Spring 3 -- NullPointerException from JDBCTemplate.getQueryForMap()

Question

I am running a custom tag in a Spring JSP. I am getting the following error message.

java.lang.NullPointerException
    com.dao.Poll1DAO.getVotes(Poll1DAO.java:27)
    com.tags.Poll1Tag.doTag(Poll1Tag.java:23)
    org.apache.jsp.WEB_002dINF.pages.PollPage_jsp._jspx_meth_myTag1_005fpoll1_005f0(PollPage_jsp.java:602)
    org.apache.jsp.WEB_002dINF.pages.PollPage_jsp._jspService(PollPage_jsp.java:195)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:238)
    org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:262)
    org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1265)
    org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1016)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:965)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:859)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:883)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:781)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

Here is Poll1DAO.getVotes().

public HashMap<String, Object> getVotes() {
    // following line is line 27, referenced in error message
    return (HashMap<String, Object>) this.getJdbcTemplate().queryForMap(
            "select yes, no from poll1 where id = 1");
}

Here is Poll1Tag.doTag().

Poll1DAO poll1DAO = new Poll1DAO();

public void doTag() throws JspException, IOException {
    PageContext pageContext = (PageContext) getJspContext();
    boolean foundCookie = cookieFound();

        pageContext.setAttribute("foundCookiePoll1", foundCookie);
        if (foundCookie) {
            // following line is line 23, referenced in error message
            HashMap<String, Object> poll1Votes = poll1DAO.getVotes();
            pageContext.setAttribute("poll1Yes", (int) poll1Votes.get("yes"));
            pageContext.setAttribute("poll1No", (int) poll1Votes.get("no"));
        }
}

Answer 1

If you are using IoC container such as Spring's application context you should never create managed bean instances by yourself. You always need to pull the instance out from the container - i.e. ApplicationContext. Otherwise they will not be initalized with the necessary dependencies.

Now the question you should ask is - how can I get ApplicationContext instance in a JSP tag class. The answer is simple - just look how the standard Spring tags are doing that (I mean that - go check that link).

// Example on how to obtain bean from JSP tag (ignoring context hierarchy)
WebApplicationContextUtils.getRequiredWebApplicationContext(pageContext.getServletContext()).
        getBeansOfType(Poll1DAO.class).values().iterator().next();