Java 2 Ada

Atlas, the Ada Web Application demonstrator

By stephane.carrez 2012-05-22 21:12:41

AWA is a framework to build web applications on top of various robust components.

  • AWA uses Ada Server Faces for the web framework. This framework is using several patterns from the Java world such as Java Server Faces and Java Servlets.
  • AWA is architectured arround modules and plugins that allow to build, re-use and extend modules made of Ada code, Web pages or Javascript.
  • AWA provides a set of ready to use and extendable plugins that are common to many web application. This includes managing the login, authentication, users, permissions, a mail plugin, a blog plugin, a Javascript light editor.
  • AWA uses an Object Relational Mapping that helps in writing Ada applications on top of MySQL or SQLite databases. The ADO framework allows to map database objects into Ada records and access them easily.
  • AWA integrates a configurable event service which allows plugins to easily interact and connect with each other (either synchronously or asynchronously). The event service provided by AWA is heavily inspired from the Java Message Service.

To learn more on how to create easily a web application using AWA, look at the 4 minutes video.

The Atlas Web Application Demonstrator is a demonstration of an application using this AWA framework.

Ada Server Faces Application Example part 3: the action bean

By stephane.carrez 2011-05-02 21:01:32

In a previous article, I presented in the cylinder volume example the Ada Server Faces presentation layer and then the Ada beans that link the presentation and ASF components together. This article explains how to implement an action bean and have a procedure executed when a button is pressed.

Command buttons and method expression

We have seen in the presentation layer how to create a form and have a submit button. This submit button can be associated with an action that will be executed when the button is pressed. The EL expression is the mechanism by which we create a binding between the XHTML presentation page and the component implemented in Java or Ada. A method expression is a simple EL expression that represents a bean and a method to invoke on that bean. This method expression represent our action.

A typical use is on the h:commandButton component where we can specify an action to invoke when the button is pressed. This is written as:

<h:commandButton id='run' value='Compute'
       action="#{compute.run}"/>

The method expression #{compute.run} indicates to execute the method run of the bean identified by compute.

Method Bean Declaration

Java implements method expressions by using reflection. It is able to look at the methods implemented by an object and then invoke one of these method with some parameters. Since we cannot do this in Ada, some developer help is necessary.

For this an Ada bean that implements an action must implement the Method_Bean interface. If we take the Compute_Bean type defined in the Ada beans previous article, we just have to extend that interface and implement the Get_Method_Bindings function. This function will indicate the methods which are available for an EL expression and somehow how they can be called.

with Util.Beans.Methods;
...
   type Compute_Bean is new Util.Beans.Basic.Bean
          and Util.Beans.Methods.Method_Bean with record
      Height : My_Float := -1.0;
      Radius : My_Float := -1.0;
      Volume: My_Float := -1.0;
   end record;
   --  This bean provides some methods that can be used in a Method_Expression
   overriding
   function Get_Method_Bindings (From : in Compute_Bean)
      return Util.Beans.Methods.Method_Binding_Array_Access;

Our Ada type can now define a method that can be invoked through a method expression. The action bean always receives the bean object as an in out first parameter and it must return the action outcome as an Unbounded_String also as in out.

 procedure Run (From    : in out Compute_Bean;
                         Outcome : in out Unbounded_String);

Implement the action

The implementation of our action is quite simple. The Radius and Height parameters submitted in the form have been set on the bean before the action is called. We can use them to compute the cylinder volume.

procedure Run (From    : in out Compute_Bean;
                        Outcome : in out Unbounded_String) is
      V : My_Float;
   begin
      V := (From.Radius * From.Radius);
      V := V * From.Height;
      From.Volume := V * 3.141;
      Outcome := To_Unbounded_String ("compute");
   end Run;

Define the action binding

To be able to call the Run procedure from an EL method expression, we have to create a binding object. This binding object will hold the method name as well as a small procedure stub that will somehow tie the method expression to the procedure. This step is easily done by instantiating the ASF.Events.Actions.Action_Method.Bind package.

with ASF.Events.Actions;
...
   package Run_Binding is
     new ASF.Events.Actions.Action_Method.Bind
        (Bean  => Compute_Bean,
         Method => Run,
         Name    => "run");

Register and expose the action bindings

The last step is to implement the Get_Method_Bindings function. Basically it has to return an array of method bindings which indicate the methods provided by the Ada bean.

Binding_Array : aliased constant Util.Beans.Methods.Method_Binding_Array
  := (Run_Binding.Proxy'Unchecked_Access, Run_Binding.Proxy'Unchecked_Access);

overriding
function Get_Method_Bindings (From : in Compute_Bean)
   return Util.Beans.Methods.Method_Binding_Array_Access is
begin
   return Binding_Array'Unchecked_Access;
end Get_Method_Bindings;

What happens now?

When the user presses the Compute button, the brower will submit the form and the ASF framework will do the following:

  • It will check the validity of input parameters,
  • It will save the input parameters on the compute bean,
  • It will execute the method expression #{compute.run}:
  • It calls the Get_Method_Bindings function to get a list of valid method,
  • Having found the right binding, it calls the binding procedure
  • The binding procedure invokes the Run procedure on the object.

Next time...

We have seen the presentation layer, how to implement the Ada bean and this article explained how to implement an action that is called when a button is pressed. The next article will explain how to initialize and build the web application.

Ada Server Faces Application Example part 4: the server

By stephane.carrez 2011-04-18 20:35:58

In previous articles, we have seen that an Ada Server Faces application has a presentation layer composed of XHTML and CSS files. Similar to Java Server Faces, Ada Server Faces is a component-based model and we saw how to write the Ada beans used by the application. Later, we also learnt how an action bean can have a procedure executed when a button is pressed. Now, how can all these stuff fit together?

Well, to finish our cylinder volume example, we will see how to put everything together and get our running web application.

Application Initialization

An Ada Server Faces Application is represented by the Application type which holds all the information to process and dispatch requests. First, let's declare a variable that represents our application.

Note: for the purpose of this article, we will assume that every variable is declared at some package level scope. If those variables are declared in another scope, the Access attribute should be replaced by Unchecked_Access.

with ASF.Applications.Main;
...
   App : aliased ASF.Applications.Main.Application;

To initialize the application, we will also need some configuration properties and a factory object. The configuration properties are used to configure the various components used by ASF. The factory allows to customize some behavior of Ada Server Faces. For now, we will use the default factory.

with ASF.Applications;
...
   C        : ASF.Applications.Config;
   Factory : ASF.Applications.Main.Application_Factory;

The initialization requires to define some configuration properties. The VIEW_EXT property indicates the URI extension that are recognized by ASF to associate an XHTML file (the compute.html corresponds to the XHTML file compute.xhtml). The VIEW_DIR property defines the root directory where the XHTML files are stored.

C.Set (ASF.Applications.VIEW_EXT, ".html");
C.Set (ASF.Applications.VIEW_DIR, "samples/web");
C.Set ("web.dir", "samples/web");
App.Initialize (C, Factory);

Servlets

Ada Server Faces uses the Ada Servlet framework to receive and dispatch web requests. It provides a Faces_Servlet servlet which can be plugged in the servlet container. This servlet is the entry point for ASF to process incoming requests. We will also need a File_Servlet to process the static files. Note that these servlets are implemented using tagged records and you can easily override the entry points (Do_Get or Do_Post) to implement specific behaviors.

with ASF.Servlets.Faces;
with ASF.Servlets.Files;
...
   Faces : aliased ASF.Servlets.Faces.Faces_Servlet;
   Files   : aliased ASF.Servlets.Files.File_Servlet;

The servlet instances are registered in the application.

App.Add_Servlet (Name => "faces", Server => Faces'Access);
App.Add_Servlet (Name => "files", Server => Files'Access);

Once registered, we have to define a mapping that tells which URI path is mapped to the servlet.

App.Add_Mapping (Name => "faces", Pattern => "*.html");
App.Add_Mapping (Name => "files", Pattern => "*.css");

For the purpose of debugging, ASF provides a servlet filter that can be plugged in the request processing flow. The Dump_Filter will produce a dump of the request with the headers and parameters.

with ASF.Filters.Dump;
...
   Dump    : aliased ASF.Filters.Dump.Dump_Filter;

The filter instance is registered as follows:

App.Add_Filter (Name => "dump", Filter => Dump'Access);

And a mapping is defined to tell which URL will trigger the filter.

App.Add_Filter_Mapping (Name => "dump", Pattern => "*.html");

Application and Web Container

The application object that we created is similar to a Java Web Application packaged in a WAR file. It represents the application and it must be deployed in a Web Container. With Ada Server Faces this is almost the same, the application needs a Web container. By default, ASF provides a web container based on the excellent Ada Web Server implementation (other web containers could be provided in the future based on other web servers).

with ASF.Server.Web;
...
   WS : ASF.Server.Web.AWS_Container;

To register the application, we indicate the URI context path to which the application is associated. Several applications can be registered, each of them having a unique URI context path.

CONTEXT_PATH : constant String := "/volume";
...
WS.Register_Application (CONTEXT_PATH, App'Access);

Global Objects

An application can provide some global objects which will be available during the request processing through the EL expression. First, we will expose the application context path which allows to write links in the XHTML page that match the URI used for registering the application in the web container.

App.Set_Global ("contextPath", CONTEXT_PATH);

Below is an example of use of this contextPath variable:

<link media="screen" type="text/css" rel="stylesheet"
      href="#{contextPath}/themes/main.css"/>

Now, we will register the bean that we created for our application! This was explained in the Ada beans previous article.

with Volume;
...
   Bean    : aliased Volume.Compute_Bean;
...
   App.Set_Global ("compute", Util.Beans.Objects.To_Object (Bean'Access));

Note: For the purpose of this example, the Compute_Bean is registered as a global object. This means that it will be shared by every request. A future article will explain how to get a session or a request bean as in Java Server Faces.

Starting the server

Once the application is registered, we can start our server. Note that since Ada Web Server starts several threads that listen to requests, the Start procedure does not block and returns as soon as the server is started. The delay is necessary to let the server wait for requests during some time.

WS.Start;
delay 1000.0;

What happens to a request?

Let's say the server receives a HTTP GET request on /volume/compute.html. Here is what happens:

Volume ASF Flow

  • Ada Web Server receives the HTTP request
  • It identifies the application that matches /volume (our context path) and gives the control to it
  • The application identifies the servlet that processes the remaining URI, which is compute.html
  • It gives the control to the Dump_Filter filter and then to the Faces_Servlet servlet,
  • The faces servlet identifies the XHTML facelet file and reads the compute.xhtml file
  • ASF builds the component tree that describes the page and invokes the render response phase
  • While rendering, the EL expressions such as #{compute.radius} are evaluated and the value is obtained on our Bean global instance.
  • The HTML content is produced as part of the rendering process and returned by AWS.

References

asf_volume_server.adb

volume.ads

volume.adb

compute.xhtml

1 comments

Ada Server Faces Application Example part 2: the Ada beans

By stephane.carrez 2011-04-10 19:46:24

The first article explained how to design the presentation page of an Ada Server Faces application. This article presents the Ada beans that are behind the presentation page.

Ada Bean and presentation layer

We have seen that the presentation page contains components that make references to Ada beans with an EL expression.

<h:inputText id='height' size='10' value='#{compute.height}'>
        <f:converter converterId="float" />
</h:inputText>

The #{compute.height} is an EL expression that refers to the height property of the Ada bean identified as compute.

Writing the Cylinder Ada Bean

The Ada bean is a instance of an Ada tagged record that must implement a getter and a setter operation. These operations are invoked through an EL expression. Basically the getter is called when the view is rendered and the setter is called when the form is submitted and validated. The Bean interface defines the two operations that must be implemented by the Ada type:

with Util.Beans.Basic;
with Util.Beans.Objects;
...
   type Compute_Bean is new Util.Beans.Basic.Bean with record
      Height : My_Float := -1.0;
      Radius : My_Float := -1.0;
   end record;

   --  Get the value identified by the name.
   overriding
   function Get_Value (From : Compute_Bean;
                       Name : String) return Util.Beans.Objects.Object;

   --  Set the value identified by the name.
   overriding
   procedure Set_Value (From  : in out Compute_Bean;
                        Name  : in String;
                        Value : in Util.Beans.Objects.Object);

The getter and setter will identify the property to get or set through a name. The value is represented by an Object type that can hold several data types (boolean, integer, floats, strings, dates, ...). The getter looks for the name and returns the corresponding value in an Object record. Several To_Object functions helps in creating the result value.

   function Get_Value (From : Compute_Bean;
                       Name : String) return Util.Beans.Objects.Object is
   begin
      if Name = "radius" and From.Radius >= 0.0 then
         return Util.Beans.Objects.To_Object (Float (From.Radius));

      elsif Name = "height" and From.Height >= 0.0 then
         return Util.Beans.Objects.To_Object (Float (From.Height));

      else
         return Util.Beans.Objects.Null_Object;
      end if;
   end Get_Value;

The setter is similar.

   procedure Set_Value (From  : in out Compute_Bean;
                        Name  : in String;
                        Value : in Util.Beans.Objects.Object) is
   begin
      if Name = "radius" then
         From.Radius := My_Float (Util.Beans.Objects.To_Float (Value));
      elsif Name = "height" then
         From.Height := My_Float (Util.Beans.Objects.To_Float (Value));
      end if;
   end Set_Value;

Register the Cylinder Ada Bean

The next step is to register the cylinder bean and associate it with the compute name. There are several ways to do that but for the purpose of this example, there will be a global instance of the bean. That instance must be aliased so that we can use the Access attributes.

 Bean  : aliased Compute_Bean;

The Ada bean is registered on the application object by using the Set_Global procedure. This creates a global binding between a name and an Object record. In our case, the object will hold a reference to the Ada bean.

App : aliased ASF.Applications.Main.Application;
...
   App.Set_Global ("compute", Util.Beans.Objects.To_Object (Bean'Unchecked_Access));

Next Time...

We have seen how the presentation layer and the Ada beans are associated. The next article will present the action binding that links the form submission action to an Ada bean method.

Ada Server Faces Application Example part 1: the presentation

By stephane.carrez 2011-03-21 21:25:30

Ada Server Faces is a framework which allows to write and build web applications. This article presents through a simple example how to use ASF to write a simple web application.

ASF Overview

Ada Server Faces uses a model which is very close to Java Server Faces. JSF and ASF use a component-based model for the design and implementation of a web application. Like traditional MVC models, the presentation layer is separated from the control and model parts. Unlike the MVC model, JSF and ASF are not request-based meaning there is not a specific controller associated with the request. Instead, each component that is part of the page (view) participate in the control and each component brings a piece of the model.

This first article will focus on the presentation layer through a simple example.

Cylinder Volume Example

The example computes the volume of a cylinder. A simple form with two input fields allows to enter the cylinder dimensions (the unit does not matter).

Volume form

ASF Templating

The presentation part is implemented by a facelet file and a CSS file. The facelet file is an XML file which contains XHTML elements as well as facelets and JSF/ASF components. The facelets and ASF components are specified in their own XML namespace. The ASF components form a tree of components (UIComponent) which is then used for displaying and processing form submissions.

At the root of the XML file is an f:view component which represents the root of the component tree. The typical page layout looks as follows. Note the #{contextPath} notation in the link reference. This is an EL expression that will be evaluated when the view is displayed (rendered in JSF terminology).

<f:view contentType="text/html"
        xmlns:ui="http://java.sun.com/jsf/facelets"
        xmlns:f="http://java.sun.com/jsf/core"
        xmlns:c="http://java.sun.com/jstl/core"
	xmlns:u="http://code.google.com/p/ada-asf/util"
        xmlns:h="http://java.sun.com/jsf/html">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <link media="screen" type="text/css" rel="stylesheet"
      href="#{contextPath}/themes/main.css"/>
    <title>Volume Cylinder</title>
</head>
<body>
  <div>
     <h1>Compute the volume of a cylinder</h1>
     ...
  </div>
</body>
</html>
</f:view>

The form, input fields and submit buttons have to be specified using a JSF/ASF component. The JSF/ASF component will make the link between the presentation (view) and the controller (beans). The h:form is the JSF/ASF component that represents our form. Note that there is no need to specify any form action attribute: the form action will be managed by JSF/ASF.

The input fields are identified by the h:input components. The input field is linked to the bean through the value EL expression. This expression specifies the bean name and attribute. When rendering the view, JSF/ASF will fetch the value from the named bean. On form submission, JSF/ASF will populate the bean with the submitted value.

The h:input component can contain a f:converter element which indicates a conversion operation to call when displaying or before populating the bean value.

<h:form id='compute'>
  <dl>
    <dt>Height</dt>
    <dd>
      <h:inputText id='height' size='10' value='#{compute.height}'>
        <f:converter converterId="float" />
      </h:inputText>
    </dd>
    <dt>Radius</dt>
    <dd>
        <h:inputText id='radius' size='10' value='#{compute.radius}'>
           <f:converter converterId="float"/>
        </h:inputText>
    </dd>
    <dt></dt>
    <dd>
        <h:commandButton id='run' value='Compute'
       action="#{compute.run}"/>
    </dd>
  </dl>
</h:form>

At the form end, the h:commandButton represents the submit button and the controller action to invoke on form submission. The method to invoke is defined with an EL method expression in the action attribute. Before invoking the method, JSF/ASF will verify the submitted values, convert them according to associated converters, populate the beans with the values.

Style

The page style is provided by a specific CSS file. The dl/dt/dd list is rendered as a table using the following CSS definitions. By changing the CSS file, a new presentation can be provided to users.

dl {
  float: left;
  width: 500px;
  border: 1px solid #bcd;
  background-color: #ffffff;
  padding: 10px;
  -moz-border-radius: 6px;
  -webkit-border-radius: 6px 6px;
}
dt {
  clear: left;
  float: left;
  font-weight: bold;
  width: 20%;
  height: 20px;
  line-height: 24px;
  padding: 5px;
}
dd {
  float: left;
  padding: 5px;
}

Next time...

In this article, I've shown how to write the presentation and style part of an Ada Server Faces application. The next article will present the Ada beans that are associated with this example.

1 comments

Inserting a file in a JSF view with a custom component

By stephane.carrez 2009-01-26 20:56:20

Putting all this in a database is of course possible but it means that some administration interface is necessary when we change the blocks. Since the blocks are not intended to be changed too often, I prefered to have some simple solution and use plain text files for the storage.

The goal is now to make a JSF component that reads the file and insert it in the output page.

Step1: Write the UI Component class

The JSF component must inherit from UIComponentBase class. The class must implement the getFamily method to tell to what component family the component belongs.

 package example;
 public class UIFile extends UIComponentBase {
    public String getFamily() {
        return "UIFile";
    }
   ...
 }

The component only needs a file name as parameter. To make it simple, the file component is an attribute that cannot be bound to a value expression (ie, a #{xxx}). Define the file member and the accessor methods:

  public class UIFile extends UIComponentBase {
    protected String file;
    public String getFile() {
        return file;
    }
    public void setFile(String file) {
        this.file = file;
    }
  }

Now, the JSF component is ready and we need a renderer. To make it simple, you can make the component provide and implement the renderer. This is easier but you loose some flexibility. In our case, implementing the rendering in the JSF encodeBegin method is enough. To keep the example small, the file path must be absolute (in reality I'm using a servlet context parameter to configure the directory; this is left as an exercise :-)). To copy the file, I'm using the famous Apache IO library.

   import org.apache.commons.io.IOUtils;
   public class UIFile extends UIComponentBase {
    private static final char[] STOP = new char[0];
    public void encodeBegin(final FacesContext context)
      throws IOException {
        final String name = getFile();
        if (name == null || name.length() == 0) {
            return;
        }
        File f = new File(name);
        if (!f.exists()) {
            return;
        }
        final ResponseWriter rw = context.getResponseWriter();
        rw.writeText(STOP, 0, 0);
        FileInputStream is = null;
        try {
            is = new FileInputStream(f);
            final char[] data = IOUtils.toCharArray(is, "UTF-8");
            rw.write(data);
        } catch (IOException ex) {
        } finally {
            if (is != null) {
                try {
                    is.close();
                } catch (IOException ex) {
                }
            }
        }
   }
 }

For all this to work, there is a trick. The trick is that before writing the file content, we have to close any opened HTML element. This is done by calling writeText with an empty array. After that, the file data is written as is and unescaped.

Step2: Register the component in faces-config.xml

Once your UI component class is written, you have to register it in your faces-config.xml file:

    <component>
        <component-type>example.UIFile</component-type>
        <component-class>example.UIFile</component-class>
    </component>

Step3: Create the taglib

Then, write a taglib file. This is an XML file that tells Facelet the name of the tag in the XHTML file and how to bind that name to the new component.

 <facelet-taglib>
    <namespace>http://www.example.com/tool</namespace>
    <tag>
        <tag-name>insert</tag-name>
        <component>
            <component-type>example.UIFile</component-type>
        </component>
    </tag>
  </facelet-taglib>

Step4: Use the component

The last step is to use our new component in the XHTML file, this is as simple as this:

  <tool:insert file="myfile.html"/>
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