how to provide string constants for drop down lists in jsp

问题

In a jsp page ,I am presenting the customer with drop down lists to select creditcardtype,expiration month,expiration year of credit card. I am looking at ways the necessary strings for this can be put ,other than hardcoding them in html.

thanks

mark

<tr>
<td>
    <select id="creditCardType" title="select card type" name="creditCardType">
        <option value="M0">MasterCard</option>
        <option value="D0">Discover</option>
        <option value="J0">JCB</option>
        <option value="I0">Diners Club</option>
        <option value="A0">American Express</option>
        <option value="V0">Visa</option>
        <option value="V">Amazon.com Visa</option>
        <option value="G21">Amazon.com Store Card</option>
    </select>
</td>
</tr>
<tr>
<td>Expiration Date</td>
<td> 
                     <select id="cardexpiryMonth" name="cardexpiryMonth">
                        <option value="01" selected="selected">01</option>
                        <option value="02" >02</option>
                        <option value="03" >03</option>
                        <option value="04" >04</option>
                        <option value="05" >05</option>
                        <option value="06" >06</option>
                        <option value="07" >07</option>
                        <option value="08" >08</option>
                        <option value="09" >09</option>
                        <option value="10" >10</option>
                        <option value="11" >11</option>
                        <option value="12" >12</option>
                      </select>
</td>
<td>
                    <select id="cardexpiryYear" name="cardexpiryYear">
                        <option value="2011" >2011</option>
                        <option value="2012" selected="selected">2012</option>
                        <option value="2013" >2013</option>
                        <option value="2014" >2014</option>
                        <option value="2015" >2015</option>
                        <option value="2016" >2016</option>
                        <option value="2017" >2017</option>
                        <option value="2018" >2018</option>
                        <option value="2019" >2019</option>
                        <option value="2020" >2020</option>
                        <option value="2021" >2021</option>
                        <option value="2022" >2022</option>
                        <option value="2023" >2023</option>
                        <option value="2024" >2024</option>
                        <option value="2025" >2025</option>
                        <option value="2026" >2026</option>

                        <option value="2027" >2027</option>
                        <option value="2028" >2028</option>
                        <option value="2029" >2029</option>
                        <option value="2030" >2030</option>
                        <option value="2031" >2031</option>
                      </select>
</td>
</tr>

回答1:

If it are application wide constants, just put them in the application scope during application startup. The application scope is represented by the object being an attribute of ServletContext. See also How do servlets work? Instantiation, sessions, shared variables and multithreading

CDI available?

If CDI happens to be available in your environment (i.e. you're running a normal JEE server such as WildFly, Payara, TomEE, etc), then just use an @ApplicationScoped bean instead of a ServletContextListener.

@Named @ApplicationScoped
public class Data {

    private Map<String, String> creditCardTypes;

    @PostConstruct
    public void init() { 
        creditCardTypes = new LinkedHashMap<String, String>();
        creditCardTypes.put("M0", "MasterCard");
        creditCardTypes.put("D0", "Discover");
        // ...
    }

    public Map<String, String> getCreditCardTypes() {
        return creditCardTypes;
    }
}

(note that I used LinkedHashMap as it maintains insertion order in contrary to HashMap)

This way it's available as ${data.creditCardTypes} by EL in any JSP. You can then use JSTL <c:forEach> to iterate over it. It also supports iterating over a Map and each iteration will give a Map.Entry back which in turn has getKey() and getValue() methods which are accessible in EL as well.

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
...
<select id="creditCardType" title="select card type" name="creditCardType">
    <c:forEach items="${data.creditCardTypes}" var="creditCardType">
        <option value="${creditCardType.key}">${creditCardType.value}</option>
    </c:forEach>
</select>

No CDI available?

If CDI is not available (i.e. you're not running a normal JEE server, such as Tomcat, Jetty, Undertow, etc, and you don't want to install CDI for some reason), then you can use the init() method of an arbitrary servlet or, better, a ServletContextListener.

@WebListener
public class Data implements ServletContextListener {

    private Map<String, String> creditCardTypes;

    @Override
    public void contextInitialized(ServletContextEvent event) { 
        creditCardTypes = new LinkedHashMap<String, String>();
        creditCardTypes.put("M0", "MasterCard");
        creditCardTypes.put("D0", "Discover");
        // ...

        event.getServletContext().setAttribute("data", this);
    }

    public Map<String, String> getCreditCardTypes() {
        return creditCardTypes;
    }
}

This way it's also available as ${data.creditCardTypes} by EL in any JSP.

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
...
<select id="creditCardType" title="select card type" name="creditCardType">
    <c:forEach items="${data.creditCardTypes}" var="creditCardType">
        <option value="${creditCardType.key}">${creditCardType.value}</option>
    </c:forEach>
</select>

回答2:

If you're using Spring (2.5/3.0) then have a look at @ModelAttribute

来源：https://stackoverflow.com/questions/6659986/how-to-provide-string-constants-for-drop-down-lists-in-jsp