Custom tags: passing in maps or other datatypes that arent strings

problem:
I needed to pass a hashmap into a custom tag. This hashmap was to be created on the jsp page using jstl, and then passed into the tag as an attribute.
For some reason i was not able to find the solution with just one google query.

solution:
1. first, to create a hashmap on the jsp using jstl and add some stuff to it:
<br /><jsp:useBean id="something" class="java.util.HashMap"><br /> <c:set target="${something}" property="name1" value="value1"/><br /> <c:set target="${something}" property="name-2" value="blee"/><br /></jsp:useBean><br />

2. next, add another attribute to your tag in the tld file:
<br /><attribute><br /> <name>someName</name><br /> <required>false</required><br /> <rtexprvalue>true</rtexprvalue><br /> <type>java.util.Map</type><br /></attribute><br />

3. finally, pass the hashmap into your tag .. <tag someName="${something}" /> and make sure that the setter in the tag takes in a Map

Path does not start with a "/" character

Problem:
I get this error when using the tiles plugin when building out some tiles:

java.lang.IllegalArgumentException: Path .some.tiles.path does not start with a "/" character

first, lets pretend that the tile in question looks like this:
<definition name=".some.tiles.path" extends=".some.other.tiles.path"> ..some stuff.. </definition>

Solution:
ive noticed that the reason for this error can be one of the following:

1. if you look at the tile that this tile extends, and what that tile extends, until you find the tile that extends nothing, that tile should have a definition like this:
<definition name=".some.base.tile" path="/a/real/path/to/some/jsp/somejsp.jsp"> ..some stuff.. </definition>
the key thing, is that the path of the parent tile starts with a "/" character

2. if #1 is not your problem, then you might have a duplicate definition of the tile name which the error talks about.

3. Another thing that can happen is that your tiles path that you are referencing in struts-config.xml does not exist at all, because maybe you misspelled it, in which case that same error is thrown.

JSP syntax: empty checks, params, misc

This stuff is so elementary that i am always annoyed to forget it every time i dont use jsp for a few months.

1. Get params from the url request, ie http://dogself.com?param1=test&something=poop
<c:out value="param1 is: ${param.param1} something is:${param.something}"/>

also there is ${params} for getting lists, but i would need to read up on that

2. checking if a request attribute is null or empty:
<c:if test="${param.page != null && not empty param.page}">
<c:import url="${base_html_dir}${param.page}"></c:import>
</c:if>


3. setting variables:
<c:set var="thingToSet" value="${1+ 3}">
this by default has the scope of 'page', also can be 'session' defined by attribute 'scope'

ill add more as i go

Using EL in custom tags as attributes

Problem:
I was working on a custom tag and i needed to pass it a bean from a JSP page kind of like this:
<customtag var="${somebean.something.else}">
I realized that what i was getting inside my custom tag was a String, not my bean.

Solution:
You need to use the ExpressionEvaluator to evaluate the expression, and get the bean, here is the code i used in my SimpleTag: (i was getting a Date object by the way)

<br /><br />ExpressionEvaluator eval = getJspContext().getExpressionEvaluator();<br />Date date = null;<br />//dateVar this is the EL expression<br />try { //this thing here resolves the date expression into a java object!<br /> date = (Date)eval.evaluate(dateVar, Date.class, getJspContext().getVariableResolver(), new FunctionMapper(){<br />public Method resolveFunction(String arg0, String arg1) {<br /> return null; //i couldnt figure out how to get a FunctionMapper from somewhere...<br />}<br /> });<br />} catch (ELException e1) {<br /> throw new JspException(e1);<br />}<br />


Edit Aug 7, 2008:
It has come to my attention that in jsp 2.0 the EL expressions are evaluated before being passed to the custom tags, so you dont need to do any of this crap anymore.

JSP: custom tag to modify its body

This is a skeleton of what is needed to build a custom jsp tag which does something to its body. For example a tag could change the urls of all the links found in its body.

<br />package com.mycompany.package.of.the.tag;<br /><br />import javax.servlet.jsp.JspException;<br />import javax.servlet.jsp.JspWriter;<br />import javax.servlet.jsp.tagext.BodyContent;<br />import javax.servlet.jsp.tagext.BodyTagSupport;<br /><br />public class CustomTag extends BodyTagSupport {<br />private static final long serialVersionUID = 1L;<br /><br />public int doAfterBody() throws JspException {<br /> try {<br /> BodyContent bc = getBodyContent();<br /> String body = bc.getString();<br /> // do something to the body here.<br /> JspWriter out = bc.getEnclosingWriter();<br /> if(body != null) {<br /> out.print(buff.toString());<br /> }<br /> } catch(IOException ioe) {<br /> throw new JspException("Error: "+ioe.getMessage());<br /> }<br /> return EVAL_BODY_INCLUDE;<br /> }<br />}<br />

make a file called CustomTag.tld and put it into WEB-INF:
<br /><?xml version = "1.0" encoding = "ISO-8859-1" ?><br /><!DOCTYPE taglib<br />PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.1//EN"<br />"http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_1,dtd"><br /><taglib><br /><tlibversion>1.0</tlibversion><br /><jspversion>1.1</jspversion><br /><uri>com.mycompany.CustomTag</uri><br /><shortname>Custom Tag</shortname><br /><tag><br /><name>ct</name><br /><tagclass>com.mycompany.package.of.the.tag.CustomTag</tagclass><br /><bodycontent>JSP</bodycontent><br /></tag><br /></taglib><br /><br />

use it like this on your JSP:
<%@ taglib uri="com.mycompany.CustomTag" prefix="x"%>

<x:ct>
here is some stuff inside the tag!
<c:out value="${someparam}"/>
</x:ct>

How to make a redirect servlet

make a servlet which calls the following method on doPost() and on doGet()

<br />private void doRedirect(HttpServletRequest request, HttpServletResponse response) throws ServletException {<br /> String servletPath = request.getServletPath();<br /> //do something with the path<br /> String newServletPath = servletPath.toLowerCase();<br /> try {<br /> getServletContext().getRequestDispatcher(newServletPath).forward(request, response);<br /> } catch(IOException ioE) {<br /> throw new ServletException("Unable to forward request: " + servletPath + " to path: " + newServletPath, ioE);<br /> }<br />}<br />