Java Google guice injector for Servlets返回500错误

这是我的Servlet

@WebServlet("/UserServlet")
public class UserServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    @Inject IUserBusiness userBusiness;


protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    List<UserBean> usersList=new ArrayList<UserBean>();
    usersList=userBusiness.getAllUsers();
    usersList.size();
}

及

但我得到了一个500错误（servlet中userBusiness的null指针异常）

---

如果您使用的是Guice，为什么要设置

@WebServlet（“/UserServlet”）

？额外的注释不会造成任何伤害，但它可能会掩盖一个单独的错误配置

---

确保您是通过Guice绑定访问servlet的，因为如果您是通过其他配置访问servlet，那么@Inject字段将不会被设置，并且在尝试访问它们时，您将获得一个NPE。

UserServlet.java:36上的内容是什么？

public interface IUserBusiness {
    List<UserBean> getAllUsers();
}

public class UserBusiness implements IUserBusiness{

    public List<UserBean>userList;
    public UserBusiness() {
        userList=new ArrayList<UserBean>();
    }
    public List<UserBean> getAllUsers(){
        UserBean user=new UserBean();
        user.setAge(44);
        user.setEmail("fgdfg");
        user.setPassword("dfgdfgf");
        userList.add(user);
        return this.userList;
    }
}

@Override
protected com.google.inject.Injector getInjector() {
    return Guice.createInjector(
            new ServletModule() {
                @Override protected void configureServlets() {
                    serve("/index.html").with(UserServlet.class);
                }
            },
            new Configure());
}

public class Configure extends com.google.inject.AbstractModule{

    @Override
    protected void configure() {
        bind(IUserBusiness.class).to(UserBusiness.class);
    }

}

Servlet.service() for servlet [dynamic.UserServlet] in context with path [/dynamic] threw exception
java.lang.NullPointerException
    at dynamic.UserServlet.doGet(UserServlet.java:36)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)