How does the namespace attribute in a Struts2 package work?

Question

I am still confused how to properly use the namespace attribute in Struts2.

In the namespace configuration, it was mentioned that:

Namespaces are not a path!

Namespace are not hierarchical like a file system path. There is one namespace level. For example if the URL /barspace/myspace/bar.action is requested, the framework will first look for namespace /barspace/myspace. If the action does not exist at /barspace/myspace, the search will immediately fall back to the default namespace "". The framework will not parse the namespace into a series of "folders". In the Namespace Example, the bar action in the default namespace would be selected.

I have tried making a simple Struts2 sample:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN" 
                        "http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
    <constant name="struts.devMode" value="true" />

    <package name="default" extends="struts-default">
        <action name="defaultIndex">
            <result name="success">/pages/default.jsp</result>
        </action>
    </package>

    <package name="package1" namespace="/" extends="struts-default">
        <action name="index1">
            <result name="success">/pages/home1.jsp</result>
        </action>
    </package>

    <package name="package2" namespace="/namespace1" extends="struts-default">
        <action name="index2">
            <result name="success">/pages/home2.jsp</result>
        </action>   
    </package>

    <package name="package3" namespace="/namespace1/namespace2" extends="struts-default">
        <action name="index3">
            <result name="success">/pages/home3.jsp</result>
        </action>
    </package>
</struts>

Where SampleDynamicWebProject is the context root.

Based on the documentation, if I try

.../SampleDynamicWebProject/randomText/defaultIndex

Then, Struts2 will look for the /randomText namespace and check for the defaultIndex action. If it doesn't exist, then it will look for the default namespace which is the package with no namespace attribute.

But if I try this URL:

.../SampleDynamicWebProject/namespace1/randomText/index2

Struts2 should look at the /namespace1/randomText namespace for the index2 action and if it cannot see one, then it should look at the default namespace. However, the URL above is still directed at the index2 action in the /namespace1.

The same thing is happening when I try

.../SampleDynamicWebProject/randomText/index1

The index1 in the root namespace is invoked.

Can you please clarify how exactly it works?

Answer 1

You're definitely right, nowhere in the documentation is mentioned that if a namespace is part of the URL, it is enough to make the whole thing work.

But it does, and here is how it works in detail:

To parse an URL and call the appropriate namespace and action, Struts2 uses an ActionMapper:

The ActionMapper interface provides a mapping between HTTP requests and action invocation requests and vice-versa.

There are different implementations, but the default one is the DefaultActionMapper.

When an URL is analyzed, the parseNameAndNamespace() method is invoked. If it's not the default "" nor the root "/" one, and the alwaysSelectFullNamespace attribute is set to false (that is the default), then the available namespaces are scanned:

The magic is in this line:

if (ns != null 
 && prefix.startsWith(ns) 
 && (prefix.length() ==ns.length() || prefix.charAt(ns.length()) == '/')) {
    if (ns.length() > namespace.length()) {
        namespace = ns;
    }
   ///... 
}

name = uri.substring(namespace.length() + 1);

In your example:

/namespace1/randomText/index2

prefix = /namespace1/randomText/
ns     = /namespace1

In your case it is not null, the URI starts with the namespace, the length is not the same BUT the character after the /namespace1 String in the URI is a slash, then the action mapper decides that:

namespace = /namespace1
action    = randomText/index2

This is why the namespace is taken. But then why it works, since the action name is index2 and not randomText/index2 ?

The second magic is in this other line:

if (!allowSlashesInActionNames) {
    int pos = name.lastIndexOf('/');
    if (pos > -1 && pos < name.length() - 1) {
        name = name.substring(pos + 1);
    }
}

If the allowSlashesInActionNames attribute is set to false (that is the default) and the action contains slashes (like in randomText/index2), then strips everything up to the last slash, transforming randomText/index2 in index2.

Then as long as you have an URI that is starting with a namespace and ending with an action, no matter what's in the middle, it works.

It should not work instead using /randomText/namespace1/index2, because no namespace is starting with /randomText.