Question

我有一个servlet类，如下所示

public class test extends HttpServlet {  

private adv1 adv1;
private adv2 adv2;
private adv3 adv3;

...

private adv50 adv50; 

// INITIALIZING REFERENCE VARIABLES 

init() {                      
 ServletContext context = getServletContext();
  adv1 = context.getServletContext("adv1");
  adv2 = context.getServletContext("adv2");
  adv3 = context.getServletContext("adv3");

  ....

  adv50 = context.getServletContext("adv50");

 }

 public void doGet(HttpServletRequest req,HttpServletResponse res) throws java.io.IOException {
    String type = req.getParameter("type");

    // Now what i want is if i get a parameter value as adv2 then i should call a method  in adv2 [eg.adv2.getText()], if parameter value is adv 49 i should call the method in adv 49.[eg adv49.getText()]

   }

}

现在我想要的是如果我得到一个参数值为adv2然后我应该调用adv2中的方法，如果参数值是adv 49我应该调用adv 49中的方法。有没有任何简单的方法来做到这一点而不使用if（req.getParameter（“type”）。equals（“adv2”））{adv2.getText（）;} 50次？

Answer 1

您所拥有的是String，并且您想要查找与其对应的Object。听起来像是我的地图：

// I'm assuming that this interface (or something like it) exists:
public interface Textual {
    String getText();
}

// Then in the servlet...
private Map<String, Textual> advs = new HashMap<String, Textual>(50);

public init() {
    advs.put("adv1", context.getServletContext("adv1"));
    advs.put("adv2", context.getServletContext("adv2"));
    ...
}

public void doGet(HttpServletRequest req,HttpServletResponse res) {
    String type = req.getParameter("type");
    Textual adv = advs.get(type);
    adv.getText(); // do something with this of course...
}

根据配置的脆弱性，重构init方法实现也是一个非常好的主意。例如，定义包含Set，adv1，...的字符串的静态adv2，然后在此集合上使用foreach循环来填充地图。如果您确定ID永远不会更改格式，您甚至可以使用1到50之间的简单循环，每次查找"adv" + i。

Answer 2

您的adv *变量应该扩展公共超类或实现通用接口。因此，请参阅以下代码：

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
    ServletContext context = getServletContext();
    String type = request.getParameter("type");
    Adv adv = (Adv)context.getAttribute(type);
    if(adv != null){
        ...
        // do something with your adv
    }else{
        ...
        // do something else
    }
}

Answer 3

您可以使用反射。如果你的servlet中有方法adv1，adv2等，你可以说：

getClass().getMethod(name).invoke(this);

Answer 4

使用Map<String, TheTypeOfYourAdvVariables>。你的代码片段不正确，所以我想你的意思是

private String adv1;
private String adv2;

public void init() {                      
    ServletContext context = getServletContext();
    adv1 = context.getInitParameter("adv1");
    adv2 = context.getInitParameter("adv2");
}

所以，你可以使用Map<String, String>并像这样填充它：

private Map<String, String> advs = new HashMap<String, String>();

public void init() {                      
    ServletContext context = getServletContext();
    adv1 = context.getInitParameter("adv1");
    advs.put("adv1", adv1);
    adv2 = context.getInitParameter("adv2");
    advs.put("adv2", adv2);
}

然后你可以做

String theAdvType = request.getParameter("type");
String theAdvToUse = advs.get(theAdvType);

请注意，此说明很有用，因为它解释了如何使用地图。但在您的情况下，所有字符串都已存储在servlet上下文中，因此您实际上可以这样做：

String theAdvType = request.getParameter("type");
String theAdvToUse = servletContext.getInitParameter(theAdvType);

如何在java中使用string作为引用变量？

4 个答案: