JSP-自定义Taglib的问题

Question

I just tried to add a custom taglib to my project, such that the testtaglib.tld file contains:

<taglib>
<tlibversion>1.0</tlibversion>
  <jspversion>1.1</jspversion>
  <shortname>name</shortname>

    <tag>
        <name>test</name>
        <tagclass>taglib.TestTaglib</tagclass>
        <bodycontent>empty</bodycontent>
        <attribute>
            <name>testCode</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
            <type>java.lang.String</type>
        </attribute>
    </tag>
<taglib>

And then I added taglib class TestTaglib.java

public class TestTaglib extends TagSupport {

    private String  testCode;
    public int doStartTag() throws JspException {
        try {
            JspWriter out = pageContext.getOut();
            //doing some conversion with testCode
            out.print(testCode);
            return EVAL_PAGE;
        } catch(IOException ioe) {
            throw new JspException("Error: " + ioe.getMessage());
        }
    }
}

And then in .jsp file

<name:test testCode="${testCode}"/>

Okay the issue is: TestTaglib.java is recognizing values of testCode as ${testCode} and not the original value. Any suggestion?

Answer 1

Hi all inbuilt tag already handles the expression language. Just change your code as mentioned below and it will work fine.

 public class TestTaglib extends TagSupport {


 private String  testCode;
    public int doStartTag() throws JspException {
        try {
            JspWriter out = pageContext.getOut();
            //doing some conversion with testCode
            String value = (String) ExpressionUtil.evalNotNull("test", "testCode", testCode, String.class, this, pageContext);
            out.print(value);
            return EVAL_PAGE;
        } catch(IOException ioe) {
            throw new JspException("Error: " + ioe.getMessage());
        }
    }
}

ExpressionUtil is class provided under org.apache.taglibs.standard.tag.el.core package.

Here is short desc of evalNotNull method args

your tag name is test
to eval in your case it is testCode
which is el expression ${testCode}
Class of expression value whether it is Boolean,String or any Object
Reference of tag handler class so you can pass this
which is coming from TagSupport