java - Struts2:列表被超出其范围访问

Question

我有一个 struts2 Action 类，看起来像这样:

//import relevant packages

public class Product implements SessionAware, ServletRequestAware,
        ServletResponseAware, ServletContextAware {

    private String productName;
    private String description;
    private String price;

    private ServletContext servletContext; 
    private HttpServletRequest servletRequest; 
    private HttpServletResponse servletResponse; 
    private Map sessionMap;

    //getters and setters here

    public void setServletRequest(HttpServletRequest servletRequest) {
        this.servletRequest = servletRequest;
    }

    public void setSession(Map map) {
        this.sessionMap = map;
    }

    public void setServletResponse(HttpServletResponse servletResponse) {
        this.servletResponse = servletResponse;
    }

    public void setServletContext(ServletContext servletContext) {
        this.servletContext = servletContext;
    }

    public String execute() {


       //  do something here
        return "success";
    }

    public List<String> getCountries() {
        List<String> countries = new ArrayList<String>();
        countries.add("Australia");
        countries.add("Fiji");
        countries.add("New Zealand");
        countries.add("Vanuatu");
        return countries;
    }

}

sruts.xml 具有以下内容:

<?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="false" />
    <constant name="struts.devMode" value="true" />
    <package name="package.name" namespace="/" extends="struts-default">
        <action name="Product_input">
            <result>/jsp/Product.jsp</result>
        </action>
        <action name="Product_save" class="package.name.Product" method="execute">
            <result>/jsp/Details.jsp</result>
        </action>       
    </package>
</struts>

Product.jsp 由一个简单的表单组成:

<s:form action="Product_save">
        <s:textfield label="Product Name" key="productName"/>
        <s:textfield label="Description" key="description"/>
        <s:textfield label="Price" key="price"/>
        <s:submit/>
</s:form>

Details.jsp显示表单中输入的内容:

<h5>Details:</h5>
Product Name:
<s:property value="productName" />
<br /> Description:
<s:property value="description" />
<br /> Price: $
<s:property value="price" /> </br>
<s:property value="countries[0]" /> </br>

Details.jsp 中的最后一行尝试访问在操作类的 getCountries() 中声明的国家/地区列表，理想情况下它不应该打印任何内容，因为该方法从未被访问过，国家/地区列表也不是操作类属性的一部分(因此，在值堆栈中创建 Product 类型的对象时，它不应该有国家/地区)。

但是它确实会打印澳大利亚(列表的索引值)以及其他表单属性。这是如何/为何发生的？

Answer 1

当您在中写入国家时

countries[0]

它调用getCountries()方法。现在，您已将 [0] 放在其旁边，并将 countries 作为列表...

翻译成

getCountries().get(0)

您可以通过在 getCountries() 方法中放置 sysout 来验证这一点。