My Sql + Spring Boot JPA - One to many, many to one example

This is a simple spring boot JPA (hibernate) example. It will demonstrate how one to many, many to one mapping can be done

Below are the tables created in MySQL

create table department

(

 department_id int not null auto_increment,primary key (department_id),

 department_name  varchar(50) not null

);

create table employee

(

 employee_id int not null auto_increment, primary key (employee_id),

 employee_name varchar(50) not null, 

 department_id int not null, foreign key (department_id) references department(department_id)

);

pom.xml

application.yml

Java - Export database table to CSV file

This is a sample springboot application with bare minimum code to export database tables to CSV file

pom.xml

application.yml

Application.java

Java - Export database tables to an excel file

This is a sample springboot application with bare minimum code to export database tables to an excel file

pom.xml

application.yml

Application.java

Spring Boot + ReactJS hello world example

Spring Boot is designed to get you up and running as quickly as possible, with minimal upfront configuration of Spring. To know more about spring boot, click here.

ReactJS is a JavaScript library used for building user interfaces. To know more about react, click here.

In this example spring boot will exposed our business logic using rest endpoints and reactjs is used as frontend user interface. Point here to be noted is unlike a traditional web application where java codes + web code (HTML + javascript + css) are residing in same project here spring boot and reactjs will be in different project. The main advantage of this type of setup is to have a loose coupling between your UI and business logic. Tomorrow if you feel to replace reactjs with anjularjs or vuejs you can very well do it without touching business logic.

Step 1 -
Create a spring boot application, click here for more details.

pom.xml

Simple spring integration with springboot

In this example we will see a simple file poller application using spring integration. It will poll for a file in a particular location at certain interval and if file is found it will move it to another location.

There are 3 core components of spring integration -

Messages - Messages are the objects sent from one component to another. In our case a file is sent from file poller to file handler.
Channels - Assume channels are the network (a pipe) by which messages are sent from one component to another.
Adapters - Adapters route the output from one channel to the input of another one.

Please see the codes below -

Integration of DWR using DWRSpringServlet

DWR is a Easy Ajax for Java. To know more click here.

In this article we will see sample codes for integration of DWR with DWRSpringServlet

Step 1 - Create a web project in eclipse.

Step 2 - Add below Spring libraries

• Spring Core libraries
• Spring Web libraries
• Spring AOP libraries

Step 3 - Add dwr.jar

Download appropriate version of dwr.jar and add it in your application classpath. For example DWR 3 requires Spring version 2.5 or greater.

Step 4 - Create dependent files

web.xml

The DwrSpringServlet can be used if you are not using Spring MVC. This servlet gains access to the Spring context configured in your web.xml. You can create your own context file, in our case it is dwrcontext.xml.

dwrcontext.xml

DWRService.java

index.jsp

Step 5 - Deploy the project in tomcat (or any other web server) and check the output

Integration of DWR using Spring MVC

DWR is a Easy Ajax for Java. To know more click here.

In this article we will see sample codes for integration of DWR with spring MVC

Step 1 - Create a web project in eclipse.

Step 2 - Add below Spring libraries

• Spring Core libraries
• Spring Web libraries
• Spring AOP libraries

Step 3 - Add dwr.jar
Download appropriate version of dwr.jar and add it in your application classpath. For example DWR 3 requires Spring version 2.5 or greater.

Step 4 - Create dependent files

web.xml
Create spring DispatcherServlet and map URL pattern as shown below

javaxp-servlet.xml
If you are using Spring MVC you must declare dwr controller and url mapping i.e. SimpleUrlHandlerMapping as shown below

DWRService.java

index.jsp

Step 5 - Deploy the project in tomcat (or any other web server) and check the output

Spring bean syntax

1. Import resources

Below is the syntax to import resources from various files. It is helpful when you want to bifurcated beans and database configuration in separate files and merger everything into single servlet. Here you can provide absolute or relative path of the source file.

<beans>
<import resource="file1.xml" />
<import resource="../file2.xml" />
</beans>

2. Spring MVC Dispatcher Servlet, syntax to load XMLs using init param

You can use it in web.xml file to XMLs using init param. You can load various XMLs like  beans and database configuration etc.

<web-app>
    <servlet>
        <servlet-name>test</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>            
            <param-name>contextConfigLocation</param-name>
            <param-value>
                /WEB-INF/test/*.xml
            </param-value>        
        </init-param>        
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>test</servlet-name>
        <url-pattern>/test/*.do</url-pattern>
    </servlet-mapping>
</web-app>

3. Url Handler Mapping syntax

Below is the example for Mapping URLs with respective beans, this is useful when you want to keep all URLs mapping together at one place.

<beans>

    <bean id="handlerMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
        <property name="mappings">
        <props>
            <prop key="/sfc.do">simpleFormController</prop>
            <prop key="/mac.do">multiActionController</prop>
        </props>
        </property>
    </bean>


    <bean id="simpleFormController" class="com.javaxp.FormController" autowire="byName">
        <property name="commandName" value="formBean"></property>
        <property name="commandClass" value="com.javaxp.FormBean"></property>
        <property name="formView" value="form"></property>
        <property name="successView" value="submit"></property>        
    </bean>

    <bean id="multiActionController" class="org.springframework.web.servlet.mvc.multiaction.ParameterMethodNameResolver">
<property name="paramName" value="action" />
<property name="defaultMethodName" value="defaultPage" />
    </bean>

</beans>

Spring - How to inject List or Map using bean?

In this example we will see how to How to inject List or Map using Spring bean. For complete setup using eclipse you can refer my previous article, Spring Hello World Example.

About the example - We have a class Country.java with two instance variables city as Map and president as List. We will set those values using Spring bean with the help of Spring configuration file  applicationContext.xml. Please see the self explanatory codes below

Country.java.

Spring : MultiActionController Example

Lets create a webproject in My Eclipse (lets say MultiActionController). Now we will add spring Capabilities to it. Here we are using Spring 3.0


(Right click on project) -> My Eclipse -> Add Spring Capabilities..


Adding below libraries (as shown in below image)

• Spring 3.0 Core Libraries
• Spring 3.0 Web Libraries

Spring : SimpleFormController Example

Before understanding SimpleFormController you must understand its Spring bean lifecycle. Below diagram tries to explain you the flow of SimpleFormController. 

• Whenever a request comes from browser it checks in deployment descriptor (i.e Web.xml) for its servlet and url mapping. 
• Then request goes to its corresponding dispatcher-servlet.xml, The DispatcherServlet consults the HandlerMapping and invokes the Controller associated with the request in our case its SimpleFormController.
• The Controller process the request by calling the appropriate service methods i.e isFormSubmitted(). Here you can write your own logic of a form being submitted or not. Usually if a request object is empty its a first time request and it returns false. 
• formBackingObject() method will be called regardless of form is submitted or not however formBackingObject() method will return FormBean Object to formView when form is not submitted and ModelAndView Object to successView when form is submitted. 
• Then request goes to a ViewResolver to find the actual View to invoke. The View with the help of the FormBean or ModelAndView will render the result back to the user.

Lets create a webproject in My Eclipse (lets say SpringFormController). Now we will add spring Capabilities to it. Here we are using Spring 2.5


(Right click on project) -> My Eclipse -> Add Spring Capabilities..

JSTL : How to use fmt:message and ResourceBundle

There are two ways you can access values from a property file. Mostly a text value which can change in future are kept in property file and access it using fmt:message and ResourceBundle in JSP and JAVA respectively so that if the text values are changed in future it wont affect our code. We just need to change in property file and rest all will be taken care implicitly.

Lets see how to use fmt:message and ResourceBundle in JSP and JAVA respectively.

1. In JSP

If you need to access the property value in JSP, first lets create a property file lets say prop.properties. Add prop.properties in src folder of your application.

prop.properties

key1=This is value1
key2=This is value2

Add the mapping in web.xml or Spring's dispatcher-servlet.xml as shown below

<bean id="messageSource" class="org.springframework.context.support.ResourceBundleMessageSource">
<property name="basename" value="prop" />
</bean>

Note the value="prop" it says to load prop.properties from the src folder. Now through JSP you can access the property by its key as shown below

<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt" %>

<fmt:bundle basename="prop">
<fmt:message key="key1"/>
<fmt:message key="key2"/>
</fmt:bundle>

2. In Java

Also you may need to access these properties in a JAVA program it could be either bean or any controller. You can access using java.util.ResourceBundle as shown below.

String value1 = ResourceBundle.getBundle("prop").getString("key1");
String value2 = ResourceBundle.getBundle("prop").getString("key2");

Note : You may get below error

org.apache.jasper.JasperException: The absolute uri: http://java.sun.com/jsp/jstl/fmt cannot be resolved in either web.xml or the jar files deployed with this application

To solve above error you need to include jstl-1.2.jar in your application's classpath. It could be possible that your application is not able to detect jstl-1.2.jar file.

Spring Hello World Example

For running this example we have used MyEclipse 8.6.1, to download Latest version of MyEclipse go to below URL

http://www.myeclipseide.com/

Step by step tutorial to implement Spring hello world example

Step 1. Create a New Java Project

New -> Java Project