How To Load and Sort On Demand using Custom AbstractListModel and Sortable

{{Template:Smalltalk_Author|
|author=Edilson Alexandre Cuamba, Software Engineer, EXI - Engenharia e Comercialização de Sistemas Informáticos
|date=November 18, 2022
|version=ZK 9.6.1-Eval
}}

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= Overview =
Sometimes when you want to display data with a table structure, you use Listbox. This component is appropriate to it and works fine until your data gets huge and passes millions of rows; you will notice a little delay when you open the view with this component. For that reason, I needed to create a custom AbstractListModel that supports fetching only the data for the current page on the screen.
In this article, I will show you how to build your own CustomAbstractListModel<T> that supports pagination at the database layer.

Let’s see what we will build:

[https://i.imgur.com/EmHVXl5.gif .gif video showing the application]
<iframe src="https://i.imgur.com/EmHVXl5.gif"></iframe>

Let’s do it!



== Dependencies ==
To build this, we will need some functions. First is dependency injection (you can use other frameworks, but I personally like Spring) provided by Spring Framework. Second is the capacity to preserve the query structure, and change the structure during the pagination, for this, I use a library called search-jpa-hibernate. Relax, and I will show you how to configure this!

This is my build.gradle file:
https://github.com/EACUAMBA/loading_and_sorting_on__demand/blob/main/build.gradle
<syntaxhighlight lang='groovy'>
buildscript {
	repositories {
		mavenCentral()
	}
	dependencies {
		classpath("org.springframework.boot:spring-boot-gradle-plugin:2.5.12")
	}
}

apply plugin: 'java'
apply plugin: 'war'
apply plugin: 'org.springframework.boot'
apply plugin: "idea"

idea{
	module {
		setDownloadSources(true)
		setDownloadJavadoc(true)
	}
}

repositories {
	mavenLocal()
	maven { url "https://mavensync.zkoss.org/maven2" }
	maven { url "https://mavensync.zkoss.org/eval" }
	mavenCentral()
}

sourceCompatibility = '1.8'
targetCompatibility = '1.8'

ext {
	zkspringbootVersion = '2.5.12'
	springbootVersion = '2.5.12'
	zkspring = '4.0.0'
	zkVersion = '9.6.0'
	zatsVersion = '3.0.0'
	junitVersion = '4.13.1'
	searchJPAHibernateVersion = '1.2.0'
	lombokVersion = '1.18.24'
	mysqlVersion = '8.0.31'
	javaxServerletAPIVersion='4.0.1'
	commonsLang3Version='3.12.0'
}

configurations.testImplementation {
	// conflicts with ZATS (which is using jetty)
	exclude module: "spring-boot-starter-tomcat"
}

dependencies {
	implementation ("org.zkoss.zkspringboot:zkspringboot-starter:${zkspringbootVersion}")
	providedRuntime("javax.servlet:javax.servlet-api:${javaxServerletAPIVersion}")

	implementation ("org.zkoss.zk:zkspring-core:${zkspring}")
	implementation("org.zkoss.zk:zkplus:${zkVersion}")
	implementation ("org.springframework.boot:spring-boot-starter-data-jpa:${springbootVersion}")
	compileOnly ("org.springframework.boot:spring-boot-devtools:${springbootVersion}")
	implementation ("com.googlecode.genericdao:search-jpa-hibernate:${searchJPAHibernateVersion}")
	implementation("mysql:mysql-connector-java:${mysqlVersion}")

	compileOnly("org.projectlombok:lombok:${lombokVersion}")
	annotationProcessor("org.projectlombok:lombok:${lombokVersion}")
	testImplementation "org.springframework.boot:spring-boot-starter-test:${springbootVersion}"
	implementation("org.apache.commons:commons-lang3:${commonsLang3Version}")

	testImplementation "org.zkoss.zats:zats-mimic-ext96:${zatsVersion}"
	testImplementation "junit:junit:${junitVersion}"
}
</syntaxhighlight>

These are some of the dependencies I like to use, so feel free to remove the ones you don't need.
Now let’s build our Custom AbstractListModel<T>.

== code snippet ==
<syntaxhighlight lang='java'>
public class ImageSaver {

public void save(String imageDataUrl) throws IOException {
        //Sample Code for code syntax
    }
}
</syntaxhighlight>

== Inline Code == 
This is an <code>Inline Code</code>

= Download = 
If you want to check the running code please this is the repository at github.com.
https://github.com/EACUAMBA/loading_and_sorting_on__demand

= Summary =
A short conclusion, welcome feedback

=Comments=
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