《Pro Spring》学习笔记之依赖解析

发布时间：2020-12-13 20:39:12 所属栏目：百科来源：网络整理

导读：我们有如下两个类： package ch4_alias; public class Course ... { public Course() ... { System.out.println( " incourse " ); } private StringcourseName; public StringgetCourseName() ... { return courseName; } public void setCourseName(Stringc

我们有如下两个类：

package ch4_alias;

public class Course {
publicCourse(){
System.out.println("incourse");
}
privateStringcourseName;

publicStringgetCourseName(){
returncourseName;
}

publicvoidsetCourseName(StringcourseName){
this.courseName=courseName;
}
}

package ch4_alias;

public class Student {
privateStringstuName;
privateCoursestuCourse;
publicStudent(){
System.out.println("instudent");
}
publicCoursegetStuCourse(){
returnstuCourse;
}
publicvoidsetStuCourse(CoursestuCourse){
this.stuCourse=stuCourse;
}
publicStringgetStuName(){
returnstuName;
}
publicvoidsetStuName(StringstuName){
this.stuName=stuName;
}
}

我们用如下的方式进行注入

<? xmlversion="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/beanshttp://www.springframework.org/schema/beans/spring-beans-2.0.xsd" >
< bean id ="student" class ="ch4_alias.Student" >
< property name ="stuName" >
< value > gaoxiang </ value >
</ property >
< property name ="stuCourse" >
< ref bean ="stuCourse" />
</ property >
</ bean >

< bean id ="course" name ="stuCourse" class ="ch4_alias.Course" >
< property name ="courseName" >
< value > shuxu </ value >
</ property >
</ bean >
</ beans >

可以发现，spring为我们首先构造了student,然后再构造course,然后把course注入到student的引用对象中

如果使用depends-on="course"

<? xmlversion="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/beanshttp://www.springframework.org/schema/beans/spring-beans-2.0.xsd" >
< bean id ="student" class ="ch4_alias.Student" depends-on ="course" >
< property name ="stuName" >
< value > gaoxiang </ value >
</ property >
< property name ="stuCourse" >
< ref bean ="stuCourse" />
</ property >
</ bean >

< bean id ="course" name ="stuCourse" class ="ch4_alias.Course" >
< property name ="courseName" >
< value > shuxu </ value >
</ property >
</ bean >
</ beans >

则spring会首先构造course,然后构造student,然后把course注入到student引用对象中

实际开发中，并不建议这样强制决定构造顺序，在将spring代码与遗留系统整合时候，可能会用到depends-on

（编辑：李大同）

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