Spring或者Spring启动中没有类型的 Bean
时间：2020-02-23 14:34:36 来源:igfitidea点击:
在本教程中，我们将看到一个例外：没有类型的 Bean类。
springframework.beans.factory.nosuchbeandefinitionException：没有限定 Bean类？
让我们看看有哪些原因
理由1：你忘了声明 Bean。
让我们在举例的帮助下了解这一点。
XML配置
1.创建一个简单的Java Maven项目。
2.
Maven依赖性将Spring和Cglib Maven依赖于Pom.xml。
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>${spring.version}</version>
</dependency>
<!-- cglib required for @configuration annotation -->
<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>3.0</version>
</dependency>
</dependencies>
<properties>
<spring.version>4.2.1.RELEASE</spring.version>
</properties>
所以你的pom.xml看起来像：
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"<
<modelVersion<4.0.0</modelVersion>
<groupId>org.igi.theitroad</groupId>
<artifactId>SpringHelloWorldJavaBasedConfiguration</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>SpringHelloWorldJavaBasedConfiguration</name>
<description>It provides hello world program for java based config
</description>
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>${spring.version}</version>
</dependency>
<!-- cglib required for @configuration annotation -->
<dependency>
<groupId>cglib</groupId>
<artifactId>cglib</artifactId>
<version>3.0</version>
</dependency>
</dependencies>
<properties>
<spring.version>4.2.1.RELEASE</spring.version>
</properties>
</project>
3.创建bean类
在package org.igi.theitroad中创建一个名为x.java的bean类。
package org.igi.theitroad;
import org.springframework.beans.factory.annotation.Autowired;
public class X {
@Autowired
Y y;
public Y getY() {
return y;
}
public void setY(Y y) {
this.y = y;
}
}
请注意，我们使用自动注释注释在x中注入bean y。
在package org.igi.theitroad中创建一个名为y.java的 Bean类类。
package org.igi.theitroad;
public class Y {
public void methodY()
{
System.out.println("In method Y");
}
}
- ApplicationContext.xml在SRC/Main/Resources中创建ApplicationContext.xml，如下所示。
<?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
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd">
<bean id="x" class="org.igi.theitroad.X">
</bean>
<context:annotation-config
</beans>
我们刚刚在此介绍了一个bean x 5.创建SpringApplicationMain.java
package org.igi.theitroad;
import org.springframework.context.support.ClassPathXmlApplicationContext;
/**
*
* Spring Application main
*/
public class SpringApplicationMain
{
public static void main( String[] args )
{
ClassPathXmlApplicationContext ac = new ClassPathXmlApplicationContext("ApplicationContext.xml");
X firstX = (X) ac.getBean("x");
Y firstY = firstX.getY();
ac.close();
}
}
6.在运行上面的程序时运行它，我们将得到以下输出。
.
.
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.igi.theitroad.Y] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
.
.
正如我们所看到的，我们获得了nosuchbeandefinitionException：没有XML中没有声明的bean"y"的类型的合格 Bean。
Java配置
前2个步骤保持不变。
让我们将@Component添加到X.
java.
package org.igi.theitroad;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
@Component
public class X {
@Autowired
Y y;
public Y getY() {
return y;
}
public void setY(Y y) {
this.y = y;
}
}
在package org.igi.theitroad中创建一个名为y.java的 Bean类类。
package org.igi.theitroad;
public class Y {
public void methodY()
{
System.out.println("In method Y");
}
}
4.创建ApplicationConfiguration.java，如下所示。
package org.igi.theitroad;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan("org.igi.theitroad")
public class ApplicationConfiguration {
}
5.创建主类
package org.igi.theitroad;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;;
public class SpringJavaConfigMain {
public static void main(String[] args) {
@SuppressWarnings("resource")
ApplicationContext appContext = new AnnotationConfigApplicationContext(ApplicationConfiguration.class);
X x = (X) appContext.getBean("x");
Y y = x.getY();
}
}
6.运行它时运行它，我们将得到以下输出。
.
.
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.igi.theitroad.Y] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
.
.
如果将@Component添加到Y.java，则不会发生高于异常。
原因2：我们还没有将包名称添加到@ComponentsCan。
我们可能是在使用@组件，@ service或者@repository，但是与@componentscan的包没有条目。
例如：如果将包名称更改为"org.igi.dummy"，则程序将无法正常工作，即使我们已将@component与bean y汇总。
package org.igi.theitroad;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan("org.igi.dummy")
public class ApplicationConfiguration {
}
原因3：我们有多个候选人用于自动定向
让我们在举例的帮助下了解这一点。
让我们说你一个名为"装饰"的接口
package org.igi.theitroad;
public interface Decorable {
public void decorate();
}
此接口由两个类实现。
curtiandecorator.java.java.
package org.igi.theitroad;
import org.springframework.stereotype.Component;
@Component
public class CurtianDecorator implements Decorable {
@Override
public void decorate() {
System.out.println("Decorating room using curtains");
}
}
walldecorator.java.
package org.igi.theitroad;
import org.springframework.stereotype.Component;
@Component
public class WallDecorator implements Decorable {
@Override
public void decorate() {
System.out.println("Decorating room with wall decorators");
}
}
创建房间.java，它将复合类型接口的参考变量装饰。
package org.igi.theitroad;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
@Component
public class Room {
@Autowired
Decorable decorable;
public Decorable getDecorable() {
return decorable;
}
public void setDecorable(Decorable decorable) {
this.decorable = decorable;
}
}
4.创建ApplicationConfiguration.java，如下所示。
package org.igi.theitroad;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan("org.igi.theitroad")
public class ApplicationConfiguration {
}
5.创建主类
package org.igi.theitroad;
package org.igi.theitroad;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;;
public class SpringJavaConfigMain {
public static void main(String[] args) {
@SuppressWarnings("resource")
ApplicationContext appContext = new AnnotationConfigApplicationContext(ApplicationConfiguration.class);
Room room=(Room)appContext.getBean("room");
Decorable decorable = room.getDecorable();
decorable.decorate();
}
}
6.运行它时运行它，我们将得到以下输出。
. . . Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [org.igi.theitroad.Decorable] is defined: expected single matching bean but found 2: curtianDecorator,wallDecorator . .
请注意，这一次，我们获得了NouniqueBeanDefinitionException，因为有两种自动候选人在室内类中装饰，Spring无法解决哪一个使用。
我们可以使用@qualifier注释来解决此问题。
package org.igi.theitroad;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;
@Component
public class Room {
@Autowired
@Qualifier("wallDecorator")
Decorable decorable;
public Decorable getDecorable() {
return decorable;
}
public void setDecorable(Decorable decorable) {
this.decorable = decorable;
}
}
当我们再次运行该程序时，我们将得到以下输出：
Jun 24, 2016 5:19:36 PM org.springframework.context.annotation.AnnotationConfigApplicationContext prepareRefresh INFO: Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@2e817b38: startup date [Sun Jun 24 17:19:36 IST 2016]; root of context hierarchy Decorating room with wall decorators
