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composite-view/README.md
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@ -10,26 +10,28 @@ tags:
- Presentation - Presentation
--- ---
## Name
**Composite View**
## Intent ## Intent
The purpose of the Composite View Pattern is to increase re-usability and flexibility when creating views for websites/webapps. The purpose of the Composite View Pattern is to increase re-usability and flexibility when creating views for websites/webapps.
This pattern seeks to decouple the content of the page from its layout, allowing changes to be made to either the content This pattern seeks to decouple the content of the page from its layout, allowing changes to be made to either the content
or layout of the page without impacting the other. This pattern also allows content to be easily reused across different views easily. or layout of the page without impacting the other. This pattern also allows content to be easily reused across different views easily.
## Explanation ## Explanation
Real World Example
Real-world example
> A news site wants to display the current date and news to different users > A news site wants to display the current date and news to different users
> based on that user's preferences. The news site will substitute in different news feed > based on that user's preferences. The news site will substitute in different news feed
> components depending on the user's interest, defaulting to local news. > components depending on the user's interest, defaulting to local news.
In Plain Words In plain words
> Composite View Pattern is having a main view being composed of smaller subviews. > Composite View Pattern is having a main view being composed of smaller subviews.
> The layout of this composite view is based on a template. A View-manager then decides which > The layout of this composite view is based on a template. A View-manager then decides which
> subviews to include in this template. > subviews to include in this template.
Wikipedia Says Wikipedia says
> Composite views that are composed of multiple atomic subviews. Each component of > Composite views that are composed of multiple atomic subviews. Each component of
> the template may be included dynamically into the whole and the layout of the page may be managed independently of the content. > the template may be included dynamically into the whole and the layout of the page may be managed independently of the content.
> This solution provides for the creation of a composite view based on the inclusion and substitution of > This solution provides for the creation of a composite view based on the inclusion and substitution of
@ -42,6 +44,7 @@ Since this is a web development pattern, a server is required to demonstrate it.
This example uses Tomcat 10.0.13 to run the servlet, and this programmatic example will only work with Tomcat 10+. This example uses Tomcat 10.0.13 to run the servlet, and this programmatic example will only work with Tomcat 10+.
Firstly there is `AppServlet` which is an `HttpServlet` that runs on Tomcat 10+. Firstly there is `AppServlet` which is an `HttpServlet` that runs on Tomcat 10+.
```java ```java
public class AppServlet extends HttpServlet { public class AppServlet extends HttpServlet {
private String msgPartOne = "<h1>This Server Doesn't Support"; private String msgPartOne = "<h1>This Server Doesn't Support";
@ -91,12 +94,13 @@ public class AppServlet extends HttpServlet {
} }
} }
``` ```
This servlet is not part of the pattern, and simply forwards GET requests to the correct JSP. This servlet is not part of the pattern, and simply forwards GET requests to the correct JSP.
PUT, POST, and DELETE requests are not supported and will simply show an error message. PUT, POST, and DELETE requests are not supported and will simply show an error message.
The view management in this example is done via a javabean class: `ClientPropertiesBean`, which stores user preferences. The view management in this example is done via a javabean class: `ClientPropertiesBean`, which stores user preferences.
```java ```java
public class ClientPropertiesBean implements Serializable { public class ClientPropertiesBean implements Serializable {
@ -136,11 +140,13 @@ public class ClientPropertiesBean implements Serializable {
// getters and setters generated by Lombok // getters and setters generated by Lombok
} }
``` ```
This javabean has a default constructor, and another that takes an `HttpServletRequest`. This javabean has a default constructor, and another that takes an `HttpServletRequest`.
This second constructor takes the request object, parses out the request parameters which contain the This second constructor takes the request object, parses out the request parameters which contain the
user preferences for different types of news. user preferences for different types of news.
The template for the news page is in `newsDisplay.jsp` The template for the news page is in `newsDisplay.jsp`
```html ```html
<html> <html>
<head> <head>
@ -198,6 +204,7 @@ The template for the news page is in `newsDisplay.jsp`
</body> </body>
</html> </html>
``` ```
This JSP page is the template. It declares a table with three rows, with one component in the first row, This JSP page is the template. It declares a table with three rows, with one component in the first row,
two components in the second row, and one component in the third row. two components in the second row, and one component in the third row.
@ -205,7 +212,9 @@ The scriplets in the file are part of the
view management strategy that include different atomic subviews based on the user preferences in the Javabean. view management strategy that include different atomic subviews based on the user preferences in the Javabean.
Here are two examples of the mock atomic subviews used in the composite: Here are two examples of the mock atomic subviews used in the composite:
`businessNews.jsp` `businessNews.jsp`
```html ```html
<html> <html>
<head> <head>
@ -233,7 +242,9 @@ Here are two examples of the mock atomic subviews used in the composite:
</body> </body>
</html> </html>
``` ```
`localNews.jsp` `localNews.jsp`
```html ```html
<html> <html>
<body> <body>
@ -259,11 +270,15 @@ Here are two examples of the mock atomic subviews used in the composite:
</body> </body>
</html> </html>
``` ```
The results are as such: The results are as such:
1) The user has put their name as `Tammy` in the request parameters and no preferences: 1) The user has put their name as `Tammy` in the request parameters and no preferences:
![alt text](etc/images/noparam.PNG) ![alt text](etc/images/noparam.PNG)
2) The user has put their name as `Johnny` in the request parameters and has a preference for world, business, and science news: 2) The user has put their name as `Johnny` in the request parameters and has a preference for world, business, and science news:
![alt text](etc/images/threeparams.PNG) ![alt text](etc/images/threeparams.PNG)
The different subviews such as `worldNews.jsp`, `businessNews.jsp`, etc. are included conditionally The different subviews such as `worldNews.jsp`, `businessNews.jsp`, etc. are included conditionally
@ -304,6 +319,7 @@ that are included in the page dynamically. Most modern Javascript libraries, lik
with components. with components.
## Consequences ## Consequences
**Pros** **Pros**
* Easy to re-use components * Easy to re-use components
* Change layout/content without affecting the other * Change layout/content without affecting the other
@ -316,10 +332,11 @@ with components.
* Increases potential for display errors * Increases potential for display errors
## Related patterns ## Related patterns
* [Composite (GoF)](https://java-design-patterns.com/patterns/composite/) * [Composite (GoF)](https://java-design-patterns.com/patterns/composite/)
* [View Helper](https://www.oracle.com/java/technologies/viewhelper.html) * [View Helper](https://www.oracle.com/java/technologies/viewhelper.html)
## Credits ## Credits
* [Core J2EE Patterns - Composite View](https://www.oracle.com/java/technologies/composite-view.html) * [Core J2EE Patterns - Composite View](https://www.oracle.com/java/technologies/composite-view.html)
* [Composite View Design Pattern – Core J2EE Patterns](https://www.dineshonjava.com/composite-view-design-pattern/) * [Composite View Design Pattern – Core J2EE Patterns](https://www.dineshonjava.com/composite-view-design-pattern/)