The file “beans.xml” used for you application is already a kind of configuration file. However, this file is designed for the developer who can quickly customize the application with less coding changes. It is not recommended for an end user to change the file.

For example, you can, of course, define the database connection properties in the beans.xml file straight away. This way, every time a user wants the application to connect to a database at a different location, the beans.xml file needs to be modified. For a complicated application, the file can grow very complicated as well. Therefore, making changes to the beans.xml file directly may not seem obvious to the end user.

Fortunately, Spring have already come up with a solution for this problem. You can define the properties in the “beans.xml” file with place holders and use the Spring provided bean PropertyPlaceholderConfigurer to replace the place holders with the value from a properties file. Here is an example of the use of PropertyPlaceholderConfigurer.

In the example from the above link, it specifies one location for the properties file with a classpath: “classpath:com/foo/jdbc.properties”. In addition to that, you can also specify a file on your file system. When using a file on file system, remember to add “file:/” to an absolute path; otherwise, Spring will treat it as a relative path even the value starts with “/”.

PropertyPlaceholderConfigurer also allows you to define some default values using the property “properties“. The following is an example of using the default values if the file defined by “locations” property does not exist. Please note setting “ignoreResourceNotFound” to true is necessary. If not set, the application will throw exception if the defined property does not exist even we’ve defined the default values.

<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
  <property name="ignoreResourceNotFound" value="true" />
  <property name="locations">
    <value>file:///etc/app/jdbc.properties</value>
  </property>
  <property name="properties">
    <props>
      <prop key="jdbc.driverClassName">com.mysql.jdbc.Driver</prop>
      <prop key="jdbc.url">jdbc:mysql://localhost:3306/mytechtip</prop>
      <prop key="jdbc.username">jdbc_username</prop>
      <prop key="jdbc.password">xxx</prop>
    </props>
  </property>
 
</bean>
 
<bean id="dataSource" destroy-method="close" 
    class="org.apache.commons.dbcp.BasicDataSource">
  <property name="driverClassName" value="${jdbc.driverClassName}"/>
  <property name="url" value="${jdbc.url}"/>
  <property name="username" value="${jdbc.username}"/>
  <property name="password" value="${jdbc.password}"/>
</bean>

Java beans in Spring can also have their collection properties populated in the beans.xml file. The collection properties here mean things like List, Map and Array.

For example, if you want to create a JPA EntityManagerFactory with a set of connection properties, these properties can be configured in beans.xml like this:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xmlns:p="http://www.springframework.org/schema/p"
  xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
    <bean id="entityManagerFactoryCreator" 
    class="com.mytechtip.example.EntityManagerFactoryCreator">
    <property name="persistenceUnitName" value="HRMN_Repository"/>
    <property name="jpaProperties">
      <props>
        <prop key="openjpa.ConnectionURL">the_url</prop>
        <prop key="openjpa.ConnectionDriverName">the_driver_class_name</prop> 
        <prop key="openjpa.ConnectionUserName">the_user_name</prop>
        <prop key="openjpa.ConnectionPassword">the_password</prop>
      </props>
    </property>
  </bean>
</beans>

Here, jpaProperties in the actual java class “EntityManagerFactoryCreator” is an instance of Properties. And you can just use this properties to create EntityManagerFactory.

    // ...
    private Properties jpaProperties;
    //...
    public void setJpaProperties(Properties prop) {
        this.jpaProperties = prop;
    }
    // ...
    public EntityManagerFactory create() {
        return Persistence.createEntityManagerFactory("myPersistenceUnit", prop);
    }

Actually, Spring already have something similar for you to access EntityManagerFactory with ease. The beans used for the task are:

• org.springframework.orm.jpa.LocalEntityManagerFactoryBean
• org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean

More information / examples can be found here about the support of JPA entity manager factory creatation in Spring.

Spring is a very flexible java framework. In spring, beans are the main building bricks of an application while the bean configuration file (mostly beans.xml) acts as cement that glues the beans together.

The file beans.xml also allows beans to be initialized with particular values. For example, you can set the JDBC driver, user name, password for a java bean that is in charge of database connection in the beans.xml file as the following example.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:p="http://www.springframework.org/schema/p"
	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
 
	<bean id="dbManager" class="com.mytechtip.example.DbManager">
		<property name="jdbcDriver" value="com.mysql.jdbc.Driver"/>
		<property name="jdbcUrl" value="jdbc:mysql://localhost/app"/>
		<property name="jdbcUser" value="app" />
		<property name="jdbcPassword" value="app" />
	</bean>
</beans>

So in the java class “com.example.app.DbManager”, you can make JDBC connections with the fields/properties value set as in the beans.xml file. The DbManager class may look as simple as the following:

package com.mytechtip.example;
 
import java.sql.Connection;
import java.sql.DriverManager;
 
public class DbManager {
 
	private String jdbcDriver;
	private String jdbcUrl;
	private String jdbcUser;
	private String jdbcPassword;
 
	public String getJdbcDriver() {
		return jdbcDriver;
	}
	public void setJdbcDriver(String jdbcDriver) {
		this.jdbcDriver = jdbcDriver;
	}
 
        // more getters and setters ...
 
	public Connection getConnection() throws Exception {
             Class.forName (getJdbcDriver()).newInstance();
             return DriverManager.getConnection(
                   getJdbcUrl(), getJdbcUser(), getJdbcPassword());
	}
}

There is one note: These properties are set after the constructor of the bean is called. So if you try to make a JDBC connection in the constructor with the fields, you will mostly get exceptions.

Anyway, this is a very simple example of the bean configuration. We will show more examples to learn the flexibility of the bean configuration in Spring. ]]> http://robin.mytechtip.com/2010/05/18/how-to-configure-spring-beans-xml-file-basic-usage/feed/ 0 http://robin.mytechtip.com/2010/03/24/remember-to-clear-entity-manager-if-entities-no-longer-used/ http://robin.mytechtip.com/2010/03/24/remember-to-clear-entity-manager-if-entities-no-longer-used/#comments Wed, 24 Mar 2010 05:04:55 +0000 robin http://robin.mytechtip.com/?p=67 Recently  a lesson was learned about the proper use of Java JPA to persist a large number of records into database in a batch process.

Some times it is necessary to load the records line by line from a large file and insert into the database table. There can be several ways to do this:

• Use the database provided tool to load the data into table. It can be a special sql command or a special stored procedure. This method is quite database specific and not portable.
• Write the program to load the data into the database table (Using JDBC if the program is written in Java).  This method can be applied to different databases if the insert SQL statement conforms to a level of standard.
• Use JPA to persist the object one by one. This allows for changing database more easily (under the condition that the JPA provider supports the database.

We used the third options to load the records into the database as we want to support multiple databases without  low level tweaking. However, the first implementation seemed very slow compared with the second option. And it became slower and slower when process of persisting records  progressed.

After a few checking, we realized that we didn’t call the method “clear” of the class EntityManager each time we persisted the object.  The EntityManager kept managing these objects so the resource was not released immediately, making it become slower and slower.

Once we add the “clear” method call, the performance became acceptable. So lesson learned about the use of JPA.

Since version 1.6.1, Ant, the java build tool, has a core task called “cvschangelog“. It is quite useful to use this task to grab a list of recent changes committed to the CVS repository. The output of this task is in XML format. Something like the following:

<changelog>
<entry>
<date>2009-09-02</date>
<time>12:00</time>
<author>robin</author>
<file>
<name>test/ant/task/ChangeLog.txt</name>
<revision>1.2</revision>
<prevrevision>1.1</prevrevision>
</file>
<msg><![CDATA[A commit message]]></msg>
</entry>
<entry>
…
</entry>
…
</changelog>

To transform the xml formatted changelog into a human friendly html, you can do an XSL transformation with a XSL file. There is a default one in the Ant distribution, so you can use the following task to get a change log in html format.

<style in=”changelog.xml”
out=”changelog.html”
style=”${ant.home}/etc/changelog.xsl”>
<param name=”title” expression=”Ant ChangeLog”/>
<param name=”module” expression=”the_module”/>
<param name=”cvsweb” expression=”the_url”/>
</style>

The default generated html lists each commit change one by one. In some cases, we want to group the commit changes by dates. To do so, we have to change the default xsl file.

It seems that the new XSLT version 2.0 has specified a group functionality. However, it turns out only a few XSLT tools support this new feature. Fortunately, There is a way that allows us to do the grouping using XSLT version 1.0. By applying this method, we have the following looking xsl code for the HTML <BODY> part.

<body>
<h1>
<a name=”top”><xsl:value-of select=”$title”/></a>
</h1>
<p style=”text-align: right”>Designed for use with <a href=”http://ant.apache.org/”>Apache Ant</a>.</p>
<hr/>

<xsl:key name=”log-by-date” match=”entry” use=”date” />

<xsl:template match=”changelog”>
<xsl:for-each select=”entry[count(. | key('log-by-date', date)[1]) = 1]”>
<xsl:sort select=”date” order=”descending” />
<h2><xsl:value-of select=”date”/><xsl:text></xsl:text></h2>
<xsl:for-each select=”key(’log-by-date’, date)”>

<xsl:sort select=”time” order=”descending” />

<table border=”0″ width=”100%” cellspacing=”1″>
<tr>
<td class=”dateAndAuthor”>
<!– <xsl:value-of select=”date”/><xsl:text> </xsl:text> –>
<xsl:value-of select=”time”/><xsl:text> </xsl:text><xsl:value-of select=”author”/>
</td>
</tr>
<tr>
<td>
<pre><xsl:apply-templates select=”msg”/></pre>
<ul>
<xsl:apply-templates select=”file”/>
</ul>
</td>
</tr>
</table>
</xsl:for-each>
</xsl:for-each>
</xsl:template>

</body>

Use the above code to replace the <body> part in the original changelog.xsl file, then it  will allow you to group the change logs by date.

Google Web Toolkit (GWT) is a handy Ajax Web application development tool. Since version 1.6.4, GWT uses Jetty instead of Tomcat as the embedded Web application container.

However, when I installed GWT plugin (version 1.6.4) for Eclipse, the default generated web application used the version 2.3. So when i used expression language in the jsp pages, it didn’t evaluate. Something like “${title}” as the output in the hosted mode running on jetty. It should also be the same result even i deployed to a tomcat container, as the web app version is still 2.3. This is understandable, as Expression Language is part of JSP version 2.0 standard, which is bound with Servlet (Web App) version 2.4. So if you want to make the expression language work, make sure your web app is using 2.4 or higher.

However, while using version 2.4 works fine, i’ve got the same problem when i use version 2.5, which is hard to understand why. This problem seems only in Jetty, not in Tomcat. I don’t know if anyone else have encountered the same problem as I did, but the following link seems to explain the reason behind: http://docs.codehaus.org/display/JETTY/JSP+expression+do+not+evaluate

Apart from this problem (which can be worked around), the use of GWT plugin seems more convenient than the traditional web app development in eclipse.

It is often necessary to escape the special html code from the user input in case of avoiding cross site attack (XSS).

Initially i thought jdk provides a method somewhere to do this like function htmlentities() in php, but i failed to find it. All i found is a class called “URLEncoder ” which i don’t think can do this job.

I don’t want to reinvent the wheel as I believe there must be some java packages available that do this job. Googling “java encode html” didn’t lead me straight to the right java package (at least not the one I’d like to use).

After a while, I finally found one package i’d like to use. it’s from Apache Commons project, called “Commons Lang“. The method “StringEscapeUtils.escapeHtml(…) ” can do the encode job while the other method called unescapeHtml can do the decode job. So, I don’t have to write my own method…