { @Test
public void test01() { /*String resource1 = "com/ietree/spring/basic/di/setter/spring-base.xml";
String resource2 = "com/ietree/spring/basic/di/setter/spring-beans.xml";
ApplicationContext ctx = new ClassPathXmlApplicationContext(resource1, resource2);*/ String resource = "com/ietree/spring/basic/di/setter/spring-*.xml";
ApplicationContext ctx = new ClassPathXmlApplicationContext(resource); Student student = (Student) ctx.getBean("student");
System.out.println(student);
} }
2、包含关系：
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd"> <import resource="classpath:com/ietree/spring/basic/di/mulxml/spring-base.xml"/>
<import resource="classpath:com/ietree/spring/basic/di/mulxml/spring-beans.xml"/>
</beans>
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思路 1. 经典解法是用环形链表模拟圆圈, 然后每次减少一个节点. 时间复杂度为 o(mn), 空间复杂度为 o(n) 2. 转化成数学问题, 递推公式决定下一个元素. 时间复杂度为 o(n), 空间 ...
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