Spring相当于一个 超级工厂，Bean就相当于工厂里每一个机器。Spring的 Ioc容器生产并管理Bean。因此如果我们想要在项目中使用这个工厂，就需要对Spring的配置文件进行配置。
Spring容器支持XML和Properties两种格式的配置文件，常见是使用前者。 在Spring容器中，XML配置 文件的根元素是< beans>,< beans>中包含多个< bean>,每一个< bean>就定义了一个Bean。
< bean >元素常用属性及子元素
Bean的实例化主要通过该Bean对应实现类的无参构造器来。
Course类
package club.johnny.polo; public class Course { private String courseName; private int courseHour ; public Course() {//此无参构造器必须存在 才能通过构造器实例化该Bean } public Course(String courseName, int courseHour) { this.courseName = courseName; this.courseHour = courseHour; this.teacher = teacher; } public String getCourseName() { return courseName; } public void setCourseName(String courseName) { this.courseName = courseName; } public int getCourseHour() { return courseHour; } public void setCourseHour(int courseHour) { this.courseHour = courseHour; } } <?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:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd"> <bean id="courseDemo" class="club.johnny.polo.Course"> </bean> </beans> 注意： 若想通过XML形式获取该类的实例化对象，则该类的无参构造器 必须存在，即 public Course() { }Bean的装配方式也就是注入依赖。依赖注入作用就是在使用Spring 框架创建对象时，动态地将其所依赖的对象注入Bean组件中。
主要有以下三种方式：
一、基于XML配置 二、基于注解（最常用） 三、自动装配
Spring提供了两种基于XML的装配：设值注入和构造注入。
1、 setter注入：通过setXxx()赋值注入被依赖的实例。通过调用无参的构造器实例化Bean，然后通过反射的方式ByName调用该Bean对象的setter方法实现setter方法的注入。因此设值注入必须满足以下两点要求：
Bean的实现类必须提供一个默认的无参构造方法Bean的实现类必须为需注入的属性 提供setter方法 <bean id="bean的唯一标识" class="实现类" ...> <property name="实体类的私有属性名"> .... </property> </bean>2、构造器注入：通过构造方法赋值
<bean id="bean的唯一标识" class="实现类" ...> <constructor-arg value="值" type="实体类的私有属性类型" index="该属性在构造方法的下标索引" name="实体类的私有属性名"></constructor-arg> .... <constructor-arg value="值" type="实体类的私有属性类型" index="该属性在构造方法的下标索引" name="实体类的私有属性名"></constructor-arg> </bean>如果 < constructor-arg >的顺序与构造方法参数的顺序不一致，则需要通过type或者index或name指定。
以集合类为例
AllCollection类
package club.johnny.polo; import java.util.List; import java.util.Map; import java.util.Properties; import java.util.Set; public class AllCollection { private String [] arrayElement; private Set<String> setElement; private List<String> listElement; private Map<String,String> mapElement; private Properties propsElement ; public Properties getPropsElement() { return propsElement; } public void setPropsElement(Properties propsElement) { this.propsElement = propsElement; } public void setListElement(List<String> listElement) { this.listElement = listElement; } public String[] getArrayElement() { return arrayElement; } public void setArrayElement(String[] arrayElement) { this.arrayElement = arrayElement; } public Set<String> getSetElement() { return setElement; } public void setSetElement(Set<String> setElement) { this.setElement = setElement; } public List getListElement() { return listElement; } public Map<String, String> getMapElement() { return mapElement; } public void setMapElement(Map<String, String> mapElement) { this.mapElement = mapElement; } @Override public String toString() { // TODO Auto-generated method stub String s=""; for(String as:arrayElement) s+=as+" "; return "list:" + listElement.toString()+"\nset:"+setElement.toString()+"\nmap:"+ mapElement.toString()+"\narray:"+s+"\npropsElement:"+propsElement.toString(); } }applicationContext.xml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:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd"> <bean id="collectionDemo" class="club.johnny.polo.AllCollection"> <property name="listElement"> <list> <value>苹果</value> <value>香蕉</value> <value>水蜜桃</value> </list> </property> <property name="setElement"> <set> <value>苹果2</value> <value>香蕉2</value> <value>水蜜桃2</value> </set> </property> <property name="mapElement"> <map> <entry> <key><value>apple</value></key> <value>苹果3</value> </entry> <entry> <key><value>banana</value></key> <value>香蕉3</value> </entry> <entry> <key><value>peach</value></key> <value>水蜜桃3</value> </entry> </map> </property> <property name="arrayElement"> <array> <value>苹果4</value> <value>香蕉4</value> <value>水蜜桃4</value> </array> </property> <property name="propsElement"> <props> <prop key="apple5">苹果5</prop> <prop key="banana5">香蕉5</prop> <prop key="peach5">水蜜桃5</prop> </props> </property> </bean> </beans>注意： set、list、数组 各自都有自己的标签 ，但是也可以用< list> 代替以上三种。
Course类
package club.johnny.polo; public class Course { private String courseName; private int courseHour ; private Teacher teacher ;//授课老师 ，依赖于Teacher public Course() { } public Course(Teacher teacher) { this.teacher = teacher; } public Course(String courseName, int courseHour, Teacher teacher) { this.courseName = courseName; this.courseHour = courseHour; this.teacher = teacher; } public String getCourseName() { return courseName; } public void setCourseName(String courseName) { this.courseName = courseName; } public int getCourseHour() { return courseHour; } public void setCourseHour(int courseHour) { this.courseHour = courseHour; } public Teacher getTeacher() { return teacher; } public void setTeacher(Teacher teacher) { this.teacher = teacher; } public void showInfo() { System.out.println(this.courseName+","+this.courseHour+","+this.teacher.getName()); } }Teacher类
package club.johnny.polo; public class Teacher { private String name; private int age ; public Teacher() { } public Teacher(int age) { this.age = age; } public Teacher(String name) { this.name = name; } /* public Teacher(String name, int age) { this.name = name; this.age = age; } */ public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } }test测试类
package club.johnny.test; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import club.johnny.polo.Course; import club.johnny.polo.AllCollection; public class Test { public static void testConstructor() { ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml"); Course course =(Course) context.getBean("courseDemo"); course.showInfo(); } public static void main(String[] args) { testConstructor(); } } <?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:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd"> <!-- 构造器 注入 --> <bean id="myteacher" class="club.johnny.polo.Teacher"> <!-- 通过私有属性名指定 --> <constructor-arg name="name" value="johnnylin"></constructor-arg> </bean> <bean id="courseDemo" class="club.johnny.polo.Course"> <!-- 可以严格按照构造器的顺序也可以 --> <constructor-arg index="0" value="java语言"></constructor-arg> <constructor-arg index="1" value="15"></constructor-arg> <constructor-arg name="teacher" ref="myteacher"></constructor-arg> </bean> </beans>给对象类型赋值为null,注意没有子标签< value >
<property name="属性名"> <null/> </property>给属性赋值为 “”
<property name="类的私有属性名" value=""> </property>或者
<property name="类的私有属性名" > <value></value> </property>总结： IOC容器赋值：如果是简单类型（8个基本+String），则使用
< property name="" value="8个基本数据类型"> < /property>如果是对象类型，ref=“需要引用的id值”，因此实现了 对象与对象之间的依赖关系
<property name="" ref="需要引用的id值""> </property>Spring中定义了一系列的注解，常用的有以下：
注解作用层/作用三层组件@RepositoryDao层@ServiceService层@ControllerController层@Component当不知道该类属于三层的那一层 时，可以使用@Component代替@AutoWired用于对Bean的属性变量、属性的setter方法及构造方法进行标注完成自动装配，默认按Bean的类型进行装配@Qualifier与@AutoWired配合使用，会将默认的按Bean类型装配改为按名装配@Resource与@AutoWired注解功能一致，name参数指定属性名，type参数指定属性类型，默认name，不匹配再typeStudent实体类
package club.johnny.polo; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Student { private int stuNo ; private String stuName ; private int stuAge ; public int getStuNo() { return stuNo; } public void setStuNo(int stuNo) { this.stuNo = stuNo; } public String getStuName() { return stuName; } public void setStuName(String stuName) { this.stuName = stuName; } public int getStuAge() { return stuAge; } public void setStuAge(int stuAge) { this.stuAge = stuAge; } @Override public String toString() { return this.stuNo+","+this.stuName+","+this.stuAge; } }IStudent接口
package club.johnny.dao; import club.johnny.polo.Student; public interface IStudentDao { public void addStudent(Student student); }IStudent接口的实现类StudentDao
package club.johnny.dao.impl; import org.springframework.stereotype.Repository; import club.johnny.dao.IStudentDao; import club.johnny.polo.Student; //相当于在XML：<bean id="studentDao" class="club.johnny.dao.impl.StudentDaoImpl"></bean> @Repository("studentDao") public class StudentDaoImpl implements IStudentDao { public void addStudent(Student student) { System.out.println("调用dao层，添加学生……"); } }IStudentService 接口
package club.johnny.service; import club.johnny.polo.Student; public interface IStudentService { public void addStudent(Student student); }IStudentService 实现类StudentServiceImpl
package club.johnny.service.impl; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.beans.factory.annotation.Qualifier; import org.springframework.stereotype.Service; import club.johnny.dao.impl.StudentDaoImpl; import club.johnny.polo.Student; import club.johnny.service.IStudentService; 相当于在XML：<bean id="studentService" class="club.johnny.service.impl.StudentServiceImpl"></bean> @Service("studentService") public class StudentServiceImpl implements IStudentService{ // @Resource("studentDao") 与下面两句效果等效 //相当于<property name="studentDao" ref="studentDao"></property> // @Autowired // @Qualifier(value="studentDao") //@Qualifier的value参数指定按值装配 @Autowired //@Autowired默认按类型装配 private StudentDaoImpl studentDao; public void addStudent(Student student) { this.studentDao.addStudent(student); System.out.println("调用service层，添加学生……"); } } 注意： 基于注解方式装配要在配置文件applicationContext.xml中配置扫描器 <?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:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd"> <!-- 配置扫描器 --> <context:component-scan base-package="club.johnny"></context:component-scan> </beans>test测试类
package club.johnny.test; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; import club.johnny.polo.Course; import club.johnny.polo.Student; import club.johnny.dao.impl.StudentDaoImpl; import club.johnny.polo.AllCollection; public class Test { public static void testAnnotation() { ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml"); StudentServiceImpl studentService = (StudentServiceImpl)context.getBean("studentService"); studentService.addStudent(new Student()); } public static void main(String[] args) { testAnnotation(); } }结果：
在applicationContext.xml文件中
<bean ... class="" autowire="byName|byType|constructor|no" > </bean> 属性值含义byName根据名称自动装配，自动寻找容器中其他bean的id值等于该实现类属性的byType根据类型自动装配，自动寻找容器中其他bean的类型值与该实现类属性的类型相同的constructor根据构造函数进行byType自动装配no在默认情况下不使用自动装配，Bean依赖注入必须通过ref实现可以在全局区设置 default-autowire=“byName|byType”
自动装配虽然可以减少代码量，但是会降低程序的可读性，使用时需要谨慎。