为什么这个PrettyTime自定义标记在HTML输出中的“漂亮”日期之前产生11行空白文本？

Question

<%@ tag language="java" pageEncoding="utf-8" isELIgnored="false" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %>
<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>
<%@ tag import="com.ocpsoft.pretty.time.PrettyTime, java.util.Date"%>
<%@ attribute name="dateParam" required="true" type="java.util.Date" %>

<%
 PrettyTime p = new PrettyTime();
 String prettyDate = p.format(dateParam);
 jspContext.setAttribute("prettyDate", prettyDate.trim());
%>
<c:out value="${prettyDate}"/>

I can't figure out if I'm doing something wrong in this tag.

The PrettyTime library is supposed to just print a text version of a data, eg:

10 months ago

But I can't tell why this custom tag produces 11 lines of blank text before the "pretty" date in the HTML output?

Answer 1

Since Thorbjoern has already answered the cause, I'll only answer the solution since you'd likely to get rid of this annoyance.

You can configure your servletcontainer to trim whitespace left after processing the scriptlets and taglibs. In for example Apache Tomcat, you can do it by opening the /conf/web.xml , heading to the <servlet> definition of the JSP servlet, which look like follows on Tomcat 7

<servlet>
    <servlet-name>jsp</servlet-name>
    <servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class>
    <init-param>
        <param-name>fork</param-name>
        <param-value>false</param-value>
    </init-param>
    <init-param>
        <param-name>xpoweredBy</param-name>
        <param-value>false</param-value>
    </init-param>
    <load-on-startup>3</load-on-startup>
</servlet>

add an <init-param> of trimSpaces=true as follows to the <servlet> definition of JSP servlet:

    <init-param>
        <param-name>trimSpaces</param-name>
        <param-value>true</param-value>
    </init-param>

Restart Tomcat and this whitespace should be gone. At least, most of will be gone. You only need to take care that the whitespace which you've introduced yourself is physically removed from the JSP as well.

See also the JSP engine HOW-TO . Pretty all other servletcontainers have a similar configuration. Consult their documentation using the keyword "trim spaces".

---

As to the general approach, I'd suggest to transform that thing into a Java class and make an EL function of it instead. Death to the scriptlets .

<c:out value="${my:prettyTime(date)}" />

Answer 2

因为当您删除<％...％>时，仍然存在换行符，这些换行符会忠实地复制到生成的输出中。