Home > Articles > Programming > Java

Like this article? We recommend

A Common CCI architecture

In Part 1 of this essay, we quickly rejected Properties as a general purpose configuration mechanism. In this second part, we have seen that J2EE deployment descriptors and the Preferences API are both much better solutions. However, neither is perfect and the two are currently incompatible. In this section I will sketch the initial outline of a common CCI architecture. The design goals are as follows, in order of priority:

  1. Systematize support for structure, lookup, scope, and metadata.

  2. Preserve the advantages of J2EE deployment descriptors and the Preferences API.

  3. Pay as you go--the CCI infrastructure should be layered so that you only load the features that you need.

  4. Build nothing new--leverage existing code wherever possible.

  5. Integrate with existing code with minimal changes.

Note that this design is not intended as a final answer, but as a starting point for debate.

A first cut at a CCI design

1. Generalize the Preference API's notion of scope to hook in arbitrary providers. The Preferences API defines two scopes: system and root. In order to extend this to support arbitrary scopes, one could add a factory method with a String scope parameter. In this scheme, the new PreferencesFactory interface would look like this:

public interface PreferencesFactory {
public Preferences 
            systemRoot();
public Preferences userRoot();
public 
            Preferences root(String scope);
}

Scopes should be named using standard Java package naming conventions. Using this approach allows plugin providers to support legacy configuration schemes. The following table shows some possible scope names and their purposes

Table 1. Some possible preference scopes.

Scope Purpose
java.lang.util.prefs.User User scope from current Preferences API
java.lang.util.prefs.System System scope from current Preferences API
javax.servlet.Webapp accesses web.xml
javax.naming.Properties accesses the eccentric search path for jndi.properties files
javax.security.Properties accesses the security.properties file

The systemRoot and userRoot methods are no longer strictly necessary, but are retained for compatibility.

2. Make XML a first class citizen in the Preferences API. In the world of component configuration, both name/value pairs and XML documents are here to stay. The Preferences API already supports the former, and it would be simple to add methods to make XML a first class citizen as well:

package java.util.prefs;
import 
            org.w3c.dom.*;
public abstract class Preferences {
public 
            abstract String get(String key, String def);
public abstract 
            Document getDocument(String key, Document default);
public 
            abstract void put(String key, String value);
public abstract 
            Document putDocument(String key, Document 
            value);
//etc.
}

3. Explicitly permit some backing stores to be read-only. The Preferences API allows for programmatic write access to configuration. However, this will not make sense for all implementations. For example, consider JNDI properties. As you may remember from Part 1, JNDI properties have a long search path:

  • JAVA_HOME/lib/jndi.properties

  • any jndi.properties file visible to the current class loader

  • system properties, either passed on the command line or set using java.lang.System

  • properties explicitly passed to the InitialContext constructor

  • for Applets, properties set in AppletContext

  • provider resource files

If an application attempts to write JNDI properties using the Preferences API, it is unclear to which location the properties should be written. The simplest way to deal with this problem is to disallow write access when accessing JNDI properties through the legacy javax.naming.Properties scope.

There are two ways to implement this prohibition: either create a ReadOnlyStoreException subclass of BackingStoreException for providers that are read-only, or simply throw a BackingStoreException with an appropriate detail message.

4. Add metadata support to the Preferences API. None of the approaches to CCI that we have discussed thus far have any programmatic support for metadata. This is perhaps the single biggest weakness of CCIs in comparison with their better known cousins, APIs. To remedy this, the Preferences API should include a programmatic interface to enumerate CCI metadata, i.e. the possible configuration settings exposed by a package or class. Here is one possible approach:

package java.util.prefs;
public interface 
            PreferenceMetadata {
public Iterator getKeyNames(String 
            packageOrClass);
public Document getSchema(String keyName); 
            
}

The getKeyNames method returns an iterator over all the configuration settings that are used by a particular class or package. The getSchema method returns an XML schema that describes the values that a particular configuration setting can take. (Note that for backing stores that use simple primitive types instead of XML, getSchema still be used--the schema returned will just be trivial.)

It is easy to design the PreferenceMetadata interface. The hard question is "Where will this information come from?" There are four reasonably obvious ways to discover this information:

  1. A tool could analyze the bytecodes of compiled classes to locate calls into the Preferences API, and infer most of this information from the method calls used. This is ideal in the sense that the metadata will by definition always be in sync with the code. The disadvantage is having to write the tool.

  2. Store configuration metadata in a well-known file inside a JAR file. This requires that a developer generate and maintain the metadata, and that code always be deployed in JARs.

  3. Store configuration metadata using the new Custom Attributes in Java Specification (JSR 175). This is very similar to the previous option except code no longer needs to be deployed in JARs. On the other hand this approach depends on a cool new technology that doesn't exist yet.

  4. Developers could implement the PreferenceMetadata interface directly, and make it accessible to the Preferences library be registering it with a factory method.

There is nothing wrong with using a hybrid of all four approaches. Also, note that this is pay-as-you-go. If you do not want to make this information available to users of your components, you do not have to.

5. Provide an auditing mechanism to track where configuration information comes from. The first design point, above, defines an extension point to hook existing configuration mechanisms. This is great on the application development side, since all configuration information enters through the same API. However, it doesn't ease the learning curve for application deployers. Deployers still need to learn each and every legacy configuration scheme.

More specifically, deployers are looking for a solution to the following all-too-common problem:

  1. Application does not run correctly.

  2. Change configuration setting in file A.

  3. Application still does not run correctly, and seems to be ignoring configuration setting in file A.

  4. Bang head on wall for a while.

  5. Discover obscure bit of documentation to the effect that "Settings in File B override settings in File A if File B is on the classpath and has the 'override' attribute set."

One (flawed) approach to solving this problem would be to define and enforce a single model for for temporal and spatial scope. Then deployers could learn that one model and be done. The problem with this approach is that different components have different configuration needs. Some components can take all of their settings from one location. Others need to merge settings from several different locations. Similarly, different components will cache different settings for different lengths of time.

Rather than trying to create a shared model for all providers, it is more appropriate to simply require that providers tell the developer what they are doing. A configuration trace is the CCI equivalent of a stack trace to tell us where the configuration actually came from:

package java.util.prefs;
public abstract 
            class Preferences {
public void printConfigurationTrace(String 
            key);
//etc.
}

The printConfigurationTrace method simply provides a provider-specific trace of the "locations" consulted in deriving a particular piece of configuration data, and the times these locations were consulted. Here is a hypothetical example of printConfigurationTrace output.

javax.naming.factory.object
not found in 
            file jndi.properties (read Mon Jul 15 13:22:37 EDT 2002)
merged 
            from file c:/halloway/code/jndi.properties (read Mon Jul 15 16:06:15 
            EDT 2002)
merged from file c:/halloway/shared/jndi.properties 
            (read Mon Jul 15 16:06:15 EDT 2002)

Using this information, a deployer can quickly determine which locations are being consulted for configuration information. Of course, producing this output is more work for a component provider. This is inevitable. Only the component provider has this information. Failing to publish it is like refusing to publish the API used to call into a component.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020