I flew to Chicago in the spring of 1999 to consult on a project being done by ThoughtWorks, a small but rapidly growing application development company. One of the more ambitious enterprise application projects was a back-end leasing system. It deals with everything that happens after you sign a lease, including sending out bills, handling someone upgrade one of the assets on the lease, chasing people who don’t pay their bills on time, and figuring out what happens when someone returns the assets early. That doesn’t sound bad until you realize that leasing agreements are very complex. The business logic is written by business people to capture business, where odd small variations can make all the difference in winning a deal. Each victory adds to the complexity of the system.

A system of objects that can make the problem more tractable is the kind of thing that gets me excited. Making complex logic tractable is the primary benefit of objects. Developing a good. There is a domain model. Difficult but satisfying for a business problem.

That isn’t the end of the problem. Our domain model had to be persisted to a database in order to use a database. We had to connect this model to a user interface, provide support to allow remote applications to use our software, and integrate our software with third-party packages. Nobody in the world had ever used a new technology called J2EE.

We had the benefit of experience, even though this technology was new. I’ve been doing this for a long time with C, Smalltalk, and CORBA. The ThoughtWorkers had a lot of experience with it. We had key architectural ideas in our heads, and we had to figure out how to apply them to J2EE. The design is not perfect but it has stood the test of time.

This book was written for that situation. I’ve seen many enterprise application projects over the years. Similar design ideas have proven effective in dealing with the inevitable complexity of enterprise applications. Design ideas can be captured in this book as patterns.

There are a number of important topics in the design of enterprise applications covered in the first part of the book. Problems in the architecture of enterprise applications are introduced in these chapters. They don’t give much detail on the solutions. Patterns organize the details of the solutions in the second part. I don’t expect you to read the cover to cover of these patterns. To get a broad picture of what the book covers, you need to read the narrative chapters in Part 1 from start to finish, and then you need to read the patterns chapters in Part 2. The book is a short narrative book and a longer reference book.

The book is about enterprise application design. The display, manipulation, and storage of large amounts of often complex data and the support or automation of business processes with that data are what enterprise applications are about. Modern business includes reservation systems, financial systems, supply chain systems, and many others. Different from embedded systems, control systems, telecoms, or desktop productivity software, enterprise applications have their own challenges and solutions. Unless you want to get a feel for what enterprise applications are like, there’s nothing in this book for you.

Building enterprise applications have many architectural issues. This book can’t be a comprehensive guide to them. I’m a big fan of iterative development. The idea of delivering software as soon as you have something useful to the user is at the heart of iterative development. There are many differences between writing a book and writing software, but I think the two share the same idea. This book is incomplete but useful in its advice on enterprise application architecture. I talk about a lot of the same topics.

I don’t talk about a lot of things. I wanted to write about organizing validation, incorporating messaging and asynchronous communication, security, error handling, clustering, application integration, architectural refactoring, structuring rich-client user interface, among other topics. Because of space and time constraints, you won’t find them in this book. I hope to see some patterns for this work in the future. Maybe I will do a second volume someday and get into these topics, or someone else will fill the gaps.

Messages-based communication is a big issue. asynchronous message-based communication approaches are being used more and more by people who are integrating multiple applications. There’s a lot to be said for using them within an application. The book isn’t intended to be specific for any software platform. In the late ’80s and early ’90s, I came across these patterns while working with Smalltalk, C, and CORBA. I began to do extensive work in Java in the late ’90s and found that the patterns applied well to both early Java/CORBA systems and later J2EE-based work. I’ve been doing some initial work with Microsoft’s.NET platform and found the patterns apply again. My ThoughtWorks colleagues have introduced their experiences as well. I can’t claim generality across all platforms that have ever been used for enterprise applications, but the patterns have shown enough recurrence to be useful.

Code examples have been provided for most of the patterns. Most readers are likely to be able to read and understand what I choose to say for them. Java is a good choice. Java is less complex than C for anyone who can read it. C programmers can read Java but not vice versa. I like to use an oo language because I’m an object bigot. Most of the code examples are in Java. As I was working on the book, Microsoft started stabilizing its.NET environment, and its C# language has most of the same properties as Java for an author. Since developers don’t have much experience with.NET and so the idioms for using it are less mature, I did some code examples in C# as well. If you can read one of the languages, you should be able to read the other. Even if it’s not their preferred language, I wanted to use a language that the largest amount of software developers can read. I apologize to anyone who uses Smalltalk, Delphi,Visual Basic, Perl, Python, Ruby, or any other language. You think you know a better language than Java or C#. All I can say is that I do.

There are examples for inspiration and explanation of the patterns. You’ll need to do a bit of work to fit them into your application, but they aren’t canned solutions. Patterns are not destinations.

Who This Book Is For

I wrote this book for programmers, designers, and architects who are building enterprise applications and who want to improve their understanding of architectural issues or their communication about them.

Most of my readers will fall into two groups: those with modest needs who are looking to build their own software and readers with more demanding needs who will be using a tool. These patterns should get you started for those of modest needs. I’ll give you more of a headstart in this field than I did, but you’ll need more than the patterns will give. I hope this book will give you an idea of what’s happening under the hood and help you choose which of the tool-supported patterns to use. You have to make decisions about how to map certain situations using an object-relational mapping tool. The patterns should give you some idea of what to do.

There are people who want to build their own software. Carefully using tools is the first thing I’d say here. More than one project has been sucked into a long exercise at building frameworks, which isn’t what the project was really about. Go ahead if you’re still convinced. Many of the code examples in this book are simplified to help understand, and you’ll need to do a lot of tweaking to handle the greater demands you face.

Since patterns are common solutions to recurring problems, there is a good chance that you have already come across some of them. You may know most of them if you’ve been working in enterprise applications for a while. I’m not saying anything new in this book. I claim that this is a book of old ideas for our industry. I hope the book will help you learn about these techniques. I hope the book will help you communicate and teach the techniques to others. An important part of patterns is trying to build a common vocabulary. There is a remote Facade. Designers will know what you mean.

Martin Fowler, Melrose, Massachusetts, August 2002

0321127420P10162002

The emergence of new enabling technologies has helped the practice of enterprise application development. Java and.NET are examples of multi-tiered object-oriented platforms. Powerful applications can be built with the new tools and technologies, but they are not easy to implement. The developers of enterprise applications don’t understand the architectural lessons that experienced object developers have learned.

There are patterns of application architecture. It’s not like it’s like it’s like it’s like it’s like it’s like it’s like it’s like it’s like it’s like it’s like it’s like it’s like it’s like it It is written in response to stiff challenges faced by enterprise application developers. The same basic design ideas can be used to solve common problems despite the fact that technology has changed. With the help of an expert group of contributors, Martin distills over forty recurring solutions into patterns. The handbook of solutions is applicable to any enterprise application platform.

The book is two books in one. You can read from the beginning to the end of the first section on developing enterprise applications. The bulk of the book is a detailed reference to the patterns. Detailed code examples in Java or C# can be found in each pattern. The book is illustrated with diagrams to further explain the concepts.

With this book, you will have the knowledge necessary to make important architectural decisions about building an enterprise application and the proven patterns for use when building them.

The topics are covered in detail.

0321127420B10152002 –This text refers to an alternate kindle_edition edition.

I flew to Chicago in the spring of 1999 to consult on a project being done by ThoughtWorks, a small but rapidly growing application development company. One of the more ambitious enterprise application projects was a back-end leasing system. It deals with everything that happens after you sign a lease, including sending out bills, handling someone upgrade one of the assets on the lease, chasing people who don’t pay their bills on time, and figuring out what happens when someone returns the assets early. That doesn’t sound bad until you realize that leasing agreements are very complex. The business logic is written by business people to capture business, where odd small variations can make all the difference in winning a deal. Each victory adds to the complexity of the system.

A system of objects that can make the problem more tractable is the kind of thing that gets me excited. Making complex logic tractable is the primary benefit of objects. Developing a good. There is a domain model. Difficult but satisfying for a business problem.

That isn’t the end of the problem. Our domain model had to be persisted to a database in order to use a database. We had to connect this model to a user interface, provide support to allow remote applications to use our software, and integrate our software with third-party packages. Nobody in the world had ever used a new technology called J2EE.

We had the benefit of experience, even though this technology was new. I’ve been doing this for a long time with C, Smalltalk, and CORBA. The ThoughtWorkers had a lot of experience with it. We had key architectural ideas in our heads, and we had to figure out how to apply them to J2EE. The design is not perfect but it has stood the test of time.

This book was written for that situation. I’ve seen many enterprise application projects over the years. Similar design ideas have proven effective in dealing with the inevitable complexity of enterprise applications. Design ideas can be captured in this book as patterns.

There are a number of important topics in the design of enterprise applications covered in the first part of the book. Problems in the architecture of enterprise applications are introduced in these chapters. They don’t give much detail on the solutions. Patterns organize the details of the solutions in the second part. I don’t expect you to read the cover to cover of these patterns. To get a broad picture of what the book covers, you need to read the narrative chapters in Part 1 from start to finish, and then you need to read the patterns chapters in Part 2. The book is a short narrative book and a longer reference book.

The book is about enterprise application design. The display, manipulation, and storage of large amounts of often complex data and the support or automation of business processes with that data are what enterprise applications are about. Modern business includes reservation systems, financial systems, supply chain systems, and many others. Different from embedded systems, control systems, telecoms, or desktop productivity software, enterprise applications have their own challenges and solutions. Unless you want to get a feel for what enterprise applications are like, there’s nothing in this book for you.

Building enterprise applications have many architectural issues. This book can’t be a comprehensive guide to them. I’m a big fan of iterative development. The idea of delivering software as soon as you have something useful to the user is at the heart of iterative development. There are many differences between writing a book and writing software, but I think the two share the same idea. This book is incomplete but useful in its advice on enterprise application architecture. I talk about a lot of the same topics.

I don’t talk about a lot of things. I wanted to write about organizing validation, incorporating messaging and asynchronous communication, security, error handling, clustering, application integration, architectural refactoring, structuring rich-client user interface, among other topics. Because of space and time constraints, you won’t find them in this book. I hope to see some patterns for this work in the future. Maybe I will do a second volume someday and get into these topics, or someone else will fill the gaps.

Messages-based communication is a big issue. asynchronous message-based communication approaches are being used more and more by people who are integrating multiple applications. There’s a lot to be said for using them within an application. The book isn’t intended to be specific for any software platform. In the late ’80s and early ’90s, I came across these patterns while working with Smalltalk, C, and CORBA. I began to do extensive work in Java in the late ’90s and found that the patterns applied well to both early Java/CORBA systems and later J2EE-based work. I’ve been doing some initial work with Microsoft’s.NET platform and found the patterns apply again. My ThoughtWorks colleagues have introduced their experiences as well. I can’t claim generality across all platforms that have ever been used for enterprise applications, but the patterns have shown enough recurrence to be useful.

Code examples have been provided for most of the patterns. Most readers are likely to be able to read and understand what I choose to say for them. Java is a good choice. Java is less complex than C for anyone who can read it. C programmers can read Java but not vice versa. I like to use an oo language because I’m an object bigot. Most of the code examples are in Java. As I was working on the book, Microsoft started stabilizing its.NET environment, and its C# language has most of the same properties as Java for an author. Since developers don’t have much experience with.NET and so the idioms for using it are less mature, I did some code examples in C# as well. If you can read one of the languages, you should be able to read the other. Even if it’s not their preferred language, I wanted to use a language that the largest amount of software developers can read. I apologize to anyone who uses Smalltalk, Delphi,Visual Basic, Perl, Python, Ruby, or any other language. You think you know a better language than Java or C#. All I can say is that I do.

There are examples for inspiration and explanation of the patterns. You’ll need to do a bit of work to fit them into your application, but they aren’t canned solutions. Patterns are not destinations.

Who This Book Is For

I wrote this book for programmers, designers, and architects who are building enterprise applications and who want to improve their understanding of architectural issues or their communication about them.

Most of my readers will fall into two groups: those with modest needs who are looking to build their own software and readers with more demanding needs who will be using a tool. These patterns should get you started for those of modest needs. I’ll give you more of a headstart in this field than I did, but you’ll need more than the patterns will give. I hope this book will give you an idea of what’s happening under the hood and help you choose which of the tool-supported patterns to use. You have to make decisions about how to map certain situations using an object-relational mapping tool. The patterns should give you some idea of what to do.

There are people who want to build their own software. Carefully using tools is the first thing I’d say here. More than one project has been sucked into a long exercise at building frameworks, which isn’t what the project was really about. Go ahead if you’re still convinced. Many of the code examples in this book are simplified to help understand, and you’ll need to do a lot of tweaking to handle the greater demands you face.

Since patterns are common solutions to recurring problems, there is a good chance that you have already come across some of them. You may know most of them if you’ve been working in enterprise applications for a while. I’m not saying anything new in this book. I claim that this is a book of old ideas for our industry. I hope the book will help you learn about these techniques. I hope the book will help you communicate and teach the techniques to others. An important part of patterns is trying to build a common vocabulary. There is a remote Facade. Designers will know what you mean.

Martin Fowler, Melrose, Massachusetts, August 2002

0321127420P10162002 –This text refers to an alternate kindle_edition edition.