JAVA application design principles

Purpose of this guide

This guide is intended to give the principles for the application design. They should be implemented as a good practice.

Layering

When layering an application, you should consider:

-          Action layer for processing data significant regarding to the business

-          Model interface for carrying data significant to the business

-          Transverse component for processing data that are not significant for the business

An application shall have three important action layer

-          Data

-          Services

-          Exposure : HMI – WS - Reporting

Each of the interface between those layers is done by a set of classes named model interfaces.

-          Data model: is the separation between DAO and Service

-          Data Transfer Object model implements the model for exchanging with exposure layer. You can have HMIDTO, WSDTO and Reporting DTO. Actually, you can have as many

Apart from those two major class, you may have the transverse layer

-          Utility classes, for sharing common routines in classes

-          Formatting, internationalization and conversion classes

-          System interface classes

Action layer

For the interface between action layers you shall use models

Data Layer

The data layer is typically in charge of communicating with the lower layer. DAO communicates with services using the object model.

Service Layer

The service layer contains the actions that make sense for the business. They are named upon there objective. For instance, the service named EmployeeService will group the methods applying to an employee.  

In large project, it is a good practice to have one service for each Exposure Layer. For instance, you would have:

-          EmployeeHMIService for performing task linked to HMI

-          EmployeeWSService for performing task linked to the Web Service Apis

However, this rule maybe unworthy on small projects.

Services communicates with the exposure service using DTO (data transfer objects)

This service separation is done thanks to packages

Model interfaces

Data Access Model

Data access model is something very close from the structure in the database.

It is a good principle not to reuse the data model interface for the exchange with the exposure layer in order to guarantee a good layer separation.

Data Transfer Model

The data transfer model is used to connect with the exposure layer. It only contains the data necessary to the upper level.

It has not to be uniquely bound to a same concept. For instance, if you have a table displaying a list of employees with only name and first name. You may have a bean with only two fields. While, if you want to produce a screen with the employee detail, you may create a DTO with all the employee fields.

It is a good practice to closely to transform the Data Access Model with some specific methods of the service.

For instance, you would have two methods in the employee service

-          EmployeeDetailHMIDTO  transformEmployee2EmployeeDetailHMI(Employee)

-          EmployeeListHMIDTO  transformEmployee2EmployeeListHMI(Employee)

Tranverse component

SQL server pour les Gros Nuls

Créer une database

create database "db-test";
CREATE LOGIN "user-test" WITH PASSWORD = 'mypassword';
GO
USE "db-test";
CREATE USER "user-test" FOR LOGIN "user-test" WITH DEFAULT_SCHEMA = dbo;
EXEC sp_addrolemember N'db_datawriter', N'user-test'
EXEC sp_addrolemember N'db_datareader', N'user-test'
-- If you want a case sensistive database
ALTER DATABASE "db-test" COLLATE Latin1_General_CS_AS; 

Change ownership of a database

ALTER AUTHORIZATION DATABASE: to

Déplacer les fichiers d'une base de données pour libérer de l'espace

 

• Récupperer les infos sur l'endroit ou se trouvent les fichier de log et de données en allant sur l'onglet propriété--> File de la base de donnée

• Détacher la db

sp_detach_db my_db 

• Copier les fichiers

• Rattacher la db

EXEC sp_attach_db @dbname = N'corete_mja',  
    @Core TE =  
N'F:\data\Core TE_mja1.mdf',  
    @Core TE_log =  
N'F:\data\Core TE_log_mja1.ldf'; 
 
Ligne de commande
Faire un backup
Ligne de commande

BACKUP DATABASE "dbname" TO DISK='D:\data\act\dumps\finename.BAK'

Interactive client
Se placer sur la db et lancer un backup ar le client SQL Server Management Studio 

Restorer une database 

Ligne de commande

USE [master];
GO
CREATE DATABASE dbint;
RESTORE DATABASE dbint  FROM DISK = 'd:\youbackup-int.bak' with replace;

ALTER AUTHORIZATION ON DATABASE::dbint TO existingloginfordbint

Parfois vous pouveez être bloqué dans la restauration parce que les chemins du serveurs de destination ne correspondent pas au serveur source. Dans ce cas il faut utiliser l'opérateur move.

RESTORE DATABASE actint  FROM DISK = 'f:\share\dbint.bak' WITH REPLACE,
 MOVE 'dbint' TO 'C:\Program Files (x86)\Microsoft SQL Server\MSSQL11.MSSQLSERVER1\MSSQL\DATA\dbint.mdf',
MOVE 'dbint_log' TO 'C:\Program Files (x86)\Microsoft SQL Server\MSSQL11.MSSQLSERVER1\MSSQL\DATA\dbint.ldf' ;

Pour lister le nom des data et journaux utiliser la commande FILELISTONLY

RESTORE FILELISTONLY FROM DISK = 'f:\share\act-readonly.bak';

Create a SQL script

Pour créer un script SQL et récupper le contenu d'un table:

Etudier les performances

SELECT  creation_time
        ,last_execution_time
        ,total_physical_reads
        ,total_logical_reads
        ,total_logical_writes
        , execution_count
        , total_worker_time
        , total_elapsed_time
        , total_elapsed_time / execution_count avg_elapsed_time
        ,SUBSTRING(st.text, (qs.statement_start_offset/2) + 1,
         ((CASE statement_end_offset
          WHEN -1 THEN DATALENGTH(st.text)
          ELSE qs.statement_end_offset END
            - qs.statement_start_offset)/2) + 1) AS statement_text
FROM sys.dm_exec_query_stats AS qs
CROSS APPLY sys.dm_exec_sql_text(qs.sql_handle) st
ORDER BY total_elapsed_time / execution_count DESC; 

Gérer les fichiers

Reduire un fichier de log

DBCC SHRINKFILE (DBWV1Y6101_log,20)

Déplacer la base de donnée temporaire

ALTER DATABASE tempdb   
MODIFY FILE (NAME = tempdev, FILENAME = 'E:\SQLData\tempdb.mdf');  

ALTER DATABASE tempdb   
MODIFY FILE (NAME = templog, FILENAME = 'F:\SQLLog\templog.ldf');  
 

Restore in amazon

exec msdb.dbo.rds_restore_database
@restore_db_name='mydb',
@s3_arn_to_restore_from='arn:aws:s3:::mys3bucket/mydimp.bak';

Load from a script

sqlcmd -S localhost -i "D:\data\Core kpi\dump\script.sql" -o "D:\data\Core kpi\dump\script.txt" 

sqlcmd -S server,port -r1 -Uusername -Ppassword -b -ddatabase -iinputfile

Remove dead code from your application

The problem:
Code coverage estimation is mostly based on Automated Unit Testing and software like JUnit. Doing like this is okay to increase youy coverage rate, but sometimes has a pernicious effect. Because it does not guarantee that the code you cover is really necessary to your application, and so you may have some portions of code covered but unrelevant for the actual application business.

Unecessary code detected with UCDetector:
In order to avoid this unecessary code, you have several alternatives. The first is to use the excellent eclipse plugin UCDetector (standing for Unecessary Code Detector) downloadable at http://www.ucdetector.org/. This detects in a friendly way the code that is not referenced elsewhere in the project.

This plugin must be applied to relevant package for application business. Indeed,  service packages and dao packages are good candidates. The result comes in the markers tabs of eclipse. You can then decide weither or not, those method shall be kept or not. 

Unecessary code detected with Tomcat and code coverage:
The below method can only apply to the low layer in a webapp, because you cannot check the code accessed throught JSP. For an in deep investigation of the actual code used, you may use cobertura and tomcat together.

Supposing you have a maven project. Here is the way to do it.
First, build your package :
- mvn package

The project is built in the target/myproject.war archive.

- mvn cobertura:instrument

This creates a folder named
- target\generated-classes\cobertura containing the instrumented classes.

This also creates a file named :

- target\cobertura.ser this files is a database storing the coverage information.

We have to build an instrumented war.

- Unzip the myproject.war file in the folder myproject
- Copy the cobertura.jar file in the myproject/WEB-INF/lib folder
- Replace the classes in folder myproject/WEB-INF/classes by the one produced in target\generated-classes\cobertura

Now it is time to prepare your tomcat:
Copy the cobertura.ser file in the folder where you will launch tomcat. If you are lauching tomcat through the windows explorer,  this folder is the /bin/ directory. If your are lucnhing it through a console, the folder is the current working directory.

Now you can run your tomcat.

Finally produce your report using the command

cobertura-report.bat --datafile ./cobertura.ser --destination ../report --format html ../sources/

Specials if you have your project distibuted in several modules^, you may first merge your cobertura information into a single file before launching tomcat :

cobertura-merge.bat --datafile target/cobertura_final.ser ../myproject-service/target/cobertura/cobertura.ser ../myproject-webapp/target/cobertura/cobertura.ser

Dynamic image upload like in facebook

Doing like facebook for uploading an image will make your web site instinctive. The main difficulty for making it is that you cannot post any multimedia object using AJAX, you must submit the image from a form within the web page. That is why you have to declare a "virtual" form (not accessible directly for input): To do it in java, here is the tip: In your JSP page add the virtual form:

<div class="row-fluid">
    <div class="span2 vertical-align">
    <img id="pictureImg" class="hidden"    src="showPicture.action" />
</div>

In your JSP page add the virtual form:

<!-- Div to upload image (replace original) -->
<div id="uploadDiv">
    <s:form target="upload_target"
        action="UploadPicture"
        enctype="multipart/form-data" id="pictureForm">
        <ul class="error">
            <li id="fileUploadErrorExtension" class="hidden"><s:text
                    name="picture.error.extension" /></li>
            <li id="fileUploadErrorSize" class="hidden"><s:text
                    name="picture.error.size" /></li>
        </ul>
        <div class="picture" id="picture">
            <input type="file" id="pictureFile"
                name="pictureFile" />
            <div class="message hidden" id="pictureMessage">
                <s:text name="picture.change" />
            </div>
        </div>
    </s:form>
    <iframe id="upload_target" name="upload_target" src="#"
        style="width: 0; height: 0; border: 0px solid #fff;"></iframe>
</div>

In your page JS, you must add

<script language="javascript" type="text/javascript">
    window.top.window.etlb.Utils.upload.callback();
</script>

This binds HTML with JAVA script

"use strict";
// At window loading the variables of JS are initialized. 
$(window).load(function() {
        Global.Utils.upload.url = 'displayPicture.action';
        // Binds the pictureImg to the variable in JS file.
        Global.Utils.upload.img = $('#pictureImg');
        Global.Utils.upload.initUpload();
});



var Global = {
    Utils : {
        upload : {
            // global var to store the image, url to get the new img
            url : null,
            img : null,
            callback : function() {
                // callback of server : reinit upload the random prevent from caching the image.
                Global.Utils.upload.img.attr('src', Global.Utils.upload.url
                        + '?random=' + Math.random());
                Global.Utils.upload.img.bind("load",function(){
                Global.Utils.upload.initUpload();
                });
            },

            initUpload : function() {
                // Replace initial image with a div background by the upload div and hides the image
                Global.Utils.upload.img.addClass('hidden');
                Global.Utils.upload.img.after($('#uploadDiv'));                                                            
                $('#picture').css(
                        'background-image',
                        'url(\'' + etlb.Utils.upload.img.attr('src')+ '\')');
                // When the mouse enters the image, the change image label is displayed
                $('#picture').mouseenter(function() {
                    $('#pictureMessage').removeClass('hidden');
                });
                // When the mouse enters the image, the change image label is hidden
                $('#picture').mouseleave(function() {
                    $('#pictureMessage').addClass('hidden');
                });

                var extension = [ 'jpg', 'jpeg', 'png', 'bmp', 'gif' ];
                $('#fileUploadErrorExtension').text(
                        'Error Uploading');
                var validFileExtension = function(fileName) {
                    for ( var i in extension) {
                        if (fileName.toLowerCase().indexOf(
                                '.' + extension[i].toLowerCase()) != -1) {
                            return true;
                        }
                    }
                    return false;
                };
                var validFileSize = function(size) {
                    return size <= 1024 * 1000;
                };
                // When the picture file is changed you upload the image by sumbitting the form.
                
                $('#pictureFile').change(function(e) {
                    var input = this;
                    var fileName = '';
                    var fileSize = '';
                    if ($.browser.msie && e.target.value) {
                        fileName = e.target.value;
                        fileSize = '1000';
                    } else if (input.files && input.files[0]) {
                        fileName = input.files[0].name;
                        fileSize = input.files[0].size;
                    }
                    if (!validFileExtension(fileName) && fileName != '') {
                        $('#fileUploadErrorExtension').removeClass('hidden');
                        return;
                    }
                    if (fileName == '') {
                        $('#fileUploadErrorExtension').addClass('hidden');
                    }

                    if (!validFileSize(fileSize)) {
                        $('#fileUploadErrorSize').removeClass('hidden');
                        return;
                    }

                    $('#fileUploadErrorExtension').addClass('hidden');
                    $('#fileUploadErrorSize').addClass('hidden');
                    
                    // Send
                    $('#pictureForm').submit();

                });

            }
        }
    }
};