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Tips covering design patterns that are relevant to Java performance. This is the place to start if you are near the beginning of a project.

The following pages have their detailed tips extracted below

• Balancing Network Load with Priority Queues
• Designing Entity Beans for Improved Performance
• Performance tuning report in German
• Design patterns catalog
• Design Patterns
• J2EE Design Patterns for the presentation tier
• Performance tuning
• Alternatives to using 'new'.
• J2EE design patterns to improve performance
• Performance optimizing design patterns for J2EE
• Article on recycling resource pools
• EJB performance tips
• Pattern performance tips
• The Verified Service Locator pattern
• Sun Community chat on Java BluePrints
• Object Resource Pooling
• Using NIO
• J2EE best practices.
• Rules and Patterns for Session Facades
• Local entity beans
• J2EE challenges
• The Optimistic Locking pattern
• Object creation tuning
• J2EE design optimizations
• The Proxy design pattern.
• Customized high-speed, fine-grained access control

The following detailed tips have been extracted from the raw tips page

http://www.ddjembedded.com/resources/articles/2001/0112g/0112g.htm
Balancing Network Load with Priority Queues (Page last updated December 2001, Added 2002-02-22, Author Frank Fabian, Publisher Dr. Dobb's). Tips:

• Sort incoming requests into different priority queues, and service the requests according to the priorities assigned to each queue. [Article gives the example where combining user and automatic requests in one queue can result in a worst case user wait of 3.5 minutes, as opposed to less than 0.1 seconds if priority queues are used].

http://developer.java.sun.com/developer/technicalArticles/ebeans/ejbperformance/
Designing Entity Beans for Improved Performance (Page last updated March 2001, Added 2001-03-21, Author Beth Stearns, Publisher Sun). Tips:

• Use a value object which encapsulates all of an entity's data attributes, and which transfers all the data in one network transfer. This may result in large objects being transferred though.

http://www.bastie.de/resource/res/mjp.pdf and http://www.bastie.de/java/mjperformance/contents.html
Performance tuning report in German. Thanks to Peter Kofler for extracting the tips. (Page last updated November 2001, Added 2001-07-20, Author Sebastian Ritter, Publisher Ritter). Tips:

• use the flyweight pattern to reduce object creation [The flyweight pattern uses a factory instead of 'new' to reuse objects rather than always create new ones].

http://java.sun.com/blueprints/patterns/j2ee_patterns/catalog.html
Design patterns catalog (Page last updated 2001, Added 2002-01-25, Author ?, Publisher Sun). Tips:

• [Page lists some patterns with summaries and links to detailed info. Patterns are: Data Access Object; Fast-Lane Reader; Front Controller; Page-by-Page Iterator; Session Facade; Value Object].
• Use the Data Access Object pattern to decouple business logic from data access logic, allowing for optimizations to be made in how data is managed.
• Use the Fast-Lane Reader pattern to accelerate read-only data access by not using enterprise beans.
• Use the Front Controller pattern to centralize incoming client requests, allowing optimizations to be made in aggregating the resulting view.
• Use the Page-by-Page Iterator pattern to efficiently access a large, remote list by retrieving its elements one sublist of value objects at a time.
• Use the Session Facade pattern to provide a unified, workflow-oriented interface to a set of enterprise beans, thus minimizing client calls to server EJBs.
• Use the Value Object pattern to efficiently transfer remote, fine-grained data by sending a coarse-grained view of the data.

http://developer.java.sun.com/developer/technicalArticles/J2EE/despat/
Design Patterns (Page last updated January 2002, Added 2002-01-25, Author Vijay Ramachandran, Publisher Sun). Tips:

• [Article discusses several design patterns: Model-View-Controller, Front Controller, Session Facade, Data Access Object].
• Use the Front Controller pattern to channel all client requests through a single decision point, which allows the application to be balanced at runtime.
• Use a Session Facade to provide a simple interface to a complex subsystem of enterprise beans, and to reduce network communication requirements.
• Use Data Access Objects to decouple the business logic from the data access logic, allowing data access optimizations to be decoupled from other types of optimizations.

http://www.onjava.com/pub/a/onjava/2002/01/16/patterns.html
J2EE Design Patterns for the presentation tier (Page last updated January 2002, Added 2002-01-25, Author Sue Spielman, Publisher OnJava). Tips:

• [Article discusses several design patterns: Intercepting Filter, Front Controller, View Helper, Composite View, Service To Worker, Dispatch View. Performance is not explicitly covered, but at least a couple are relevant to getting good performance].

http://www.sys-con.com/java/article.cfm?id=1149
Performance tuning (Page last updated September 2001, Added 2001-10-22, Author James McGovern, Publisher Java Developers Journal). Tips:

• Use the factory pattern to enable reuse or cloning of objects.

http://www.ddj.com/documents/ddj0204a/
Alternatives to using 'new'. (Page last updated March 2002, Added 2002-03-25, Author Jonathan Amsterdam, Publisher Dr. Dobb's). Tips:

• The Singleton pattern and the Flyweight (object factory) pattern are useful to limit numbers of objects of various types and to assist with object reuse and reduce garbage collection.
• Using variables to provide access to limited numbers of objects is efficient, but a maintenance problem if you need to change the object access pattern, for example from a global singleton to a ThreadLocal Singleton.
• A non-static factory method is polymorphic and so provides many advantages over static factory methods.
• The Abstract Factory design pattern uses a single class to create more than one kind of object.
• An alternative to the Flyweight pattern is the Prototype pattern, which allows polymorphic copies of existing objects. The Object.clone() method signature provides support for the Prototype pattern.
• Prototypes are useful when object initialization is expensive, and you anticipate few variations on the initialization parameters. Then you could keep already-initialized objects in a table, and clone an existing object instead of expensively creating a new one from scratch.
• Immutable objects can be returned directly when using Prototyping, avoiding the copying overhead.

http://www.javaworld.com/javaworld/javaone01/j1-01-patterns.html
J2EE design patterns to improve performance (Page last updated June 2001, Added 2001-06-18, Author Daniel H. Steinberg, Publisher JavaWorld). Tips:

• Combine multiple remote calls for state information into one call using a value object to wrap the data (the Value Object pattern, superceded by local interfaces in EJB 2.0).
• Where long lists of data are returned by queries, use the Page-by-Page Iterator pattern: a server-side object that holds data on the server and supplies batches of results to the client.

http://developer.java.sun.com/developer/technicalArticles/J2EE/J2EEpatterns/
Performance optimizing design patterns for J2EE (Page last updated December 2001, Added 2001-12-26, Author Vijay Ramachandran, Publisher Sun). Tips:

• For read-only access to a set of data that does not change rapidly, use the Fast Lane Reader pattern which bypasses the EJBs and uses a (possibly non-transactional) data access object which encapsulates access to the data. Use the Fast Lane Reader to read data from the server and display all of them in one shot.
• When you need to access a large remote list of objects, use the Page-by-Page Iterator pattern which sends smaller subsets of the data as requested until the client no longer want any more data. Use the Page-by-Page Iterator to send lists of simple objects from EJBs to clients.
• When the client would request many small data items which would require many remote calls to satisfy, combine the multiple calls into one call which results in a single Value Object which holds all the data required to be transferred. Use the Value Object to send a single coarse-grained object from the server to the client(s).

http://www.javaworld.com/javaworld/javatips/jw-javatip78.html
Article on recycling resource pools (Page last updated 1998, Added 2000-12-20, Authors Philip Bishop and Nigel Warren, Publisher JavaWorld). Tips:

• Use the builder pattern: break the construction of complex objects into a series simpler Builder objects, and a Director object which combines the Builders to form the complex object. Then you can use Recycler (a type of Director) to replace only the broken parts of the complex object, so reducing the amount of objects that need to be recreated.

http://www.precisejava.com/javaperf/j2ee/EJB.htm
EJB performance tips (Page last updated November 2001, Added 2001-12-26, Authors Ravi Kalidindi and Rohini Datla, Publisher PreciseJava). Tips:

• Wrap multiple entity beans in a session bean to change multiple EJB remote calls into one session bean remote call and several local calls (pattern called SessionFacade).
• Change multiple remote method calls into one remote method call with all the data combined into a parameter object.
• Cache EJBHome references to avoid JNDI lookup overhead (pattern called ServiceLocator).

http://www.precisejava.com/javaperf/j2ee/Patterns.htm
Pattern performance tips (Page last updated November 2001, Added 2001-12-26, Authors Ravi Kalidindi and Rohini Datla, Publisher PreciseJava). Tips:

• The ServiceLocator/EJBHomeFactory Pattern reduces the expensive JNDI lookup process by caching EJBHome objects.
• The SessionFacade Pattern reduces network calls by combining accesses to multiple Entity beans into one access to the facade object.
• The MessageFacade/ServiceActivator Pattern moves method calls into a separate object which can execute asynchronously.
• The ValueObject Pattern combines remote data into one serializable object, thus reducing the number of network transfers required to access multiple items of remote data.
• The ValueObjectFactory/ValueObjectAssembler Pattern combines remote data from multiple remote objects into one serializable object, thus reducing the number of network transfers required to access multiple items of remote data.
• The ValueListHandler Pattern: avoids using multiple Entity beans to access the database, using Data Access Objects which explicitly query the database; and returns the data to the client in batches (which can be terminated) rather than in one big chunk, according to the Page-by-Page Iterator pattern.
• The CompositeEntity Pattern reduces the number of actual entity beans by wrapping multiple java objects (which could otherwise be Entity beans) into one Entity bean.

http://www.javaworld.com/javaworld/jw-07-2002/jw-0703-service.html
The Verified Service Locator pattern (Page last updated July 2002, Added 2002-07-24, Author Paulo Caroli, Publication JavaWorld, Publisher JavaWorld). Tips:

• The Service Locator pattern improves performance by caching service objects that have a high-lookup cost.
• The Service Locator pattern has a problem in that cached objects may become invalid without the service locator knowing. The Verified Service Locator pattern periodically tests the validity of the caches objects to avoid providing invalid service objects to requestors.

http://developer.java.sun.com/developer/community/chat/JavaLive/2002/jl0515.html
Sun Community chat on Java BluePrints (Page last updated May 2002, Added 2002-07-24, Author Edward Ort, Publication Sun Developer, Publisher Sun). Tips:

• Make tightly coupled components local to each other. Put remote beans primarily as facades across subsystems.
• The page-by-page pattern is designed to handle cases where the result set is large, and the end-user is not interested in seeing all of the results. There is really no upper threshold for the size of result set in the pattern.

http://www.ociweb.com/jnb/jnbMar2002.html
Object Resource Pooling (Page last updated March 2002, Added 2002-03-25, Author Paul King, Publisher OCI). Tips:

• The Recycler pattern fixes only the broken parts of a failed object, to minimize the replacement cost.

http://www-106.ibm.com/developerworks/java/library/j-javaio/
Using NIO (Page last updated March 2002, Added 2002-03-25, Author Aruna Kalagnanam and Balu G., Publisher IBM). Tips:

• The Reactor design pattern demultiplexes events and dispatches them to registered object handlers. (The Observer pattern is similar, but handles only a single source of events where the Reactor pattern handles multiple event sources).

http://www.hpmiddleware.com/newsletters/webservicesnews/features/
J2EE best practices. (Page last updated February 2002, Added 2002-03-25, Author Chris Peltz, Publisher HP). Tips:

• Executing a search against the database calls one of the finder() methods. finder() methods must return a collection of remote interfaces, not ValueObjects. Consequently the client would need to make a separate remote call for each remote interface received, to acquire data. The SessionFacade pattern suggests using a session bean to encapsulate the query and return a collection of ValueObjects, thus making the request a single transfer each way.
• The Value Object Assembler pattern uses a Session EJB to aggregate all required data as various types of ValueObjects. This pattern is used to satisfy one or more queries a client might need to execute in order to display multiple data types.

http://www7b.boulder.ibm.com/wsdd/library/techarticles/0106_brown/sessionfacades.html
Rules and Patterns for Session Facades (Page last updated June 2001, Added 2001-07-20, Author Kyle Brown, Publisher IBM). Tips:

• Use the Facade pattern, and specifically Value objects, to transfer all the subset of data needed from an entity bean in one transfer.

http://www.sys-con.com/java/article.cfm?id=1160
Local entity beans (Page last updated October 2001, Added 2001-10-22, Author Alex Pestrikov, Publisher Java Developers Journal). Tips:

• Facade objects (wrappers) allow local entity beans to be called remotely. This pattern incurs very little overhead for remote calls, while at the same time optimizing local calls between local beans which can use local calls.

http://www.sys-con.com/java/article.cfm?id=712
J2EE challenges (Page last updated June 2001, Added 2001-07-20, Author Chris Kampmeier, Publisher Java Developers Journal). Tips:

• To ensure good performance use experienced J2EE builders and use proven design patterns.

http://www.javaworld.com/javaworld/jw-07-2001/jw-0713-optimism.html
The Optimistic Locking pattern (Page last updated July 2001, Added 2001-07-20, Author Yasmin Akbar-Husain and Eoin Lane, Publisher JavaWorld). Tips:

• Optimistic locking only checks data integrity at update time, so has no lock contention [but can have high rollback costs]. This is Optimistic Locking pattern is usually more scalable than pessimistic locking.
• Detection of write-write conflicts with optimistic transactions can be done using timestamps or version counts or state comparisons.

http://www.numega.com/library/dmpapers/javamem.shtml
Object creation tuning (Page last updated 2000, Added 2001-07-20, Author Daniel F. Savarese, Publisher Numega). Tips:

• Use a factory class instead of directly calling the "new" operator, to allow easier reuse of objects.

http://www.sys-con.com/java/article.cfm?id=1135
J2EE design optimizations (Page last updated September 2001, Added 2001-10-22, Author Vijay S. Ramachandran, Publisher Java Developers Journal). Tips:

• For data that changes infrequently (i.e. rarely enough that a user session will not need that data updating during the session lifetime), avoid transactional access by using a cached Data Access Object rather than the transactional EJB (this is called the Fast Lane Reader pattern).
• Don't transfer long lists of data to the user, transfer a page at a time (this is called the Page-by-Page Iterator pattern).
• Instead of making lots of remote requests for data attributes of an object, combine the attributes into another object and send the object to the client. Then the attributes can be queried efficiently locally (this is called the Value Object pattern). Consider caching the value objects where appropriate.

http://www.javaworld.com/javaworld/jw-02-2002/jw-0222-designpatterns.html
The Proxy design pattern. (Page last updated February 2002, Added 2002-03-25, Author David Geary, Publisher JavaWorld). Tips:

• Using a proxy, you can delay image loading until the image is required.
• The Proxy pattern often instantiates its real object, the Decorator pattern (which can also use proxy objects) rarely does.
• The java.lang.reflect package provides three classes to support the Proxy and Decorator patterns: Proxy, Method, and InvocationHandler.

http://www.javaworld.com/jw-09-2001/jw-0914-access.html
Customized high-speed, fine-grained access control (Page last updated September 2001, Added 2001-10-22, Author Wally Flint, Publisher JavaWorld). Tips:

• [Article discusses an Access control pattern which has no performance penalty].