/AwesomeJavaLibraryExamples

A collection of examples for various libraries in the Java world

Primary LanguageJavaThe UnlicenseUnlicense

The Java Library System

Have you ever been sitting there writing your own PDF generation code and find yourself hoping that sysadmin doesn’t upgrade the company from Acrobat Reader from version 5.0 to 10, because your PDF would no longer render? Well never fear the Java library ecosystem is here to save you from that worry and thousands of others just like it.

Difference between a library and a framework

The key difference between a library and a framework is "Inversion of Control". When you call a method from a library, you are in control. But with a framework, the control is inverted: the framework calls you.

The above quote sums up the idea of these examples quite well. I was originally going to include Spring and JUnit in these examples, but upon further reflection that while they are provided as library jars like everything else in the Java world they aren't strictly what I would consider a library. Logging is probably not exactly a library based on this definition, but since all the calls to do work are via calls pragmatically to log some message to an output it is less of a framework.

Getting started

The project uses Gradle for it's builds to simplify dependency (library) management as well as quick and easy JAR creation for running the examples. It does in my opinion abuse what you should use the Gradle multi-project support so please do not do this with a production system.

  1. Clone this project
    1. git clone https://github.com/developerSid/AwesomeJavaLibraryExamples.git
  2. Change directory to the one created by the clone
    1. cd AwesomeJavaLibraryExamples
  3. Build projects
    1. ./gradlew clean build
      • This builds an uberjar for all the projects to make it easy to run the examples. Normally this is something that would be handled by other Gradle plugins or you'd build a classpath containing all the libraries you need. So please do not use this in production, instead use the Spring-boot Gradle plugin

Apache Commons

Apache Commons is broken up into three parts

  1. Apache Commons Proper
    1. "A repository of reusable Java components"
    2. Projects here are kept up to date and have continuing development and support.
  2. Apache Commons Sandbox
    1. "A workspace for Java component development"
    2. Newer development happens here for projects that hope to one day make it into Proper
    3. May or may not be maintained anymore
  3. Apache Commons Dormant
    1. "A repository of components that are currently inactive"
    2. Basically dead no longer maintained code that you can still use, but you will be on your own supporting it. At least it is open source so if there is something you can use to bootstrap something you are working on you can always fork and maintain yourself

Root of Apache Commons Proper. There are many sub projects here that are currently maintained and are usually meant to solve a single problem that is reusable within your projects.

Apache Commons Lang

  • Apache Commons Lang - The Stuff nobody on the JCP thought should be in the standard library (because they don't actually have to write business logic in Java)
    • StringUtils - org.apache.commons.lang3.StringUtils
      • You should use this when
        • Avoid null checks in your code
        • Do simple String operations you do a lot of with less code
      • To run the examples (./gradlew clean build)
        1. java -cp Lang/build/libs/Lang.jar org.devict.jlib.lang.ExampleStdlibStringUtilsSolution
          1. will throw a NullPointerException
        2. java -cp Lang/build/libs/Lang.jar org.devict.jlib.lang.ExampleStringUtils
          1. Won't throw a NullPointerException
    • SystemUtils - shortcuts for getting information about the system or the JVM that is running your application
      1. java -cp Lang/build/libs/Lang.jar org.devict.jlib.lang.ExampleSystemUtils
    • WordUtils - Word based formatting of strings
      1. java -cp Lang/build/libs/Lang.jar org.devict.jlib.lang.text.ExampleWordUtils
    • StrBuilder - StringBuilder/StringBuffer replacement
      1. java -cp Lang/build/libs/Lang.jar org.devict.jlib.lang.text.ExampleStrBuilder
    • Tuples - Simple pair and triple generic containers
      1. java -cp Lang/build/libs/Lang.jar org.devict.jlib.lang.tuple.ExampleTriple

Apache Commons Collections

  • Apache Commons Collections - Yet more things the Java Standard Library's collections should provide, but doesn't. (However they have added a bunch of stuff inspired by this library over the years see java.util.Collections)
    • CollectionUtils - helpful utility methods for dealing with collections
      1. java -cp Collections/build/libs/Collections.jar org.devict.jlib.collections.ExampleCollectionUtils
      2. java -cp Collections/build/libs/Collections.jar org.devict.jlib.collections.ExampleCaseInsensitiveMap
      3. java -cp Collections/build/libs/Collections.jar org.devict.jlib.collections.ExampleCollectionUtils
      4. java -cp Collections/build/libs/Collections.jar org.devict.jlib.collections.ExampleMultiValueMap
      5. java -cp Collections/build/libs/Collections.jar org.devict.jlib.collections.ExampleNonNullCaseInsensitiveMap

Apache Commons IO

  • More useful stuff that is missing from the Java standard libary. (However this too is less useful if you are using java 8 and NIO 2)

To Run

  1. java -cp IO/build/libs/IO.jar org.devict.io.ExampleIO

Apache Commons CSV

  • Great little CSV parser that supports many formats
    • Microsoft Excel
    • MySQL
    • RFC 4180
    • Others

To Run

  1. java -cp CSV/build/libs/CSV.jar org.devict.jlib.csv.ExampleStudentCSV

Apache Commons BeanUtils

  • Utility library for dealing with Java Beans

To run

  1. java -cp BeanUtils/build/libs/BeanUtils.jar org.devict.jlib.beanutils.CopyFromDifferentObjects

jopt-simple

  • Best CLI parser out there
  • Used by many projects
    • OpenJDK
    • Gradle
    • Others

To Run

  1. java -cp JOPTSimple/build/libs/JOPTSimple.jar org.devict.jlib.jopt.ExampleCLI
  2. java -cp JOPTSimple/build/libs/JOPTSimple.jar org.devict.jlib.jopt.ExampleCLI --help
  3. java -cp JOPTSimple/build/libs/JOPTSimple.jar org.devict.jlib.jopt.ExampleCLI -e http://www.google.com/ --username Prez --password 12345 --file test.txt -c config.ini

Apache PDFBox

Features

  • Create PDFs
  • Extract Text
  • Print using the Java Print API
  • Split & Merge
  • Fill Forms
  • Save as Image

To Run

  1. java -cp PDFBox/build/libs/PDFBox.jar org.devict.jlib.pdf.ExampleHelloPdf
  2. java -cp PDFBox/build/libs/PDFBox.jar org.devict.jlib.pdf.ExampleAddImage

Apache Avro

Apache Avro is very similar to Google's Protocol buffers, however it's main advantage is that it sends the schema the data was encoded with along with the message making it easier to evolve the schema over time. This is useful when building distributed systems using messaging middleware like Apache Kafka. When used with a Schema server you can build flexible processing systems that aren't as tightly coupled as they would be if you just shared a library of data classes for each application. Meaning you can upgrade applications slowly allowing for different teams to build separate parts of the system without perfect knowledge of the other applications.

The example provided here isn't as clear cut as the others because I wanted to show changing the schema slightly.

To Run

  1. java -cp Avro/build/libs/Avro.jar org.devict.jlib.avro.ExampleAvroWrite > out.avro #write with an older schema to out.avro
    1. This program uses the "newer" AdvancedEmployee schema to encode the message
  2. java -cp Avro/build/libs/Avro.jar org.devict.jlib.avro.ExampleAvroRead < out.avro #read with a newer schema from out.avro
    1. This program uses the "older" Employee schema to decode the message
  • Your Other option is to use the unix way of doing applications you can run
    • java -cp Avro/build/libs/Avro.jar org.devict.jlib.avro.ExampleAvroWrite | java -cp Avro/build/libs/Avro.jar org.devict.jlib.avro.ExampleAvroRead

Apache HTTP Components

An HTTP server that responds to any request with the time.

  1. java -cp HTTPComponents/build/libs/HTTPComponents.jar org.devict.jlib.http.server.HTTPServer
  2. curl -v -XGET http://localhost:8080/

An HTTP client that requests from a the above server and displays the time.

  1. java -cp HTTPComponents/build/libs/HTTPComponents.jar org.devict.jlib.http.client.HTTPClient
    1. make sure you are running the above server

Google Guava

Google's Guava library is the result of many internal and external Google projects that is useful as a base for many reusable components. Many of it's use cases seem more advanced than much of the stuff that available in Apache Commons.

To run the examples

  1. java -cp Guava/build/libs/Guava.jar org.devict.jlib.guava.ExampleEventBus
  2. java -cp Guava/build/libs/Guava.jar org.devict.jlib.guava.ExampleTable

Logback

This is the logging library I prefer right now primarily because it allows for configuration through Groovy and implements the Slf4j (simple logging facade for java) natively.

  • ExampleLogback
    • Logs to stdout and to /tmp/log/LogbackExample/LogbackExample.log
    • Logging is configured to roll once per day
      • can be configured to roll on size also (as well as other custom methods)

To run the example

  1. java -Dlog.dir=/tmp/LogbackExample -cp Logback/build/libs/Logback.jar org.devict.jlib.logback.ExampleLogback
    1. Note: -D is setting a Java system property (kind of like an environment variable, but only one that the JVM cares about)
    2. The log.dir system property is optional as the logging configuration does have a default. In this case /tmp/log, if you are on Windows this will blow up you should change it to something else if you are using Windows to run this example.

Joda-Time

Example on some possible uses for Joda-Time that make using Date's and Date Times much easier in Java

To run the example

  1. java -cp JodaTime/build/libs/JodaTime.jar org.devict.jlib.jodatime.CalculateOperationalPeriodBasedOnConfigurableDaysOfTheWeek
    1. Note: This example shows how to manipulate Joda-Time objects by calculating an operational week based on a start day of Wednesday and an end day of Tuesday

JGroups clustering

JGroups is a toolkit for reliable messaging. It can be used to create clusters whose nodes can send messages to each other.

JGroups Example

Terminalogy 
- Handler: The server that will broadcast messages to listening nodes throughout the cluster
- Agent: The node within the cluster that is listening for messages

To run the examples run these commands in 3 separate console windows

  1. java -Djava.net.preferIPv4Stack=true -cp JGroups/build/libs/JGroups.jar org.devict.jlib.cluster.JClusterHandler
    1. Starts up the broadcast server
  2. java -Djava.net.preferIPv4Stack=true -cp JGroups/build/libs/JGroups.jar org.devict.jlib.cluster.JClusterAgent
    1. Starts up a single instance of a receiver that receives messages from the server
  3. java -Djava.net.preferIPv4Stack=true -cp JGroups/build/libs/JGroups.jar org.devict.jlib.cluster.JClusterAgent
    1. Starts up a single instance of a receiver that receives messages from the server

JGroups Example Notes:

This JGroups structure is not the only option, but is just an illustration of how easy it is to build simple broadcast/receiving messages.

The example uses the default cluster configuration which is UDP. This may not scale as far as you may need, and may not cross collision domains, depends on how your network is configured.

Groovy embedded example

This illustrates how to embed a simple GroovyShell in an application to parse simple scripts. The provided example parses a list of maps defined in a String to a list of maps that the Java application can read.

To run the example

  1. java -cp Groovy/build/libs/Groovy.jar org.devict.jlib.groovy.ExampleEmbeddedGroovyStringToMap

Java Standard Library

This is stuf that is available in the standard library

  1. java -cp Stdlib/build/libs/Stdlib.jar org.devict.jlib.stdlib.ExampleDateTime
    1. shows an example of using the Java 8 time API doing simple comparisons and getting the Date Time from a file
  2. java -cp Stdlib/build/libs/Stdlib.jar org.devict.jlib.stdlib.ExampleStream
    1. simple java 8 streaming example
  3. java -cp Stdlib/build/libs/Stdlib.jar org.devict.jlib.stdlib.ExampleThreading
    1. simple threading example using the standard libraries threading facilities added in Java 5
  4. java -cp Stdlib/build/libs/Stdlib.jar org.devict.jlib.stdlib.ExampleFileWatcher
    1. example for using the Java 7 file watching utility added
    2. need to see where the temp directory is created and then create a file called watch.test in that directory.
      1. You can also add text to that file to cause the file changed even to fire
  5. java -cp Stdlib/build/libs/Stdlib.jar org.devict.jlibstdlib.ExampleURI
    1. exmaple showing some useful parsting of URI's using the java.net.URI class

Faker

This library is a port of Ruby's stympy/faker gem (as well as Perl's Data::Faker library) that generates fake data. It's useful when you're developing a new project and need some pretty data for showcase.

Faker Example

To run the example

  1. java -cp Faker/build/libs/Faker.jar org.devict.jlib.faker.ExampleFakerUsage