Spring注入和new对象产生的错误场景
问题:
@Autowired注入Spring Bean,则当前类必须也是Spring Bean才能调用它,不能用new xxx()来获得对象,这种方式获得的对象无法调用@Autowired注入的Bean。
1、类1,加入Spring Pool
public class PersonServiceImpl implements PersonService{
public void save(){
System.out.println("This is save for test spring");
}
public List<String> findAll(){
List<String> retList = new ArrayList<String>();
for(int i=1;i<10;i++){
retList.add("test"+i);
}
return retList;
}
}
//加入Spring Bean容器中
<bean id="personServiceImpl" class="com.machome.testtip.impl.PersonServiceImpl" >
</bean>
2、类2,@Autowired类1,并且也加入Spring Pool
public class ProxyPServiceImpl implements ProxyPService {
public void save(){
System.out.print("this is proxy say:");
personService.save();
}
public List<String> findAll(){
System.out.print("this is proxy say:");
return personService.findAll();
}
@Autowired
PersonService personService;
}
```java
3、直接new类2,则执行其方法时出null pointer错误
> 在使用spring框架注解的时候,不能在通过new关键字去实例化全局变量。如果两者并存的情况下,spring注入对象会失败,相应的引用会为空,后台就会报空指针异常
ProxyPService proxyPService = new ProxyPServiceImpl();
proxyPService.save();
执行报错:
java.lang.NullPointerException
at com.machome.testtip.impl.ProxyPServiceImpl.save(ProxyPServiceImpl.java:18)
at com.machome.testtip.TestSpring2.testSave(TestSpring2.java:34)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
4、解决:用Spring方式获取类2的Bean,再执行其方法,没问题
ProxyPService proxyPService = null;
try {
String[] confFile = {"spring.xml"};
ctx = new ClassPathXmlApplicationContext(confFile);
proxyPService = (ProxyPService)ctx.getBean("ProxyPServiceImpl");
} catch (Exception e) {
e.printStackTrace();
}
proxyPService.save();
执行:
this is proxy say:This is save for test spring
一般的话这属于一个特殊场景,如果需要的话就获取它的bean即可,但是现在springboot已经封装好了所以不必要管这些,遵从开发规则。