验证类：
public class Validator
{
private XxxService xxxService;
public void validate()
{
xxxService.xxxx();
}
public XxxService getXxxService()
{
return xxxService;
}
public void setXxxService(XxxService xxxService)
{
this.xxxService = xxxService;
}
}
调用代码：
Validator validator=new Validator();
//实际调用过程中漏写的代码
validator.setXxxService(service);
validator.validate();
有时会忘记set service而导致空指针异常，正确的处理方式应是将setService的代码写到构造函数中。
正确的验证类：
public class Validator
{
private XxxService xxxService;
public Validator(XxxService xxxService)
{
this.xxxService = xxxService;
}
public void validate()
{
xxxService.xxxx();
}
}
调用：
Validator validator=new Validator(service);
validator.validate();