“选择"未从 List<String> 填充在支柱

2022-01-16 00:00:00 select java jsp struts2 ognl

我有以下来源:

struts.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
    "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
    "http://struts.apache.org/dtds/struts-2.0.dtd">

<struts>

    <constant name="struts.enable.DynamicMethodInvocation" value="true" />
    <constant name="struts.devMode" value="true" />
    <constant name="struts.custom.i18n.resources" value="ApplicationResources" />

    <package name="vislabWebShop" extends="struts-default">

        <action name="UserForward">
            <result>/pages/Login.jsp</result>
        </action>

        <action name="UserLogin" class="vislabWebShop.controller.LoginAction">
            <result name="success">/pages/Welcome.jsp</result>
            <result name="input">/pages/Login.jsp</result>
        </action>

        <action name="UserRegister" class="vislabWebShop.controller.RegisterAction">
            <result name="success">/pages/RegisterSuccess.jsp</result>
            <result name="input">/pages/Register.jsp</result>
        </action>

        <action name="UserRegisterNew">
            <result>/pages/Register.jsp</result>
        </action>

        <action name="UserRegisterSuccess">
            <result>/pages/Login.jsp</result>
        </action>

        <action name="ProductSearchForward">
            <result>/pages/SearchProduct.jsp</result>
        </action>

        <action name="ProductSearch" class="vislabWebShop.controller.ProductSearchAction">
            <result name="success">/pages/Login.jsp</result>
        </action>
    </package>
</struts>

ProductSearchAction.java:

ProductSearchAction.java:

package vislabWebShop.controller;

import java.util.ArrayList;
import java.util.List;

import com.opensymphony.xwork2.ActionSupport;

public class ProductSearchAction extends ActionSupport
{
  private List<String> categories;
  private String chosenCategory;

  public ProductSearchAction()
  {
    categories = new ArrayList<String>();
    categories.add("Eins");
    categories.add("Zwei");
    categories.add("Drei");
  }

  @Override
  public String execute() throws Exception
  {
    return SUCCESS;
  }

  public List<String> getCategories()
  {
    return categories;
  }

  public void setCategories(List<String> categories)
  {
    this.categories = categories;
  }

  public String getChosenCategory()
  {
    return chosenCategory;
  }

  public void setChosenCategory(String chosenCategory)
  {
    this.chosenCategory = chosenCategory;
  }
}

SearchProduct.jsp:

SearchProduct.jsp:

    <%@ page language="java" contentType="text/html; charset=ISO-8859-1"
        pageEncoding="ISO-8859-1"%>
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <%@ taglib prefix="s" uri="/struts-tags"%>

    <html>
    <head>
    <title><s:text name="welcome.title" /></title>
    </head>

    <body bgcolor="white">

        <font color="red"> <s:actionmessage />
        </font>

    <p>
        <b><s:text name="product.search.title" /></b>
    </p>

    <s:form action="ProductSearch" focusElement="description">
        <s:textfield name="description" key="prompt.description" size="20" />
        <s:textfield name="minprice" key="prompt.price.min" size="20" />
        <s:textfield name="maxprice" key="prompt.price.max" size="20" />
        <s:select key="product.search.category" headerKey="-1" 
        headerValue="Bitte wählen Sie eine Kategorie"
            list="categories" />
        <s:submit value="Produkt suchen" align="right" />
    </s:form>

    <font color="red"> <s:actionerror label="label" />
    </font>


</body>
</html>

现在我有一个问题，如果我从 Action ProductSearchForward 转到 JSP 站点 SearchProduct.jsp，我总是会收到以下错误:

Now I have the problem, that I always get the following error if I come from Action ProductSearchForward to the JSP site SearchProduct.jsp:

org.apache.jasper.JasperException:标签选择"，字段列表"，名称产品.search.category":请求的列表键类别"无法解析为集合/数组/映射/枚举/迭代器类型.示例:人或人.{name} - [未知位置]

org.apache.jasper.JasperException: tag 'select', field 'list', name 'product.search.category': The requested list key 'categories' could not be resolved as a collection/array/map/enumeration/iterator type. Example: people or people.{name} - [unknown location]

我只想从给定的 ArrayList<String> (List<String>) 填充 DropDownList，但它不起作用.如果我直接设置列表内容就可以了.

I just want the DropDownList to be populated from the given ArrayList<String> (List<String>), but it is not working. If I set the list content directly it works fine.

推荐答案

<s:select list = "categories" 
           key = "product.search.category" />

您正在列出 List<String> 并尝试通过 OGNL .(点表示法)访问不存在的字段.

You are listing a List<String> and trying to access, through OGNL . (dot notation), fields that do not exist.

在 OGNL 中

product.search.category

相当于Java

getProduct().getSearch().getCategory()

由于您要列出字符串，因此只需省略 key 属性，因为您的键和值都将是字符串本身.

Since you are listing Strings, just omit key attribute, because both your key and value will be the String itself.

您似乎也将 key 与 name 混淆了:key 是 的键code> 元素，而 name 是 Action 的属性，它将通过其 Setter 接收所选值.

It seems that you are confusing key with name too: key is the key of the <option> element, while name is the Action's attribute that will receive the chosen value through its Setter.

<s:select list = "categories" 
          name = "chosenCategory" />

<小时>

编辑:为了成功的生活，实施 Preparable Interface 并在那里加载你的静态"数据:

EDIT: for a succesful living, implement Preparable Interface and load there your "static" data:

public class ProductSearchAction extends ActionSupport implements Preparable {
    private List<String> categories;
    private String chosenCategory;

    @override
    public void prepare() throws Exception {      
        categories = new ArrayList<String>();
        categories.add("Eins");
        categories.add("Zwei");
        categories.add("Drei");
    }

    @Override
    public String execute() throws Exception {
        return SUCCESS;
    }

    /* GETTERS AND SETTERS */
}

而且你必须为 struts.xml 中的每个标签指定完全限定的类名...

And you must specify fully qualified class names for each tag in struts.xml...

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