Apache Camel Developer's Cookbook

Apache Camel Developer's Cookbook

Overview of this book

Apache Camel is a de-facto standard for developing integrations in Java, and is based on well-understood Enterprise Integration Patterns. It is used within many commercial and open source integration products. Camel makes common integration tasks easy while still providing the developer with the means to customize the framework when the situation demands it. Tasks such as protocol mediation, message routing and transformation, and auditing are common usages of Camel. Apache Camel Developer's Cookbook provides hundreds of best practice tips for using Apache Camel in a format that helps you build your Camel projects. Each tip or recipe provides you with the most important steps to perform along with a summary of how it works, with references to further reading if you need more information. This book is intended to be a reliable information source that is quicker to use than an Internet search. Apache Camel Developer's Cookbook is a quick lookup guide that can also be read from cover to cover if you want to get a sense of the full power of Apache Camel. This book provides coverage of the full lifecycle of creating Apache Camel-based integration projects, including the structure of your Camel code and using the most common Enterprise Integration patterns. Patterns like Split/Join and Aggregation are covered in depth in this book. Throughout this book, you will be learning steps to transform your data. You will also learn how to perform unit and integration testing of your code using Camel's extensive testing framework, and also strategies for debugging and monitoring your code. Advanced topics like Error Handling, Parallel Processing, Transactions, and Security will also be covered in this book. This book provides you with practical tips on using Apache Camel based on years of hands-on experience from hundreds of integration projects.

Apache Camel Developer's Cookbook

Credits

About the Authors

Acknowledgments

About the Reviewers

www.PacktPub.com

Preface

Free Chapter

Structuring Routes

Introduction

Using Camel in a Java application

Embedding Camel in a Spring application

Using Camel components

Reusing routing logic by connecting routes

Asynchronously connecting routes

Spanning Camel contexts within a single Java process

Using external properties in Camel routes

Reusing endpoints

Reusing routing logic through template routes

Controlling route startup and shutdown

Message Routing

Introduction

Content Based Routing

Filtering out unwanted messages

Wire Tap – sending a copy of the message elsewhere

Multicast – routing the same message to many endpoints

Recipient List – routing a message to a list of endpoints

Throttler – restricting the number of messages flowing to an endpoint

Request-response route sending a one-way message

One-way route waiting on a request-response endpoint

Dynamic Routing – making routing decisions at runtime

Load balancing across a number of endpoints

Routing Slip – routing a message to a fixed list of endpoints

Routing to Your Code

Introduction

Routing messages directly to a Java method

Sending messages directly to a Camel endpoint

Using a Java method as a Predicate

Writing a custom Camel Processor

Mapping the message to method parameters

Writing a custom data marshaller

Writing a custom data type converter

Transformation

Introduction

Transforming using a Simple Expression

Transforming inline with XQuery

Transforming with XSLT

Transforming from Java to XML with JAXB

Transforming from Java to JSON

Transforming from XML to JSON

Parsing comma-separated values (CSV)

Enriching your content with some help from other endpoints

Normalizing messages into a common XML format

Splitting and Aggregating

Introduction

Splitting a message into fragments

Splitting XML messages

Processing split messages in parallel

Aggregating related messages

Aggregating with timeouts

Aggregating with intervals

Processing aggregated messages in parallel

Splitting a message, and processing and gathering responses

Splitting messages and re-aggregating them using different criteria

Parallel Processing

Introduction

Increasing message consumption through multiple endpoint consumers

Spreading the load within a route using a set of threads

Routing a request asynchronously

Using custom thread pools

Using thread pool profiles

Working with asynchronous APIs

Error Handling and Compensation

Introduction

Logging errors

Dead Letter Channel – handling errors later

Retrying an operation

Conditional retry

Customizing each redelivery attempt

Catching exceptions

Marking exceptions as handled

Fine-grained error handling using doTry…doCatch

Defining completion actions

Defining completion actions dynamically

Transactions and Idempotency

Introduction

Preventing duplicate invocation of routing logic

Transactional file consumption

Using transactions with a database

Limiting the scope of a transaction

Rolling back a transaction

Using transactions with messaging

Idempotency inside transactions

Setting up XA transactions over multiple transactional resources

Testing

Introduction

Testing routes defined in Java

Using mock endpoints to verify routing logic

Replying from mock endpoints

Testing routes defined in Spring

Testing routes defined in OSGi Blueprint

Auto-mocking of endpoints

Validating route behavior under heavy load

Unit testing processors and Bean Bindings

Testing routes with fixed endpoints using AOP

Testing routes with fixed endpoints using conditional events

Monitoring and Debugging

Introduction

Logging meaningful steps within your route

Debugging using logging

Throughput logging

Enabling step-by-step tracing in code

Disabling JMX

Configuring JMX

Naming your routes to make it easier to monitor

Adding JMX attributes and operations

Monitoring other systems using the Camel JMX Component

Setting breakpoints in your routes

Security

Introduction

Encrypting configuration properties

Digitally signing and verifying messages

Encrypting and decrypting a message

Encrypting all or parts of an XML message

Authentication and authorization using Spring Security

Web Services

Introduction

Generating the service stubs from a WSDL

Invoking a remote web service from Camel

Implementing a web service with a Camel route

Providing multiple web service operations within a single route

Handling web service faults

Web service proxying

Index

Customer Reviews

5 star

4 star

3 star

2 star

1 star

Defining completion actions

When developing integrations, you will at some point work with non-transactional resources that maintain some sort of state, such as web service endpoints. As an exchange is processed through your routes, it will trigger calls to these endpoints, modifying that state.

We have already seen how a compensating operation may be triggered when an exception is thrown in the Fine-grained error handling using doTry…doCatch recipe. As an example, if the original operation called was place order, you may have to call a cancel order operation to unwind it.

Camel's DSL contains an onCompletion statement, which allows you to define actions taken when a message completes successfully or fails at the level of a route.

This allows multiple levels of failure compensation to be written cleanly without nesting doTry..doCatch..doFinally blocks.

This mechanism can also be used to implement a two stage pessimistic transaction process, such as:

Call an initial operation that you intend to...

Apache Camel Developer's Cookbook

Apache Camel Developer's Cookbook

Overview of this book

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Apache Camel Developer's Cookbook

Defining completion actions