DDevelopment & Design

Virgo Snaps with Apache Tiles integration

After smoke tests become time to try using Virgo Snaps in more practical way. In modular application it will be useful to run it with templating framework. According to animal-menu-bar sample it will be better if developer of snap will not know anything about layout of host application and snippets like:

<jsp:include page="/../top.jsp"/>
(...)
<jsp:include page="/../bottom.jsp"/>

will be not necessary to put in snap pages. So lets modify a bit hosts jsps. Template page could look similar to old index.jsp:

<%@ taglib prefix="tiles" uri="http://tiles.apache.org/tags-tiles" %>
<jsp:include page="top.jsp"/>

<tiles:insertAttribute name="body" />

<jsp:include page="bottom.jsp"/>

Now index.jsp should not have includes:

 <p>
 The Snap Menu Bar sample is intended to showcase the ability to dynamically change the content of a menu bar using snaps. Each
 of the snaps that might be displayed in the menu bar includes a top and bottom JSP page and inherits it's styling from the host
 bundle.  Therefore, the snap bundle is only responsible for showing a small subset of content.
 </p>

Template definition should have one template without any attributes (it will be added dynamicly):

<tiles-definitions>
    <definition name="defaultTemplate" template="/template.jsp">
    </definition>
</tiles-definitions>

To dynamic adding this definitions we must implement our TilesView. I’ve used one which is a part of parancoe – Open Source Java Web Framework available on Google Code: http://code.google.com/p/parancoe/source/browse/plugins/parancoe-plugin-tiles/src/main/java/org/parancoe/plugin/tiles/CheapTilesView.java?r=f42be9c3c8e2df436d4970cfdaea1aff73d9cfdb and modify it a bit for our purposes. Most interesting part is:

    protected void renderMergedOutputModel(Map model, HttpServletRequest request,
            HttpServletResponse response)
            throws Exception {

        try {
            super.renderMergedOutputModel(model, request, response);
        } catch (TilesException te) {
            lazyRegisterThanRender(request, response);
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    private void lazyRegisterThanRender(HttpServletRequest request, HttpServletResponse response) throws IllegalStateException {
        ServletContext servletContext = getServletContext();
        MutableTilesContainer container = (MutableTilesContainer)
                ServletUtil.getContainer(servletContext);;
        Definition definition = new Definition();

        String[] arr = parsePath(getUrl());
        String subContextPart = arr[0];
        String mainUrlPart    = arr[1];

        definition.setName(getUrl());
        definition.setExtends((String) getAttribute(KEY_DEFAULT_TEMPLATE,
                DEFAULT_DEFAULT_TEMPLATE));
        String attributeList = (String) getAttribute(KEY_DEFAULT_ATTRIBUTES,
                DEFAULT_DEFAULT_ATTRIBUTES);

        String[] attributes = attributeList.split(",");
        if (attributes.length == 1) {
            addAttributeWithPathValueToDefinition(attributes[0], subContextPart, mainUrlPart, definition);
        } else {
            for (String attribute : attributes) {
                addAttributeWithPathValueToDefinition(attributes[0], subContextPart, mainUrlPart + "_" + attribute, definition);
            }
        }

        container.register(definition, request, response);
        container.render(getUrl(), new Object[]{request, response});
    }

How can we see here, lazyRegisterThanRender will be invoked if Tiles will have problems in our case in resolving view name. This method registering new template which extends default one. It also adds attributes taking its values from view name. parsePath parsing path in form: view@snap or only: view:

private String[] parsePath(String path) {
        String[] arr = new String[] {"", ""};
        int indexOfAt = path.indexOf('@');
        if (indexOfAt > 0) {
            arr[0] = '/' + path.substring(indexOfAt+1, path.length());
            arr[1] = path.substring(0, indexOfAt);
        } else {
            arr[1] = path;
        }
        return arr;
    }

In our case will be only body attribute.

To use Tiles we should define tilesConfigurer in spring context. But before this we must declare DispatcherServlet in web.xml which will past requests to our controllers in web.xml:

<servlet>
    <servlet-name>snap</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>2</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>snap</servlet-name>
    <url-pattern>/*</url-pattern>
</servlet-mapping>

After this simply adding WEB-INF/snap-servlet.xml context of application will be read:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="
      http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
      http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
          http://www.springframework.org/schema/osgi http://www.springframework.org/schema/osgi/spring-osgi.xsd"
        default-autowire="byName">

    <bean id="tilesConfigurer" class="org.springframework.web.servlet.view.tiles2.TilesConfigurer">
        <property name="definitions">
            <list>
                <value>/WEB-INF/tiles.xml</value>
            </list>
        </property>
        <property name="useMutableTilesContainer" value="true"/>
    </bean>

    <bean id="tilesViewResolver" class="org.springframework.web.servlet.view.tiles2.TilesViewResolver">
        <property name="attributesMap">
            <map>
                <entry key="CheapTilesView.DEFAULT_TEMPLATE" value="defaultTemplate"/>
                <entry key="CheapTilesView.DEFAULT_ATTRIBUTES" value="body"/>
            </map>
        </property>
        <property name="viewClass" value="CheapTilesView"/>
    </bean>

    <bean class="MainController"/>

</beans>

After this, we must to add templates definitions: lib/tiles-jsp.tld and few entries in template.mf:

Manifest-Version: 1
Bundle-SymbolicName: animal.menu.bar
Bundle-Version: 1.0
Bundle-ManifestVersion: 2
Bundle-Name: Multiple Styles Host
Web-ContextPath: /animal-menu-bar
Import-Library:
 org.springframework.spring;version="[3.0,3.1)"
Import-Bundle:
 com.springsource.org.apache.taglibs.standard;version="[1.1.2,1.3)",
 com.springsource.javax.servlet.jsp.jstl;version="[1.1.2, 1.1.3)",
 org.eclipse.virgo.snaps.api;version="[1.0,2.0)",
 com.springsource.org.apache.tiles;version="2.1.3",
 org.apache.tiles.core;version="2.1.3",
 org.apache.tiles.servlet;version="2.1.3",
 org.apache.tiles.jsp;version="2.1.3"
Import-Package:
 org.eclipse.virgo.snaps.core;version="[1.0,2.0)",
 javax.servlet;version="2.5",
 javax.servlet.http;version="2.5",
 javax.servlet.jsp;version="2.1",
 org.tuckey.web.filters.urlrewrite;version="[3.1.0,3.1.0]",
 org.springframework.js.resource;version="[2.0,2.1)",
 org.springframework.stereotype;version="[3.0,3.1)",
 org.springframework.web.bind.annotation;version="[3.0,3.1)",
 org.springframework.web.servlet;version="[3.0,3.1)",
 org.springframework.web.servlet.view.tiles2;version="[3.0,3.1)",
 org.apache.tiles;version="2.1.3",
 org.apache.tiles.context;version="2.1.3",
 org.apache.tiles.impl;version="2.1.3",
 org.apache.tiles.jsp.context;version="2.1.3",
 org.apache.tiles.mgmt;version="2.1.3",
 org.apache.tiles.renderer.impl;version="2.1.3",
 org.apache.tiles.servlet.context;version="2.1.3"

Our MainController will look like:

@Controller
public class MainController {
    @RequestMapping("/")
    public String rootHandler() {
        return "index";
    }
    @RequestMapping("/index.htm")
    public String snapHandler(@RequestParam("snap") String snap) {
        return "index@" + snap;
    }
}

So we must change top.jsp in host application:

                <snaps:snaps var="snaps">
                    <c:forEach var="snap" items="${snaps}">
                        <li><a href="<c:url value="index.htm?snap=${snap.properties['link.path']}"/>">
                            ${snap.properties['link.text']}</a>
                        </li>
                    </c:forEach>
                </snaps:snaps>

And also in snap.properties of both snaps link.path so it should be equals to snap subcontext (e.g. cat, dog).

After all of this we will have some troubles with resources handling so will be necessary to add urlrewrite filters like it was writed on Rob’s blog about Spring Slices – precursor of Snaps:

Our repository/usr should have:

commons-beanutils-1.8.0.jar
commons-digester-1.8.1.jar
com.springsource.org.apache.commons.collections-3.2.1.jar
com.springsource.org.apache.tiles-2.1.3.jar
com.springsource.org.tuckey.web.filters.urlrewrite-3.1.0.jar
org.eclipse.virgo.snaps.api.jar
org.eclipse.virgo.snaps.core.jar
tiles-core-2.1.3.jar
tiles-jsp-2.1.3.jar
tiles-servlet-2.1.3.jar

which we can copy from maven repository.

Patch with these changes is available on github

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Private fields and methods are not private in groovy

I used to code in Java before I met groovy. Like most of you, groovy attracted me with many enhancements. This was to my surprise to discover that method visibility in groovy is handled different than Java!

Consider this example:

class Person {
private String name
public  String surname

private Person() {}

private String signature() { "${name?.substring(0, 1)}. $surname" }

public String toString() { "I am $name $surname" }
}

How is this class interpreted with Java?

  1. Person has private constructor that cannot be accessed
  2. Field "name" is private and cannot be accessed
  3. Method signature() is private and cannot be accessed

Let's see how groovy interpretes Person:

public static void main(String[] args) {
def person = new Person()   // constructor is private - compilation error in Java
println(person.toString())

    person.@name = 'Mike'       // access name field directly - compilation error in Java
println(person.toString())

    person.name = 'John'        // there is a setter generated by groovy
println(person.toString())

    person.@surname = 'Foo'     // access surname field directly
println(person.toString())

    person.surname = 'Bar'      // access auto-generated setter
println(person.toString())

println(person.signature()) // call private method - compilation error in Java
}

I was really astonished by its output:

I am null null
I am Mike null
I am John null
I am John Foo
I am John Bar
J. Bar

As you can see, groovy does not follow visibility directives at all! It treats them as non-existing. Code compiles and executes fine. It's contrary to Java. In Java this code has several errors, pointed out in comments.

I've searched a bit on this topic and it seems that this behaviour is known since version 1.1 and there is a bug report on that: http://jira.codehaus.org/browse/GROOVY-1875. It is not resolved even with groovy 2 release. As Tim Yates mentioned in this Stackoverflow question: "It's not clear if it is a bug or by design". Groovy treats visibility keywords as a hint for a programmer.

I need to keep that lesson in mind next time I want to make some field or method private!

DDevelopment & Design

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