我试图理解 DI,但是当我使用自动装配和组件注释时,我的 spring bean 没有被注入或创建。相反,我得到一个空指针异常,因为我的 bean 为空。我应该手动创建它吗?在这种情况下在哪里创建?当多个 Bean 相互依赖时,您在哪里指定创建 Bean 的顺序?这是我的代码:
App.java
package se.springtest;
import se.springtest.Person;
import org.springframework.core.io.ClassPathResource;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
public class App
{
public static void main( String[] args )
{
BeanFactory factory = new XmlBeanFactory(
new ClassPathResource("application-context.xml"));
Person p = (Person) factory.getBean("person");
p.show();
}
}
应用程序上下文.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:jdbc="http://www.springframework.org/schema/jdbc"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
<context:component-scan base-package="se.springtest"/>
</beans>
人.java
package se.springtest;
public interface Person {
public void show();
}
PersonImpl.java
package se.springtest;
import org.springframework.stereotype.Component;
import org.springframework.beans.factory.annotation.Autowired;
@Component("person")
public class PersonImpl implements Person {
private String firstName;
private String lastName;
private AdressInfo adress;
public PersonImpl() {firstName="Olle"; lastName="Olsson"; System.out.println("creating PersonImpl object");}
@Autowired
public void setAdress(AdressInfo adress) {
this.adress = adress;
}
public AdressInfo getAdress() {
return adress;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public void show() {
System.out.println("Name is " + getFirstName() + " " +getLastName());
if (adress!=null)
adress.show();
else System.out.println("null");
}
}
地址信息.java
package se.springtest;
public interface AdressInfo {
public void show();
}
AdressInfoImpl.java
package se.springtest;
import org.springframework.stereotype.Service;
@Service("adress")
public class AdressInfoImpl implements AdressInfo {
private String adress;
public AdressInfoImpl() {adress="Storgatan 1"; System.out.println("creating AdressImpl object");}
public String getAdress() {
return adress;
}
public void setAdress(String adr) {
this.adress = adr;
}
public void show() {
System.out.println("Address is " + adress);
}
}
pom.xml
<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/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>se.springtest</groupId>
<artifactId>spring-hello</artifactId>
<packaging>jar</packaging>
<version>1.0-SNAPSHOT</version>
<name>spring-hello</name>
<url>http://maven.apache.org</url>
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<executions>
<execution>
<goals>
<goal>java</goal>
</goals>
</execution>
</executions>
<configuration>
<mainClass>se.springtest.App</mainClass>
</configuration>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>1.5</source>
<target>1.5</target>
</configuration>
</plugin>
</plugins>
</build>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring</artifactId>
<version>2.5.6.SEC02</version>
</dependency>
</dependencies>
</project>
我编译它
mvn clean compile exec:java
但我得到
Name is Olle Olsson
null
代替
Name is Olle Olsson
Adress is Storgatan 1
如果有人能告诉我问题是什么,那将非常有帮助。这会让我和其他人更好地理解 DI...