Question

我正在尝试创建一个仅在标记内可用的el变量，以便它类似于：

<mytaglib:mytag>
  Foo is ${foo}
</mytaglib:mytag>

我已经按照我可以找到的用于创建嵌套el变量的文档，但是，在mytag结束后可以使用$ {foo}。

缩小版的.tld文件是：

<?xml version="1.0" encoding="UTF-8" ?>

<taglib version="2.0" xmlns="http://java.sun.com/xml/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd">
  <description>My Tags</description>
  <tlib-version>1.0</tlib-version>
  <jsp-version>2.0</jsp-version>
  <short-name>mytaglib</short-name>
  <uri>http://www.example.com/taglibs/mytaglib</uri>

  <tag>
    <name>mytag</name>
    <tag-class>com.example.tags.MyTag</tag-class>
    <body-content>JSP</body-content>

    <variable>
      <name-given>used</name-given>
      <variable-class>java.lang.String</variable-class>
      <scope>NESTED</scope>
    </variable>
  </tag>
</taglib>

然后MyTag执行以下操作（我删除了所有不应该相关的代码）：

public class MyTag extends BodyTagSupport
{
  // these are subtags
  private JspFragment below;
  private JspFragment at;

  @Override
  public int doStartTag() throws JspException
  {
    return EVAL_BODY_BUFFERED;
  }

  @Override
  public int doEndTag() throws JspException
  {
    try
    {
      if (aBoolean)
      {
          below.invoke(pageContext.getOut());
      }
      else
      {
          at.invoke(pageContext.getOut());
      }
    }
    catch (IOException e)
    {
      throw new JspException(e);
    }

    return EVAL_PAGE;
  }

  @Override
  public void doInitBody() throws JspException
  {
    pageContext.setAttribute("used", "valueOfUsed");
  }

  @Override
  public int doAfterBody() throws JspException
  {
    try
    {
      bodyContent.writeOut(bodyContent.getEnclosingWriter());
    }
    catch (IOException e)
    {
      throw new JspException(e);
    }

    return SKIP_BODY;
  }
}

我的理解是doInitBody中的pageContext.setAttribute（）应该在嵌套范围内，并且你在doAfterBody中评估实际的主体。这似乎应该是这种情况，因为'used'在标签范围之外可用。

一般背景...标签看起来像（简化形式）

<mytaglib:mytag>
  Used is ${used}
</mytaglib:mytag>

或

<mytaglib:mytag>
  <mytaglib:at>
    You are at your limit, you have used: ${used}
  </mytaglib:at>
  <mytaglib:below>
    You are below your limit, you have used: ${used}
  </mytaglib:below>
</mytaglib:mytag>

如何将$ {used}限定为mytag？

Answer 1

我总是将JSTL作为我写的任何标签的模型。因此，我的方法是查看执行类似操作的标记的源代码，然后复制它。＆lt; c：forEach＆gt;标签是一个很好的例子。

JSTL中的LoopTagSupport类实现接口 javax.servlet.jsp.tagext.TryCatchFinally ，在doFinally方法中，它手动调用pageContext.removeAttribute（）。

引用JSTL1.1源代码分发：

/**
 * Removes any attributes that this LoopTagSupport set.
 *
 * <p> These attributes are intended to support scripting variables with
 * NESTED scope, so we don't want to pollute attribute space by leaving
 * them lying around.
 */
public void doFinally() {
    /*
     * Make sure to un-expose variables, restoring them to their
     * prior values, if applicable.
     */
    unExposeVariables();
}

/**
 * Removes page attributes that we have exposed and, if applicable,
 * restores them to their prior values (and scopes).
 */
private void unExposeVariables() {
    // "nested" variables are now simply removed
if (itemId != null)
        pageContext.removeAttribute(itemId, PageContext.PAGE_SCOPE);
if (statusId != null)
    pageContext.removeAttribute(statusId, PageContext.PAGE_SCOPE);
}

jsp taglibs的嵌套el变量

1 个答案: