1 Table of Contents
2 PROBLEM: Universal Button Solutions: ------------------------------ PROBLEM
SOLUTIONS: DispatchUtil, (new) DispatchAction, ButtonTagUtil
3 Uses
3.1 Action Class Code
3.2 Mulitiple Image Tags
3.3 Link Tags
3.4 Submit Tags
3.5 File Browse Tags
3.6 Button Tags
3.7 struts-config.xml Uses
3.7.1 MappingDispatchAction
3.7.2 LookupDispatchAction
4 SOLUTION ONE: DispatchUtil Code ----------------------------------- SOLUTION ONE
5 (new) DispatchAction
5.1 Discussion
5.2 SOLUTION TWO: (new) DispatchAction Code --------------------------- SOLUTION TWO
6 POAO (plain old action object or even non-struts): Solution
6.1 Discussion
6.2 SOLUTION THREE: ButtonTagUtil Code -------------------------------- SOLUTION THREE
7 Links
8 Comments (Peanut Gallery)
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There is a persistent problem in web applications in handling multiple buttons, and this is especially a problem when the buttons are images.
Struts has provided a solution for this with DispatchAction and its progeny. I have found this solution to be too heavy, too complicated, and too obtuse. So, I have engendered my own.
The principle reason for this class is the problem with <input type='image' name='whatever'> tags in HTML. Those tag send the values in the name attribute as whatever.x=9 and whatever.y=26. DispatchAction and its progeny provide a melange of solutions but no common way to deal with <a href='whatever.do'>, <input type='submit'>, <input type='image'>, <input type='file'>, or whatever. This class, DispatchUtil does that. If you prefer to use a subclass, just provide the functionality in this class in a class extending Action. Herbert Rabago came up with the idea of providing the functionality in a utility class and I really like that idea. So, here we go.
N.B. the uses of "dispatch". If you do not like using "dispatch", then you can rewrite the code in the getMethodName(...) method. Essentially, you will need to replace ".dispatch" with something else in the tag names which you can identify in the enumeration. You have to use a suffix with this logic. But, if you want a prefix, e.g. "dispatch.update" or "method.update", then you will have to change the logic too. Suffix logic seems to best fit the existing methods in String. Otherwise, I would have used a prefix. You may want to anyway.
In all the following tag uses, you use the Action class code in execute(...) or process(...) as given directly below.
ActionForward = forward = new DispatchUtil().dispatch(this,mapping,form,request,response); |
Multiple image tags are the primary reason for this class. Integrating this into a common solution is the difficulty.
<input type='image' name='update.dispatch' src='update.gif'> <input type='image' name='delete.dispatch' src='delete.gif'> |
<a href='profile.do?update.dispatch=whatever'> <a href='profile.do?delete.dispatch=whatever'> |
<input type='submit' name='update.dispatch' value='whatever'> <input type='submit' name='delete.dispatch' value='whatever'> |
<input type='file' name='update.dispatch'> <input type='file' name='delete.dispatch'> |
<input type='button' name='update.dispatch' value='whatever'> <input type='button' name='delete.dispatch' value='whatever'> |
If you like to do things the way they are done with DispatchActions and use Struts xml for commands, then the following are possibilities. Please note that you never have to do this. Struts xml configuration is wholly voluntary for this solution. If you want the sort of behavior you get with MappingDispatchAction using DispatchUtil, then you do as we indicate. This does not mean, of course, that you have to use MappingDispatchAction. DispatchUtil completely absorbs all the functionality of the DispatchActions. You will see, further, that no struts-config.xml configuration is required at all for LookupDispatchActions.
This solution depends not on the value of the name attributes in the html tags, but strictly on the value of the path attributes in the html tags, anytime /updateProfile.do is called in the example below, any name attributes will be overridden and the value of the ActionMapping property called "parameter" will be operative instead.
{{{<action path="/updateProfile"
type="org.example.ProfileAction"
parameter="update.dispatch"
name="profileForm"
validate="true"
input="/editProfile.jsp"
scope="request">
<forward name="success" path="/updatedProfile.jsp"/>
</action>
<action path="/deleteSubscription"
type="org.example.ProfileAction"
name="profileForm"
scope="request"
input="/subscription.jsp"
parameter="delete.dispatch">
<forward name="success" path="/deletedSubscription.jsp"/>
</action>
}}}
This solution depends not on the value of the path attribute or the parameter property in the ActionMapping, notice that no parameter attribute exists below, but strictly on the values of the name attributes as indicated in our section on the tags. In other words, we don't have to configure struts-config.xml for what used to be LookupDispatchActions.
<action path="/updateProfile"
type="org.example.ProfileAction"
name="profileForm"
validate="true"
input="/editProfile.jsp"
scope="request">
<forward name="success" path="/updatedProfile.jsp"/>
</action>
<action path="/deleteSubscription"
type="org.example.ProfileAction"
name="profileForm"
scope="request"
input="/subscription.jsp"
<forward name="success" path="/deletedSubscription.jsp"/>
</action>
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package com.crackwillow.struts.util.dispatch;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Enumeration;
import java.util.HashMap;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.util.MessageResources;
public class DispatchUtil {
protected static Log log = LogFactory.getLog(DispatchUtil.class);
protected static MessageResources messages = MessageResources.getMessageResources ("org.apache.struts.actions.LocalStrings");
protected HashMap methods = new HashMap();
protected Class [] types = { ActionMapping.class,
ActionForm.class,
HttpServletRequest.class,
HttpServletResponse.class };
public ActionForward dispatch(Action action,
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws Exception {
String methodName = getMethodName(request,mapping);
Class clazz = action.getClass();
if ("execute".equals(methodName) || "perform".equals(methodName)){
// Prevent recursive calls
String message = messages.getMessage("dispatch.recursive", mapping.getPath());
log.error(message);
throw new ServletException(message);
}
return dispatchMethod(action,clazz,mapping, form, request, response, methodName);
}
protected ActionForward dispatchMethod(Action action,
Class clazz,
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response,
String name)
throws Exception {
if (name == null) {
return this.unspecified(mapping, form, request, response);
}
Method method = null;
try {
method = getMethod(clazz,name);
} catch(NoSuchMethodException nsme) {
String message = messages.getMessage("dispatch.method", mapping.getPath(), name);
log.error(message, nsme);
throw nsme;
}
ActionForward forward = null;
try {
Object args[] = { mapping, form, request, response };
forward = (ActionForward)method.invoke(action, args);
} catch(ClassCastException cce) {
String message = messages.getMessage("dispatch.return", mapping.getPath(), name);
log.error(message, cce);
throw cce;
} catch(IllegalAccessException iae) {
String message = messages.getMessage("dispatch.error", mapping.getPath(), name);
log.error(message, iae);
throw iae;
} catch(InvocationTargetException ite) {
Throwable t = ite.getTargetException();
if (t instanceof Exception) {
throw ((Exception) t);
} else {
String message = messages.getMessage("dispatch.error", mapping.getPath(), name);
log.error(message, ite);
throw new ServletException(t);
}
}
return (forward);
}
protected static String getMethodName(HttpServletRequest request, ActionMapping mapping) {
String methodName = null;
String buttonValue = null;
String paramProperty = mapping.getParameter();
if((paramProperty != null)) {
methodName = paramProperty.substring(0,paramProperty.indexOf('.'));
} else {
Enumeration enum = request.getParameterNames();
while(enum.hasMoreElements()) {
buttonValue = (String)enum.nextElement();
StdOut.log("log.dispatch","DispatchUtil buttonValue = " + buttonValue);
if(buttonValue.indexOf(".dispatch") >= 0) {
methodName = buttonValue;
break;
}
}
}
return methodName.substring(0,methodName.indexOf('.'));
}
protected Method getMethod(Class clazz,String name)
throws NoSuchMethodException {
synchronized(methods) {
Method method = (Method) methods.get(name);
if (method == null) {
method = clazz.getMethod(name, types);
methods.put(name, method);
}
return (method);
}
}
protected ActionForward unspecified(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws Exception {
String message = messages.getMessage( "dispatch.parameter", mapping.getPath(), getMethodName(request,mapping));
log.error(message);
throw new ServletException(message);
}
}
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If, rather than having a utility class provide the functionality, you prefer an Action class. Here is a redoing of the DispatchAction class to let you do that. You use this class for ALL the progeny of DispatchAction class, i.e. this class replaces completely DispatchAction, LookupDispatchAction, and MappingDispatchAction. You can alter this class to get whatever subsidiary functionality you might want and which some might consider essential.
package com.crackwillow.struts.action;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Enumeration;
import java.util.HashMap;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.util.MessageResources;
public abstract class DispatchAction
extends Action {
protected Class clazz = this.getClass();
protected static Log log = LogFactory.getLog(SimpleDispatchAction.class);
protected static MessageResources messages = MessageResources.getMessageResources ("org.apache.struts.actions.LocalStrings");
protected HashMap methods = new HashMap();
protected Class[] types = { ActionMapping.class,
ActionForm.class,
HttpServletRequest.class,
HttpServletResponse.class };
public ActionForward execute(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws Exception {
String name = getMethodName(request,mapping);
if ("execute".equals(name) || "perform".equals(name)){
// Prevent recursive calls
String message = messages.getMessage("dispatch.recursive", mapping.getPath());
log.error(message);
throw new ServletException(message);
}
return dispatchMethod(mapping, form, request, response, name);
}
protected ActionForward dispatchMethod(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response,
String name)
throws Exception {
if (name == null) {
return this.unspecified(mapping, form, request, response);
}
Method method = null;
try {
method = getMethod(name);
} catch(NoSuchMethodException nsme) {
String message = messages.getMessage("dispatch.method", mapping.getPath(), name);
log.error(message, nsme);
throw nsme;
}
ActionForward forward = null;
try {
Object args[] = {mapping, form, request, response};
forward = (ActionForward) method.invoke(this, args);
} catch(ClassCastException cce) {
String message = messages.getMessage("dispatch.return", mapping.getPath(), name);
log.error(message, cce);
throw cce;
} catch(IllegalAccessException iae) {
String message = messages.getMessage("dispatch.error", mapping.getPath(), name);
log.error(message, iae);
throw iae;
} catch(InvocationTargetException ite) {
Throwable t = ite.getTargetException();
if (t instanceof Exception) {
throw ((Exception) t);
} else {
String message = messages.getMessage("dispatch.error", mapping.getPath(), name);
log.error(message, ite);
throw new ServletException(t);
}
}
return (forward);
}
protected static String getMethodName(HttpServletRequest request, ActionMapping mapping) {
String methodName = null;
String buttonValue = null;
String paramProperty = mapping.getParameter();
if((paramProperty != null)) {
methodName = paramProperty.substring(0,paramProperty.indexOf('.'));
} else {
Enumeration enum = request.getParameterNames();
while(enum.hasMoreElements()) {
buttonValue = (String)enum.nextElement();
StdOut.log("log.dispatch","DispatchUtil buttonValue = " + buttonValue);
if(buttonValue.indexOf(".dispatch") >= 0) {
methodName = buttonValue;
break;
}
}
}
return methodName.substring(0,methodName.indexOf('.'));
}
protected Method getMethod(String name)
throws NoSuchMethodException {
synchronized(methods) {
Method method = (Method) methods.get(name);
if (method == null) {
method = clazz.getMethod(name, types);
methods.put(name, method);
}
return (method);
}
}
protected ActionForward unspecified(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws Exception {
String message = messages.getMessage( "dispatch.parameter", mapping.getPath(), getMethodName(request,mapping));
log.error(message);
throw new ServletException(message);
}
protected ActionForward cancelled(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws Exception {
return null;
}
}
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You can use the same strategy to determine what button tag has been clicked without employing Struts. The best way to do this, in my opinion, in the following solution.
public class ButtonTagUtil {
public static String getName(HttpServletRequest request) {
String methodName = null;
String buttonValue = null;
Enumeration enum = request.getParameterNames();
while(enum.hasMoreElements()) {
buttonValue = (String)enum.nextElement();
if(buttonValue.indexOf(".dispatch") >= 0) {
methodName = buttonValue;
break;
}
}
return methodName.substring(0,methodName.indexOf('.'));
}
}
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StrutsCatalogInstrumentableForms
StrutsCatalogHidingImagesAndOtherResourcesUnderWEBINF
If your comments are extensive, you might want to provide a link instead of adding to this already incredibly verbose presentation.