Posted: June 14, 2012 in Techilla

Great post on Performance monitoring using Hibernate

Thoughts on...

Performance monitoring is, by its very nature, a slippery slope. Once you start looking for inefficiencies in code, it’s easy to get carried away wanting to optimize every last line for supreme efficiency. It’s thus important to balance the value of an optimization versus the time spent investigating the proper fix, the effort and difficulty required to implement it, and its importance relative to other things on the roadmap.

Every environment, every team, and every piece of software is different – so I won’t dare try to formulate any hard and fast rules for what is an appropriate or inappropriate amount of optimization. Suffice it to say, before any decisions can be made as to whether an optimization should be implemented, the nature of the problem must be understood. Below I will show how to use functionality built into Hibernate to help understand where the performance issues in your application…

View original post 1,669 more words

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Today, we are going to put forth a small EJB 3 application in Glassfish v3.

Why EJB3?

 Coding in EJB3 is almost as simple as it gets. EJB has gone some major intuitive simplifications in order of coding from releases 2x to 3x.

Gone are the days of cumbersome home interfaces, remote interfaces, deployment descriptors and checked exceptions in SessionBean implementations.

EJB3 supports annotation based coding and dependency injections. While we can (and will ) do the JNDI lookups to get hold of an EJB/Resource, DI takes away the need to do so.

 While the deployment descriptors (xml based) can still be used, we are going to develop a simple application which will be wholly annotation based.

Why Glassfish?

Glassfish is probably the easiest application server out there. It’s so intuitive that it almost feels like a web server. We will eventually use the same application in a Weblogic server(the big daddy) but Glassfish is great because you can start it up and test concepts in almost no time.

Lets then put the 2 heads together and  build a small EJB3 application and deploy it in Glassfish v3.

We will be doing this in Windows and we shall use Eclipse as our IDE.

Pre-requisites

Download the zip file –  glassfish 3x.zip

Our version : glassfish-3.1.2.

Startup of Glassfish

Go to the bin directory after unzipping and key in the following(or start up asadmin.bat)

asadmin start-database ( If you really need Derby to start)
asadmin start-domain

Open http://localhost:4848/asadmin. to test the installation.

 Login using the user ID admin and password adminadmin. This will validate the installation.

Coding our EJBs

We only need a POJI and a POJI and then we will add some simple annotations to magically turn the POJO to an EJB. We will be using here a stateless session bean.

@Remote
public interface PlaceAuctionItem {
	void placeAuctionItem();
}


@Stateless(name="PlaceAuctionItem", mappedName="ejb/PlaceAuctionItem")
public class PlaceAuctionItemBean implements PlaceAuctionItem{


	@Override
	public void placeAuctionItem() {
		System.out.println("saving the AuctionItem ");
		//save the auctionItem in the database
		
	}
	 

}

Annotations:

@Stateless: marks the session bean as stateless

mappedName: would be used to do JNDI lookup from the client

@Remote: tells that this is the remote interface.

Once done, we need to deploy the EJB to Glassfish

 EJB Deployment in Glassfish

  • Right click and Export the project as a jar file(let’s name it as test-ejb.jar) and deploy it to

                glassfish-3.1.2\glassfish3\glassfish\domains\domain1\autodeploy\test-ejb.jar

  • Glassfish auto redeploys the jar file, so every time you change anything on the EJBs, you have to re-export the jar(obviously) but you don’t have to restart the server.

Check out the image below.(ActionBazaar is our project name in Eclipse)

export ejb jar eclipse glassfish

Once we have done this, we would create the client which will be a simple java class to test our EJBs.

EJB Client

public class TestStatelessSessionBeans {
@EJB
private PlaceAuctionItem placeAuctionItem;

public void mimicPlaceAuctionItem(){
	placeAuctionItem.placeAuctionItem();
}

public TestStatelessSessionBeans() {
	super();

	try {
		Properties props = new Properties();
		props.put(Context.INITIAL_CONTEXT_FACTORY, 							"com.sun.enterprise.naming.SerialInitContextFactory");
		props.setProperty("org.omg.CORBA.ORBInitialHost", "localhost");

		// glassfish default port value will be 3700,
															props.setProperty("org.omg.CORBA.ORBInitialPort", "3700");

		InitialContext ctx = new InitialContext(props);
			
		this.placeAuctionItem = (PlaceAuctionItem) 								ctx.lookup("ejb/PlaceAuctionItem");
	} catch (NamingException e) {
		e.printStackTrace();
	}

}

public class TestModule {
	public static void main(String args[]){
	   new TestStatelessSessionBeans().mimicPlaceAuctionItem();
	}
}

Some common errors

• @EJB will also mark this EJB to be DI by the container, however, we are not deploying the client in Glassfish, and hence we would need to do the JNDI lookup.

• We have to use the properties mentioned while instantiating the InitialContext to prevent error:

Lookup failed for ‘ejb/PlaceAuctionItem’ in SerialContext[myEnv={java.naming.factory.initial=com.sun.enterprise.naming.impl.SerialInitContextFactory, java.naming.factory.url.pkgs=com.sun.enterprise.naming, java.naming.factory.state=com.sun.corba.ee.impl.presentation.rmi.JNDIStateFactoryImpl} [Root exception is javax.naming.NameNotFoundException: PlaceAuctionItem not found]

Or

javax.naming.NoInitialContextException: Need to specify class name in environment or system property, or as an applet parameter, or in an application resource file: java.naming.factory.initial

Libs required by project

  • appserv-rt.jar
  • gf-client.jar
  • javaee.jar

 But take note, that the gf-client.jar must not be copied into your workspace. It needs to be referenced from the Glassfish server location. It acts like a wrapper for other glassfish client libraries.

Now, if we run the client, and see the server.log under domains/domain1/logs we get the following statement printed from our StatelessSessionBean.

[#|2012-06-06T01:20:12.346+0800|INFO|glassfish3.1.2|javax.enterprise.system.std.com.sun.enterprise.server.logging|_ThreadID=20;_ThreadName=Thread-2;|saving the AuctionItem AuctionItem

Next up would be deploying an ear into Glassfish(which shall contain this EJB and a servlet to test our DI)

Calcutta

Posted: May 23, 2012 in Uncategorized

Calcutta.

Inheritance vs Aggregation

Posted: May 22, 2012 in Techilla

Inheritance vs Aggregation/ Composition vs Inheritance/ Is-a or Has-a ? Call it by any name, but this quandary is something which has baffled many design studies.
The other day I was designing some POC with Hibernate, and I got bitten by the performance bug. Having prior experience with Hibernate, I know what a beast it can be in terms of performance especially with complex inheritance mappings or associations .

As is often the case with me, one thing led to another and I veered down the Google way 🙂 . To paraphrase many eminent people, who have pretty much pushed me towards aggregation,let me provide a gist below:

An inheritance can always be rewritten as an association as follows

instead of


public class A {}
public class B extends A {}

we can use

public class B {
private A a;
}

We should use aggregation if part of the interface(available methods for us to override) is not used or has to be changed to avoid an illogical situation.

We only need to use inheritance, if we need almost all of the functionality without major changes. And when in doubt,we should always use Aggregation.
Also another line of thought was :
1.Whatever design strategy you choose, your choice will likely be the wrong one at some point because of changing requirements
2.Changing that choice is difficult once you’ve made it.
3.Inheritance tends to be a worse choice as it’s more constraining and hence we should go for aggregation.

To quote a discussion between Bill Venners and Erich Gamma  at:

Bill Venners: That extra flexibility of composition over inheritance is what I’ve observed, and it’s something I’ve always had difficulty explaining. That’s what I was hoping you could capture in words. Why? What is really going on? Where does the increased flexibility really come from?

Erich Gamma: We call this black box reuse. You have a container, and you plug in some smaller objects. These smaller objects configure the container and customize the behavior of the container. This is possible since the container delegates some behavior to the smaller thing. In the end you get customization by configuration. This provides you with both flexibility and reuse opportunities for the smaller things. That’s powerful. Rather than giving you a lengthy explanation, let me just point you to the Strategypattern. It is my prototypical example for the flexibility of composition over inheritance. The increased flexibility comes from the fact that you can plug-in different strategy objects and, moreovers, that you can even change the strategy objects dynamically at run-time.

Bill Venners: So if I were to use inheritance…

Erich Gamma: You can’t do this mix and match of strategy objects. In particular you cannot do it dynamically at run-time.

So, the writing’s on the wall for me. Choose aggregation over inheritance whenever you can, and hopefully, you will live to design another project before they find out that the design strategy implemented needs to be changed. 🙂

All info above are drawn from inheritance-vs-aggregation
and “Design principle” so all credit goes to original authors and I just summarized it above.

Logging a Spring +Hibernate application is especially useful during the initial stages when you would want to see whether all Hibernate configurations are fine. It might also be useful at the later stages to look at the query log generated to do some optimization. However, logging of combined Spring and Hibernate related data onto the same log file is not very straightforward (until you read this post, that is :). Its primarily because Spring and Hibernate use different logging technologies

Spring uses Jakarta Commons Logging API (JCL) which is mandatory to be in the classpath or the application context doesn’t get loaded.

Hibernate 3.3+ uses SL4J or Simple Logging Façade for Java

I have always used log4j to have a common logging repository for our application,

Now, for all these to work together and post everything onto the log file, we need the following libraries in our classpath:

  • commons-logging-1.1.1.jar
  • log4j-1.2.13.jar
  • slf4j-api-1.6.1.jar
  • slf4j-log4j12-1.6.4.jar

The last jar is the bridge between SL4J and log4j, however note that sl4j-log4j* and sl4j-jdk* cannot remain on the classpath at the same time, or they cause binding issues, so look out for that.(Will print on the logs if you have any such binding issues)

Finally, our log4j.xml which will contain the logging info.

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/"
	debug="false">

	<appender name="CONSOLE" class="org.apache.log4j.ConsoleAppender">
		<layout class="org.apache.log4j.PatternLayout">
			<param name="ConversionPattern" value="[%d{dd/MM/yy hh:mm:ss:sss z}] %5p %c{2}: %m%n" />
		</layout>
	</appender>

	<appender name="ASYNC" class="org.apache.log4j.AsyncAppender">
		<appender-ref ref="CONSOLE" />
		<appender-ref ref="FILE" />
	</appender>

	<appender name="FILE" class="org.apache.log4j.RollingFileAppender">

		<param name="File" value="C:/log/spring-hib.log" />
		<param name="MaxBackupIndex" value="100" />

		<layout class="org.apache.log4j.PatternLayout">
			<param name="ConversionPattern" value="[%d{dd/MM/yy hh:mm:ss:sss z}] %5p %c{2}: %m%n" />
		</layout>

	</appender>

	<category name="org.hibernate">
		<priority value="DEBUG" />
	</category>

	<category name="java.sql">
		<priority value="debug" />
	</category>

	<root>
		<priority value="INFO" />
		<appender-ref ref="FILE" />
	</root>

</log4j:configuration>

Note : org.hibernate will show the full blown list of boiler plate stuff , so it might be worthwhile to trim down to org.hibernate.SQL.

Also, if u put hibernate.show_sql=true in your configuration file, it will print the sql statement in the console as well.

There is a very nice pictorial representation here which shows the various binding among different loggers and it pointed me in the right direction, thanks Espen!:)

Uploading a file or an image and retrieving it is an extremely frequent activity and doing so via Mybatis/Spring must be a breeze as there are so many users who must be doing it!

So I thought, 6 hours before I started to code it. Unfortunately , Mybatis user manual has zero references to blob/clob insert /delete and searching on Google didn’t seem to go very far. There were pointers but no complete code examples. In the end, it proved to be exceedingly simple and I went to sleep a happy man. Here’s the full example to save half a day for somebody else.

Mybatis version : mybatis-3.1.0
Spring version : 3.1.1
Mybatis-Spring bundle : 1.1.1
Database : Oracle 10.2.0.4
Reqd. libs : commons-fileupload-*.jar , commons-io*.jar , ojdbc14.jar and obviously the reqd. spring and mybatis jars.

Database columns in EMPLOYEE table:

FILENAME VARCHAR2 (100 Byte),
FILECONTENTTYPE VARCHAR2 (100 Byte),
FILEDATA BLOB.

The actual file data is stored in a BLOB field.

Note: not a CLOB field, as we are mainly trying to host images here.(Even if some other file type is uploaded, it being stored as a BLOB will help to retrieve it exactly as it was stored, without any character encoding being applied, as in case of CLOB)

We are having a Spring MVC application, so we will augment our web-config.xml or whatever config file the DispatcherServlet listens to with the below code:


<bean id="multipartResolver"
    class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
	<property name="maxUploadSize">
		<value>10000000</value>
	</property>
</bean>

The fileupload size is in Bytes.

Model object / Form data

@Alias(value="emp")
public class Employee {
       private CommonsMultipartFile fileData;
       private byte[] fileDataBytes;
       private String fileName;
       private String fileContentType;
       //getters/setters
}

Our jsp will host the below :

spring form file upload

If we don’t put the enctype=”multipart/form-data, we will not be able to typecast the uploaded file into the CommonsMultiPartFile and hence we will not be able to retrieve the contentType and the filename. If we don’t put the encType, we can always retrieve the uploaded file as byte[] but in order to retrieve the file, we will have to store the contenttype as well, so an easier option is to use CommonsMultiPartFile.

Store or Upload the file or image in Mybatis


<update id="updateEmployee" parameterType="com.spring.model.Employee">
	update employee
	<set>
<if test="fileData.originalFilename != null">filename = #{fileData.originalFilename,jdbcType=VARCHAR},</if>
		<if test="fileData.ContentType != null">fileContentType =					#{fileData.contentType,jdbcType=VARCHAR},</if>
		<if test="fileData.bytes != null">fileData = 							#{fileData.bytes},
</if>
	</set>
	where
	empId = #{empId}
</update>

Note, that we don’t set the jdbcType of contentType, nor do we use any typehandlers as many suggested.

Also, note that we use the original CommonsMultipart object to retrieve the fileContentType,filename and fileData.

That’s it for storing the file.

Retrieve the uploaded file/image using Mybatis

Now, for retrieving it back, we will use the below query:

<select id="getUploadedFileForEmployee" parameterType="Long"
		resultType="emp">
		select empId,fileName,fileContentType,fileData as
		fileDataBytes
		from
		employee where
		empId=#{empId}

</select>

That’s it. We have successfully retrieved the file along with its name and contenttype. Now, we shall see how we can display it / download the file.

@Controller
public class EmployeeController {
	@Autowired
	private EmployeeBaseService employeeService;
	@Autowired
	private UploadedObjectView uploadedObjectView;
	public EmployeeBaseService getEmployeeService() {
		return employeeService;
	}
     //getters,setters
         @RequestMapping(value="/employeeDownloadFile")
	public ModelAndView downloadFile(@RequestParam("empId") long empId){
		Map model = new HashMap();
		Employee empMap = employeeService.getUploadedFileForEmployee(empId);
		model.put("data", empMap.getFileDataBytes());
		model.put("contentType", empMap.getFileContentType());
		model.put("filename", empMap.getFileName());
		return new ModelAndView(uploadedObjectView, model);
	}

For the save of the employee along with its data and a detailed explanation of the annotations, please refer here.

Ok, so we are done with our controller, but since the file to be downloaded can be of different types, so we construct a generic UploadedObjectView and populate it with the file data.

public class UploadedObjectView extends AbstractView {
	//To rediect to another page, with inline text.
	protected void renderMergedOutputModel1(Map model,
			HttpServletRequest request, HttpServletResponse response) throws Exception {
		  byte[] bytes = (byte[]) model.get("data");
	      String contentType = (String) model.get("contentType");
	      response.setContentType(contentType);
	      response.setContentLength(bytes.length);
	      ServletOutputStream out = response.getOutputStream();
	      out.write(bytes);
	      out.flush();
	}
	//For a download option
	@Override
	protected void renderMergedOutputModel(Map model,
			HttpServletRequest request, HttpServletResponse response) throws Exception {
		byte[] bytes = (byte[]) model.get("data");
		String contentType = (String) model.get("contentType");
		response.addHeader("Content-disposition","attachment; filename="+model.get("filename"));
		response.setContentType(contentType);
		response.setContentLength(bytes.length);
		ServletOutputStream out = response.getOutputStream();
		out.write(bytes);
		out.flush();
	}
}

We have 2 methods above:

If we override with the 1st method, the output will be redirected to another page with an inline text / image.

For a totally generic implementation, the overridden method 2 is safer as it provides with a download option.

That’s it folks :)! I hope this could be a help to somebody.

One common error which I have encountered in Mybatis while uploading large files was :

SQL state [72000]; error code [1013]; ORA-03111: break received on communication channel

This error is due to the query timeout being exceeded.

From the mybatis-config.xml(more info here), changed the value from 10 to 100 to resolve this issue.

<setting name="defaultStatementTimeout" value="100" />

Great post here by Juergen Hoeller if you need further inputs or just anything about Spring in particular. Thanks Juergen!

Goal of this session

  • Mybatis Mapper xmls and interfaces creation
  • Mybatis MapperFactoryBean to retrieve Mybatis SqlSessions which are threadsafe.
  • Mybatis MapperScannerConfigurer to automatically wire the mapper interfaces
  • Mybatis SqlSessionDaoSupport and SqlSessionTemplate
  • Spring Annotated Controllers
  • Spring example of get, post methods to retrieve and update an object.

Ok, so we have done our configurational changes here.

We have created our datasource, sqlsessionfactorybean, mybatis configurational file and referred to our mybatis mapper xmls.But we haven’t yet created the model object or the mapper xmls.

Step 1:  Model Object Creation : We will create the Employee object first.

public class Employee {
	protected long empId;
	protected String firstname;
	protected String lastname;
	protected String email;
	protected String telephone;
	protected String birthday;

          // we will see these properties later
	private CommonsMultipartFile fileData;
	private byte[] fileDataBytes;
	private String fileName;
	private String fileContentType;
          //getters and setters for all attributes.
	}

Step 2: Creating the Mybatis interfaces and mapper xmls.

Lets start with the interfaces. We had 2 interfaces BaseMapperInterface and EmployeeMapperInterface. Of these, BaseMapperInterface is a marker interface.

We will go straight to the EmployeeMapperInterface. There are multiple ways to do it, so I will show the legacy way first.

package com.mybatis.dao;
public interface EmployeeMapperInterface extends BaseMapperInterface{
public List getEmployeeWithId(Long id);
public int insertEmployee(Employee e);
public int updateEmployee(Employee e);
public void deleteEmployee(Long id);
//other data access methods.
}

Now, we will define the EmployeeMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.mybatis.dao.EmployeeMapperInterface">
<select id="getEmployeeWithId" parameterType="Long" resultType="emp">
		select empId,firstname,lastname,emailId as email,birthday,fileName from
		employee where
		1=1
		<if test="_parameter != null">
			AND empId=#{empId}
		</if>
		order by empId
	</select>
<insert id="insertEmployee" parameterType="com.spring.model.Employee">
		<!--
			the interface returns int, not long otherwise typecast errors were
			thrown
		-->
		<selectKey keyProperty="empId" resultType="Long" order="BEFORE">
			select Hibernate_Sequence.nextval as empId from dual
  		</selectKey>

		insert into employee(empId,firstname,lastname,emailId,filename,fileContentType,fileData )
		values(#{empId},#{firstname},#{lastname},#{email},#{fileData.originalFilename,jdbcType=VARCHAR},
			#{fileData.contentType,jdbcType=VARCHAR},#{fileData.bytes} )

	</insert>

   <update id="updateEmployee" parameterType="com.spring.model.Employee">
		update employee
		<set>
			<if test="firstname != null">firstname= #{firstname,jdbcType=VARCHAR},</if>
			<if test="lastname != null">lastname =#{lastname,jdbcType=VARCHAR},</if>
			<if test="email != null">emailid = #{email,jdbcType=VARCHAR},</if>
			<if test="fileData.originalFilename != null">filename = #{fileData.originalFilename,jdbcType=VARCHAR},</if>
			<if test="fileData.ContentType != null">fileContentType =	#{fileData.contentType,jdbcType=VARCHAR},</if>
			<if test="fileData.bytes != null">fileData = #{fileData.bytes},</if>
		</set>
		where
		empId = #{empId}
	</update>

	<delete id="deleteEmployee" parameterType="Long">
		delete from employee
		where empId = #{empId}
	</delete>

Now, if you see the above xml, you would see a select, insert , update and delete tags. Don’t worry, we would go through each of them later in this tutorial. For now, we shall see the implementation of this interface.

Step 3 : Legacy way of defining the implementation of the interface.
Remember MapperFactoryBean on the 1st post? Its not required if we follow this legacy approach and the changed mapper-config.xml will look like below

<bean id="employeeMapper" class ="com.mybatis.dao.EmployeeMapperImpl">
   <property name="sqlSessionFactory" ref="sqlSessionFactory" />
</bean>

Obviously we should still follow the inheritance strategy as defined earlier and this referring of sqlSessionFactory directly by employeeMapper is just for demonstration purposes.

I say this legacy because with MapperFactoryBean this is no longer required. We can work only with the interfaces. However, life is not always so beautiful and we have to look at old code in order to debug , maintain or improve.


public class EmployeeMapperImpl extends SqlSessionDaoSupport implements EmployeeMapperInterface{

	@Override
	public void deleteEmployee(Long id) {
		getSqlSession().delete("com.mybatis.dao.EmployeeMapperInterface.deleteEmployee", id);
	}

	@Override
	public List<Employee> getEmployeeWithId(Long id) {
		return getSqlSession().selectList("com.mybatis.dao.EmployeeMapperInterface.getEmployeeWithId", id);

	}

	@Override
	public int insertEmployee(Employee e) {
		return getSqlSession().insert("com.mybatis.dao.EmployeeMapperInterface.insertEmployee", e);	}

	@Override
	public int updateEmployee(Employee e) {
		SqlSessionTemplate tm= (SqlSessionTemplate) getSqlSession();
		int id = tm.update("com.mybatis.dao.EmployeeMapperInterface.updateEmployee", e);
		//getSqlSession().rollback();
		return id;
	}
}

Now, before we start explaining, we would slightly veer off from the MVC pattern and we shall look at how a standalone Mybatis application would work . For a detailed explanation, please visit here.

At the core of all Mybatis stuff, is an SqlSessionFactory which opens and closes SqlSession. SqlSession is not thread safe and needs to be aligned with the HttpRequest cycle in case of a web application.

 For Spring Mybatis, there are 3 ways to retrieve the sessions :

i. extend SqlSessionDaoSupport as we are doing above and retrieve the session using getSqlSession(). This method returns a thread-safe SqlSession which we can use in our Spring transactions. Then, this session can be used to perform insert/update/delete/selectOne/selectList operations.

ii. We can also use SqlSessionTemplate. We can instantiate it in the database-config.xml

<bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate">
 <constructor-arg index="0" ref="sqlSessionFactory" />
</bean>

As can be seen above, it can also be instantiated by using the sqlSessionFactory.

SqlSession sqlSsession = new SqlSessionTemplate(sqlSessionFactory);

To summarize, SqlSessionTemplate should always be used instead of SqlSession because the base MyBatis SqlSession cannot participate in Spring transactions and is not thread safe. Switching between the two classes in the same application can cause data integrity issues.
Also, in step i. when we do getSqlSession, we actually retrieve SqlSessionTemplate, so the below statement would work fine.

SqlSessionTemplate tm= (SqlSessionTemplate) getSqlSession();

iii.  Finally the MapperFactoryBean
Instead of using SqlSessionDaoSupport or SqlSessionTemplate directly from the DAOs, we can use MapperFactoryBean to inject interface DAOs into our service classes.


<bean id="baseMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
	<property name="mapperInterface" 									value="com.mybatis.dao.BaseMapperInterface" />
	<property name="sqlSessionFactory" ref="sqlSessionFactory" />
</bean>

<bean id="employeeMapper" parent="baseMapper">
<property name="mapperInterface" value="com.mybatis.dao.EmployeeMapperInterface" />
</bean>

The MapperFactoryBean handles creating an SqlSession as well as closing it. If there is a Spring transaction in progress, the session will also be committed or rolled back when the transaction completes. Finally, any exceptions will be translated into Spring DataAccessExceptions.

MapperScannerConfigurer and automatically marking the interfaces

Finally, those of you who don’t want to spend lots of time in wiring down each and every interface bean, can use the MapperScannerConfigurer which allows you to automatically scan the directories and mark the mapper interfaces.
1. Define the MapperScannerConfigurer and mark the basePackage.


<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
     <property name="basePackage" value="org.mybatis.spring.sample.mapper" />
</bean>

2. The mapper interfaces which are referred in the service classes need to be autowired, since their references will no longer be present in the mapper-config.xml

3. Finally, sqlSessionFactory also needs to be configured(contrary to the Mybatis manual), else the mappers will not work and will throw this exception :

org.springframework.beans.factory.BeanCreationException: Error creating bean with name ’employeeMapperInterface’ defined in file [C:\anirban\Work_Ani\SpringIntegration\WebRoot\WEB-INF\classes\com\mybatis\dao\EmployeeMapperInterface.class]: Invocation of init method failed; nested exception is java.lang.IllegalArgumentException: Property ‘sqlSessionFactory’ or ‘sqlSessionTemplate’ are required

Note: There was an issue with PropertyPlaceHolderConfigurer not working when used in conjunction with mybatis-spring-3.1.0. Its resolved by replacing with mybatis-spring-3.1.1 bundle.

Thats it folks for the Mybatis stuff for this session. Now, lets jump to the Spring related changes . Recall that ,                                                                                             

 Request –> Spring MVC controller –> accesses Service facade –> accesses the DAO xml/interface.

We are done with the last leg(DAO xml/interface) and we will now construct the Service facade.
As always to encourage good coding practices, we will create an interface for the EmployeeService.

public interface EmployeeBaseService {
	public Employee getEmployeeById(long empId);
	public long saveEmployee(Employee employee) throws Exception;
	public void deleteEmployee(long empId);

}

Now, the actual implementation of the service:

@Service
public class EmployeeService implements EmployeeBaseService{

	@Autowired
	EmployeeMapperInterface employeeMapper;
         //getters, setters
         @Override
	public Employee getEmployeeById(long empId){
		//retrieve from database
		List empList = employeeMapper.getEmployeeWithId(empId);
		if(empList != null && empList.size()>0){
			return (Employee) empList.get(0);
		}
		return null;

	}

	@Override
	public long saveEmployee(Employee employee){
		long empId = 0l;
		if(employee.getEmpId()==0){
			empId  = new Long( employeeMapper.insertEmployee(employee));
		}else{
			 employeeMapper.updateEmployee(employee);
			 empId  =  employee.getEmpId();
		}
		return empId;
	}

	@Override
	public void deleteEmployee(long empId) {
		employeeMapper.deleteEmployee(empId);

	}

Annotated Employee Controller

@Controller
public class EmployeeController {
	@Autowired
	private EmployeeBaseService employeeService;

          @RequestMapping(value = "/employeeHome",method=RequestMethod.GET)
	public String displayHomePage(@RequestParam("empId") long empId,ModelMap m){
		System.out.println("employeeHome>> "+empId);
		//retrieve the employee with this id.
		Employee employee = null;
		Employee empMap = employeeService.getEmployeeByIdMap(empId);
		if(empId ==0){
			employee = new Employee();
		}else{
			employee = employeeService.getEmployeeById(empId);

		}
		m.addAttribute("employee",employee);
		System.out.println(employee);
		return ProjectConstants.SECURE_FOLDER+"employeeHome";
	}
         @RequestMapping(value="/employeeEdit",method=RequestMethod.POST)
	public String saveEmployee(@ModelAttribute("employee")
                Employee emp,  BindingResult br) throws Exception{
		if(br.hasErrors()){
			return "employeeHome";
		}
		System.out.println(emp);

		employeeService.saveEmployee(emp);
		return "redirect:employeeHome.html?empId="+emp.getEmpId();
	}

Ok, lets go over it. The controller contains a reference to the EmployeeBaseService and this is autowired.
First the displayHomePage() which is accessed via a GET.

 

Points to note :

1. @RequestParam(“”) is used to bind a request parameter to a method parameter.  If a RequestParam is specified, it becomes mandatory for the URI to contain it.Else, can  be used as @RequestParam(value=””,required=false)

2.  This method has a signature :                                                                                              String * (@RequestParam(“<param>”) datatype method-arg,ModelMap model)

3.  ModelMap.addAttribute(“paramName”,<param>). This paramName is important. As it has to be set in the view as the modelattribute, else the jsp will not be rendered and the following exception will come:
Neither BindingResult nor plain target object for bean name ‘command’ available as request attribute
4.  Returns the viewname , so essentially there would be a employeeHome.jsp lying around under ProjectConstants.SECURE_FOLDER.

5. @RequestMapping(value = “/employeeHome”,method=RequestMethod.GET) means this method would be invoked when we have a call like :
http://localhost:8080/springProj/employeeHome.html?empId=92178033
Note : the request parameter being passed.

Next, the saveEmployee() which is accessed via the POST.

  1. Annotation @ModelAttribute as the method parameter. This is used to retrieve the command object, after filling out the form.
  2. Returns a redirect to the url which is going to be picked up the get method, the redirect prevents an accidental re-update upon refreshing the screen.
  3.  @RequestMapping(value=”/employeeEdit”,method=RequestMethod.POST) will invoke this method, meaning there must be a form whose action would point to employeeEdit.html

Finally, lets complete this tutorial by showing the view (*. jsp) which will render the model.

Spring ModelAttribute JSP

Features to be noted in this jsp:

  1. modelAttribute “emp” is necessary as mentioned earlier.
  2. <form:form method=”post” action=”employeeEdit.html”  , so basically this will look like an employee personal details update form where the employee is redirected to his/her view page after the update.

 

Right that’s it.