Using Groovy Language Features
If the Sample class is annotated with @TypeChecked, the compiler will return:
[Static type checking] -
Cannot find matching method java.lang.Object#toUpperCase(). Please check if the declared type is right
and if the method exists. @ line 77, column 44.
wo','three'].collect { println it.toUpper
^
What is happening here? Simply, the compiler has no idea of the type of the implicit variable it, which is often used inside closures to make the code even more terse. This compilation error can be solved by explicitly declaring the closure variable as follows:
['one','two','three'].collect {
myString -> println myString.toUpperCase()
}
Adding automatic logging to Groovy classes
In the Writing less verbose Java Beans with Groovy Beans, Adding the cloning functionality to Groovy Beans, and Inheriting constructors in Groovy classes recipes, we met some of the
annotation-based AST transformations available in Groovy. An AST transformation is a process in which a programmer is able to hook into the bytecode generation process and influence the final shape of the resulting bytecode. Groovy ships with many useful transformations and in this recipe, we are going to look at the family of logging annotations.
How to do it...
The transformation we are going to demonstrate is the @groovy.util.logging.Log annotation that injects java.util.logging.Logger into a Groovy class:
1.Let's apply the annotation to a Groovy class:
@groovy.util.logging.Log class UserService {
def createUser(String username, String password) { log.info("creating user with name ${username}")
}
}
2.And call the method of the new class:
def userService = new UserService() userService.createUser('john', 'secret')
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3.The output will be:
INFO: creating user with name john
How it works...
The annotation takes a number of steps. First, it creates a logger with the variable name log and injects it in the class as a static final variable. Then it surrounds every call to the logger with a conditional check to verify whether the log level is enabled. No need to pollute your code with hard-to-read if statements just to check whether the log statement should
be evaluated.
The variable that holds the logger can be modified by using an attribute on the annotation:
@groovy.util.logging.Log('someLogger') class UserService { ... }
There's more...
The logging transformation is not limited to use only one logging framework but it also allows to use the following logging facilities by changing the annotation class:
ff @groovy.util.logging.Commons: It injects an Apache Commons logger and initializes it using LogFactory.getLog(class).
ff @groovy.util.logging.Log4j: It injects Log4J org.apache.log4j.Logger into the class and initializes it using Logger.getLogger(class).
ff @groovy.util.logging.Slf4j: It injects a Slf4J logger into the annotated class and initializes it using org.slf4j.LoggerFactory.getLogger(class). Slf4J is the underlying logger used by the newer framework Logback. If you wish to use that framework you should use the @Slf4j annotation.
See also
ff http://groovy.codehaus.org/api/groovy/util/logging/Log.html
ff http://docs.oracle.com/javase/7/docs/api/java/util/logging/ Logger.html
ff http://commons.apache.org/proper/commons-logging/ ff http://logging.apache.org/log4j
ff http://www.slf4j.org/
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4
Working with Files in Groovy
In this chapter, we will cover:
ff ff ff ff ff ff ff ff ff ff ff ff ff
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
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