Groovy 2 Cookbook

Groovy 2 Cookbook

Overview of this book

Get up to speed with Groovy, a language for the Java Virtual Machine (JVM) that integrates features of both object-oriented and functional programming. This book will show you the powerful features of Groovy 2 applied to real-world scenarios and how the dynamic nature of the language makes it very simple to tackle problems that would otherwise require hours or days of research and implementation. Groovy 2 Cookbook contains a vast number of recipes covering many facets of today's programming landscape. From language-specific topics such as closures and metaprogramming, to more advanced applications of Groovy flexibility such as DSL and testing techniques, this book gives you quick solutions to everyday problems. The recipes in this book start from the basics of installing Groovy and running your first scripts and continue with progressively more advanced examples that will help you to take advantage of the language's amazing features. Packed with hundreds of tried-and-true Groovy recipes, Groovy 2 Cookbook includes code segments covering many specialized APIs to work with files and collections, manipulate XML, work with REST services and JSON, create asynchronous tasks, and more. But Groovy does more than just ease traditional Java development: it brings modern programming features to the Java platform like closures, duck-typing, and metaprogramming. In this new book, you'll find code examples that you can use in your projects right away along with a discussion about how and why the solution works. Focusing on what's useful and tricky, Groovy 2 Cookbook offers a wealth of useful code for all Java and Groovy programmers, not just advanced practitioners.

Groovy 2 Cookbook

Credits

About the Authors

About the Reviewers

www.PacktPub.com

Preface

Free Chapter

Getting Started with Groovy

Introduction

Installing Groovy on Windows

Installing Groovy on Linux and OS X

Executing Groovy code from the command line

Using Groovy as a command-line text file editor

Using Groovy to start a server on the command line

Running Groovy with invokedynamic support

Building Groovy from source

Managing multiple Groovy installations on Linux

Using groovysh to try out Groovy commands

Starting groovyConsole to execute Groovy snippets

Configuring Groovy in Eclipse

Configuring Groovy in IntelliJ IDEA

Using Groovy Ecosystem

Introduction

Using Java classes from Groovy

Embedding Groovy into Java

Compiling Groovy code

Simplifying dependency management with Grape

Integrating Groovy into the build process using Ant

Integrating Groovy into the build process using Maven

Integrating Groovy into the build process using Gradle

Generating documentation for Groovy code

Checking Groovy code's quality with CodeNarc

Using Groovy Language Features

Introduction

Searching strings with regular expressions

Writing less verbose Java Beans with Groovy Beans

Inheriting constructors in Groovy classes

Adding the cloning functionality to Groovy Beans

Defining code as data in Groovy

Defining data structures as code in Groovy

Implementing multiple inheritance in Groovy

Adding a functionality to the existing Java/Groovy classes

Defining type-checking rules for dynamic code

Adding automatic logging to Groovy classes

Working with Files in Groovy

Introduction

Reading from a file

Reading a text file line by line

Processing every word in a text file

Writing to a file

Replacing tabs with spaces in a text file

Filtering a text file's content

Deleting a file or directory

Walking through a directory recursively

Searching for files

Changing file attributes on Windows

Reading data from a ZIP file

Reading an Excel file

Extracting data from a PDF

Working with XML in Groovy

Introduction

Reading XML using XmlSlurper

Reading XML using XmlParser

Reading XML content with namespaces

Searching in XML with GPath

Searching in XML with XPath

Constructing XML content

Modifying XML content

Sorting XML nodes

Serializing Groovy Beans to XML

Working with JSON in Groovy

Introduction

Parsing JSON messages with JsonSlurper

Constructing JSON messages with JsonBuilder

Modifying JSON messages

Validating JSON messages

Converting JSON message to XML

Converting JSON message to Groovy Bean

Using JSON to configure your scripts

Working with Databases in Groovy

Introduction

Creating a database table

Connecting to an SQL database

Querying an SQL database

Modifying data in an SQL database

Calling a stored procedure

Reading BLOB/CLOB from a database

Building a simple ORM framework

Using Groovy to access Redis

Using Groovy to access MongoDB

Using Groovy to access Apache Cassandra

Working with Web Services in Groovy

Introduction

Downloading content from the Internet

Executing an HTTP GET request

Executing an HTTP POST request

Constructing and modifying complex URLs

Issuing a REST request and parsing a response

Issuing a SOAP request and parsing a response

Consuming RSS and Atom feeds

Using basic authentication for web service security

Using OAuth for web service security

Metaprogramming and DSLs in Groovy

Introduction

Querying methods and properties

Dynamically extending classes with new methods

Overriding methods dynamically

Adding performance logging to methods

Adding a caching functionality around methods

Adding transparent imports to a script

DSL for executing commands over SSH

DSL for generating reports from logfiles

Concurrent Programming in Groovy

Introduction

Processing collections concurrently

Downloading files concurrently

Splitting a large task into smaller parallel jobs

Running tasks in parallel and asynchronously

Using actors to build message-based concurrency

Using STM to atomically update fields

Using dataflow variables for lazy evaluation

Index

Customer Reviews

5 star

4 star

3 star

2 star

1 star

Using Groovy as a command-line text file editor

The groovy command, which we introduced in the Executing Groovy code from the command line recipe, can also be used as a stream editor or text file filter. In this recipe, we will cover the -i, -n, and -p parameters that can be used to leverage file editing and processing functionality.

How to do it...

Assume that you have a file, data.txt, which contains five lines with numbers from 1 to 5:

To multiply each number by 2, you can use the following command:
```
groovy -n -e "println line.toLong() * 2" data.txt
```
We can even omit the println method call if we pass additional the -p parameter to the command:
```
groovy -n -p -e "line.toLong() * 2" data.txt
```
In both cases, Groovy will print the following output:
```
2
4
6
8
10
```

How it works...

Due to the fact that we are using the -n option, the code in double quotes is applied to each line read from the datafile specified as the last parameter in the command line. The line variable is predefined by Groovy, and you can use it to access, filter, or modify the line's content.

There's more...

If you add the -i option to the previous command, then it will actually modify the input file, with output values as follows:

groovy -i -n -p -e "line.toLong() * 2" data.txt

Adding a suffix .bak to the -i option will save the original input file data.txt under data.txt.bak:

groovy -i .bak -n -p -e "line.toLong() * 2" data.txt

You can use the -n and -p options to filter the input stream of other operating system commands. For example, if you want to filter the output of a directory listing command (dir) to show only the *.jar files, on Windows you can use the following command:

dir | groovy -n -e "if (line.contains('.jar')) println line"

Or on *nix-based operating systems, you can use the following command:

ls -la | groovy -n -e "if (line.contains('.jar')) println line"

Of course, the result of the previous commands can be easily achieved by more efficient operating system instructions. However, these examples are given to demonstrate that you can actually leverage the full power of the Groovy and Java programming languages to implement more complex processing rules.

Groovy 2 Cookbook

Groovy 2 Cookbook

Overview of this book

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Current Title:

Groovy 2 Cookbook

Using Groovy as a command-line text file editor

How to do it...

How it works...

There's more...

See also