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package org.glassfish.appclient.server.core.jws.servedcontent;
import java.util.LinkedList;
import java.util.Properties;
import org.glassfish.appclient.server.core.jws.Util;
import org.glassfish.appclient.server.core.jws.servedcontent.DynamicContent.InstanceAdapter;
/**
*
* @author tjquinn
*/
/**
*Represents dynamic content in template form.
*
*This class also keeps track of the most recent times the object's template
*was used to generate content that was different from the result of the
*previous generation using this template. This
*information is used in responding to HTTP HEAD requests. Java Web Start uses
*HEAD requests to find out if a document on the server is more recent than
*the locally cached copy on the client. If so, then Java Web Start will
*request the updated version with a routine GET request.
*
*To avoid incorrectly reporting obsolete cached documents as current, this
*class keeps track of when the content generated by the template is different
*from the previous generation.
*
*The generated content can depend on request-time information
*(such as command line arguments passed in the query string of the HTTP request).
*We save and track only a few individual response instances, because the assumption
*is that requests that carry query strings (which are converted into command line
*arguments passed to ACC and on through to the app client) are likely to change
*frequently and not necessarily be reused often. Keeping a few allows caching
*the different content resulting from a small number of different argument
*value settings, but avoids the problems of caching every single response
*which could become a large memory drain if each request specified a
*different set of arguments (for instance, one of the arguments could be a
*timestamp that would change every time).
*/
public class CachingDynamicContentImpl extends Content.Adapter implements DynamicContent {
/** maximum number of instances of content to keep for each template */
private static final int DEFAULT_MAX_INSTANCES = 4;
/**
*the template which will be used at runtime to create the actual response
*to the HTTP request
*/
private final String template;
/** the MIME type of the data represented by this CachingDynamicContentImpl instance */
protected final String mimeType;
/** content instances resulting from previous HTTP GET requests */
private final LinkedList instances = new LinkedList();
/** max. number of instances to cache */
private final int maxInstances;
/**
* Returns a new instance of CachingDynamicContentImpl.
* @param origin the ContentOrigin for the new content instance
* @param contentKey the content key used to store and retrieve the content
* @param path the path relative to the subcategory in which this document is addressable
* @param mimeType the MIME type of data represented by the content generated by this
* object.
* @return new CachingDynamicContentImpl object
*/
public CachingDynamicContentImpl(final String template, final String mimeType) {
this(template, mimeType, DEFAULT_MAX_INSTANCES);
}
public CachingDynamicContentImpl(final String template, final String mimeType,
final int maxInstances) {
this.template = template;
this.mimeType = mimeType;
this.maxInstances = maxInstances;
}
/**
* Returns the CachingDynamicContentImpl.InstanceImpl for this template corresponding to
* the specified substitution token values.
* @param tokenValues the name/value pairs to be substituted in the template
* @param createIfAbsent selects whether a new CachingDynamicContentImpl.InstanceImpl should
* be created for the resulting text if the content text resulting from the
* substitution is not already cached by this CachingDynamicContentImpl.
* @return the instance corresponding to the content generated by the tokenValues;
* null if no such instance already exists for this CachingDynamicContentImpl and createIfAbsent
* was false.
*/
public Instance getExistingInstance(final Properties tokenValues) {
return getOrCreateInstance(tokenValues, false);
}
public Instance getOrCreateInstance(final Properties tokenValues) {
return getOrCreateInstance(tokenValues, true);
}
@Override
public boolean isMain() {
return false;
}
private Instance getOrCreateInstance(final Properties tokenValues, final boolean createIfAbsent) {
/*
* I generally avoid passing in flags to control the inner flow of a
* method, but in this case we want the search and the optional addition
* to take place atomically inside the synchronized block. This way
* the synchronized clause is in one place.
*/
final String textWithPlaceholdersReplaced =
Util.replaceTokens(template, tokenValues);
/*
* Look for an instance with its text matching the just-computed
* replacement text.
*/
Instance result = null;
synchronized (instances) {
for (Instance i : instances) {
if (i.getText().equals(textWithPlaceholdersReplaced)) {
return i;
}
}
if (createIfAbsent) {
result = new InstanceAdapter(textWithPlaceholdersReplaced);
addInstance(result);
}
}
return result;
}
/**
* Adds a new content instance to this dynamic content. If adding the instance
* makes the cache too long, discards the oldest instance.
* @param newInstance the new instance to be added to the cache
*/
private void addInstance(final Instance newInstance) {
synchronized (instances) {
instances.addFirst(newInstance);
if (instances.size() > maxInstances) {
instances.removeLast();
}
}
}
/**
* Returns the MIME type associated with this content.
* @return the MIME type for this content
*/
public String getMimeType() {
return mimeType;
}
/**
* Clears the cached instances.
*/
protected void clearInstances() {
instances.clear();
}
/**
* Returns a string representation of the CachingDynamicContentImpl.
*/
@Override
public String toString() {
return super.toString() + ", template=" + template + ", MIME type=" + mimeType;// + ", most recent change in generated content=" + timestamp;
}
@Override
public boolean equals(Object obj) {
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final CachingDynamicContentImpl other = (CachingDynamicContentImpl) obj;
if ((this.template == null) ? (other.template != null) : !this.template.equals(other.template)) {
return false;
}
if ((this.mimeType == null) ? (other.mimeType != null) : !this.mimeType.equals(other.mimeType)) {
return false;
}
if (this.maxInstances != other.maxInstances) {
return false;
}
return true;
}
@Override
public int hashCode() {
int hash = 7;
hash = 89 * hash + (this.template != null ? this.template.hashCode() : 0);
hash = 89 * hash + (this.mimeType != null ? this.mimeType.hashCode() : 0);
hash = 89 * hash + this.maxInstances;
return hash;
}
}