File change listener
Hi !
My java app runs in an endless polling loop (by design) interrogating approx. 100 external devices via a comm port.
This endless loop is interrupted when any keyboard entry is made, processed, then loop is again allowed to resume.
I now need to interrupt my app if a certain file is changed(ie: a new line record is added).
.... then to copy this file into my app for processing, then continue my normal loop polling.
I think I need to add a "file listener" to this target file , but I'm new to Java.
Can some one suggest a code snip to get me started?
Thanks!
I now need to interrupt my app if a certain file is changed(ie: a new line record is added)..... then to copy this file into my app for processing, then continue my normal loop polling.
Java doen't provide a file change notifier. Read the "certain file" for a file parameter (maybe last modified) and if it's different from the previous read, do what is wanted. Depending on the specifics of your situation, you may want to do this in a separate thread from your polling.
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Value change listener method on h:selectBooleanCheckbox in h:dataTable
Hello,
Does JSF handle value change listeners as expected when they are attached to h:selectBooleanCheckbox components within an h:dataTable?
In the following example, I have a JSP that has some h:selectBooleanCheckbox components nested in an h:dataTable, and some that aren't. When I bulid and deploy the example to Tomcat 5.5, I can see (using the log4j output) that the value change listener methods for the checkboxes that are NOT in the dataTable are fired, but the ones that are in the dataTable do not get fired.
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----------------------------- JSP:
<%@ page language="java" %>
<%@ taglib uri="http://java.sun.com/jsf/html" prefix="h" %>
<%@ taglib uri="http://java.sun.com/jsf/core" prefix="f" %>
<f:view>
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<h:column>
<h:outputText value="#{thisBean.id}: " />
</h:column>
<h:column>
<h:selectBooleanCheckbox value="#{thisBean.checked}" valueChangeListener="#{checkboxBean.somethingChanged}" />
</h:column>
</h:dataTable>
<h:panelGrid columns="2">
<h:outputText value="One:"/>
<h:selectBooleanCheckbox id="firstOne" valueChangeListener="#{checkboxBean.somethingChanged}" />
<h:outputText value="Two:"/>
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<h:panelGroup/>
<h:commandButton value="Do Stuff" action="#{checkboxBean.doStuff}" />
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</h:form>
</f:view>----------------------------- Beans:
package workshop;
import javax.faces.event.ValueChangeEvent;
import org.apache.log4j.Logger;
* Test attaching value change listener methods to checkboxes.
public class CheckboxBean {
private static final Logger logger = Logger.getLogger(CheckboxBean.class);
private SomeBean[] beans = null;
public CheckboxBean() {
logger.debug("CheckboxBean()");
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SomeBean[] someBeans = new SomeBean[3];
someBeans[0] = new SomeBean("firstGuy", false);
someBeans[1] = new SomeBean("2ndGuy", false);
someBeans[2] = new SomeBean("third", false);
this.setBeans(someBeans);
return null;
public String doStuff() {
logger.debug("doStuff()");
return this.load();
public void somethingChanged(ValueChangeEvent e) {
logger.debug("somethingChanged() in component with id " + e.getComponent().getId() );
public SomeBean[] getBeans() {
logger.debug("getBeans()");
return this.beans;
public void setBeans(SomeBean[] beans) {
logger.debug("setBeans()");
this.beans = beans;
package workshop;
public class SomeBean {
private boolean checked = false;
private String id = null;
public SomeBean() {
public SomeBean(String anId, boolean bool) {
super();
this.id = anId;
this.checked = bool;
public String getId() {
return this.id;
public void setId(String id) {
this.id = id;
public boolean isChecked() {
return this.checked;
public boolean getChecked() {
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}----------------------------- faces-config.xml:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE faces-config PUBLIC "-//Sun Microsystems, Inc.//DTD JavaServer Faces Config 1.1//EN" "http://java.sun.com/dtd/web-facesconfig_1_1.dtd">
<faces-config>
<managed-bean>
<description>Checkbox bean.</description>
<managed-bean-name>checkboxBean</managed-bean-name>
<managed-bean-class>workshop.CheckboxBean</managed-bean-class>
<managed-bean-scope>request</managed-bean-scope>
</managed-bean>
</faces-config>----------------------------- log4j config:
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
<appender name="RollingFile" class="org.apache.log4j.RollingFileAppender" >
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<param name="Append" value="false"/>
<param name="MaxFileSize" value="4096KB" />
<param name="MaxBackupIndex" value="4" />
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<param name="ConversionPattern" value="%d{DATE} %-5p %-15c{1} : %m%n"/>
</layout>
</appender>
<category name="workshop" >
<priority value="debug" />
</category>
<root>
<priority value="warn" />
<appender-ref ref="RollingFile" />
</root>
</log4j:configuration>I have Just run into the same problem. When using the following code inside a data table the valueChangeListener event is not fired when the checkbox has it's value changed. Is this a bug?
I created a simple page with just a form and the selectBooleanCheckbox. This time the valueChangeListener event fired OK. It seems the problem only occurs when the check box is inside the dataTable
here is the code snippet
<h:form >
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What is the best way to implement a 'fileListener'?
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