踩过的小坑

前几天上了个小需求，出现了一个空指针的bug
项目中有个抽象基类 abstractBase 里面有很多私有的bean，这个基类有多个实现类ClassA，ClassB等等，其中ClassA中也有跟基类同名的私有属性bean，并且实现了get、set方法，结果导致在基类中用这个bean时报了空指针。
例如：
抽象基类：BaseRepaireService

public abstract class BaseRepaireService implements RepaireService{
    private InvoiceService invoiceService;
    private String title;

    public abstract void print();
    public void invoice(){
        print();
        invoiceService.makeInvoice("维修发票");
    }
    public InvoiceService getInvoiceService() {
        return invoiceService;
    }
    public void setInvoiceService(InvoiceService invoiceService) {
        this.invoiceService = invoiceService;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
}

具体实现类：OfsRepaireServiceImpl

public class OfsRepaireServiceImpl extends BaseRepaireService {
    
    private InvoiceService invoiceService;
    @Override
    public void print() {
        invoiceService.makeInvoice("外单维修");
    }
    @Override
    public void makeRepaireInvoice(){
        super.invoice();
    }
    @Override
    public InvoiceService getInvoiceService() {
        return invoiceService;
    }
    @Override
    public void setInvoiceService(InvoiceService invoiceService) {
        this.invoiceService = invoiceService;
    }
}

配置文件：

    <bean id="ofsRepaireService" class="com.xc.service.impl.OfsRepaireServiceImpl"/>
    <bean id="invoiceService" class="com.xc.service.impl.InvoiceServiceImpl"/>

测试方法：

    @Test
    public void repaireServiceTest(){
        ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
        RepaireService ofsRepaireService = (RepaireService) context.getBean("ofsRepaireService");
        ofsRepaireService.makeRepaireInvoice();
    }

运行测试方法 报错：
java.lang.NullPointerException
at com.xc.service.BaseRepaireService.invoice(BaseRepaireService.java:17)
at com.xc.service.impl.OfsRepaireServiceImpl.makeRepaireInvoice(OfsRepaireServiceImpl.java:19)
at SrpingParentClassTest.repaireServiceTest(SrpingParentClassTest.java:23)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
在执行基类的 invoiceService.makeInvoice("维修发票"); 语句是抛出的空指针
因为子类重写了基类的get set方法，spring在注入属性的时候实际上是将invoiceService注入到了子类的属性上 而非父类的属性上，所以父类执行时会爆出空指针
可以改成子类里面不重写父类的get set方法 直接调用父类的方法执行：

public class OfsRepaireServiceImpl extends BaseRepaireService {

    private InvoiceService invoiceService;
    @Override
    public void print() {
        super.getInvoiceService().makeInvoice("外单维修");
    }

    @Override
    public void makeRepaireInvoice(){
        super.invoice();
    }

//    @Override
//    public InvoiceService getInvoiceService() {
//        return invoiceService;
//    }
//
//    @Override
//    public void setInvoiceService(InvoiceService invoiceService) {
//        this.invoiceService = invoiceService;
//    }
}

或者不修改子类而是将基类中的属性用@Resource注解：

public abstract class BaseRepaireService implements RepaireService{

    @Resource
    private InvoiceService invoiceService;

    private String title;

    public abstract void print();
    public void invoice(){
        print();
        invoiceService.makeInvoice("维修发票");
    }
    public InvoiceService getInvoiceService() {
        return invoiceService;
    }
    public void setInvoiceService(InvoiceService invoiceService) {
        this.invoiceService = invoiceService;
    }
    public String getTitle() {
        return title;
    }
    public void setTitle(String title) {
        this.title = title;
    }
}