自定义JSP标记 - 如何获取标记的主体？

Question

I have a custom jsp tag like this:

<a:customtag>
    The body of the custom tag...
    More lines of the body...
</a:customtag>

In the custom tag, how can I get the text of what the body is?

Answer 1

It's complicated because there are two mechanisms.

If you're extending SimpleTagSupport, you get getJspBody() method. It returns a JspFragment that you can invoke(Writer writer) to have the body content written to the writer.

You should use SimpleTagSupport unless you have a specific reason to use BodyTagSupport (like legacy tag support) as it is - well - simpler.

If you are using classic tags, you extend BodyTagSupport and so get access to a getBodyContent() method. That gets you a BodyContent object that you can retrieve the body content from.

Answer 2

If you are using a custom tag with jsp 2.0 approach, you can do it as:

make-h1.tag

<%@tag description="Make me H1 " pageEncoding="UTF-8"%>   
<h1><jsp:doBody/></h1>

Use it in JSP as:

<%@ taglib prefix="t" tagdir="/WEB-INF/tags"%>
<t:make-h1>An important head line </t:make-h1>

Answer 3

To expand on Brabster's answer , I've used SimpleTagSupport.getJspBody() to write the JspFragment to an internal StringWriter for inspection and manipulation:

public class CustomTag extends SimpleTagSupport {
    @Override public void doTag() throws JspException, IOException {
        final JspWriter jspWriter = getJspContext().getOut();
        final StringWriter stringWriter = new StringWriter();
        final StringBuffer bodyContent = new StringBuffer();

        // Execute the tag's body into an internal writer
        getJspBody().invoke(stringWriter);

        // (Do stuff with stringWriter..)

        bodyContent.append("<div class='custom-div'>");
        bodyContent.append(stringWriter.getBuffer());
        bodyContent.append("</div>");

        // Output to the JSP writer
        jspWriter.write(bodyContent.toString());
    }
}

}