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Introducing AndHow's new Logo

AndHow's new logo

Many thanks to everyone who participated in the AndHow logo contest in October. All six logo entries were solid, but Carl Schroedl's entry was a clear winner. Carl's logo looks a bit like a swiss army knife or bottle opener, reflecting the utility aspect of AndHow. The logo also combines an ampersand (&) and a question mark into one simple and clever symbol. Well done Carl!

Andhow Visual

AndHow! strong.valid.simple.AppConfiguration

AndHow is an easy to use configuration framework with strong typing and detailed validation for web apps, command line or any application environment.

Learn more at the AndHow main site

Key Features

Questions / Discussion / Contact

Join the discussion on the user forum or the Slack group (See details on the Join page).

Use it via Maven (available on Maven Central)


AndHow can be used in projects with Java 8 and above, however, Java 9 and above have some restrictions

Complete Usage Example

More usage examples and documentation are available at the AndHow main site

package org.simple;

import org.yarnandtail.andhow.AndHow;

public class GettingStarted {

    public final static IntProp COUNT_DOWN_START = IntProp.builder().mustBeNonNull()

    private final static StrProp LAUNCH_CMD = StrProp.builder().mustBeNonNull()
            .desc("What to say when its time to launch")

    public String launch() {
        String launch = "";

        for (int i = COUNT_DOWN_START.getValue(); i >= 1; i--) {
            launch = launch += i + "...";

        return launch + LAUNCH_CMD.getValue();

    public static void main(String[] args) {
        AndHow.findConfig().setCmdLineArgs(args);   //3 Optional

        System.out.println( new GettingStarted().launch() );
        System.out.println( LAUNCH_CMD.getValue().replace("Go", "Gone") );

Section //1 : Declaring AndHow Properties

Properties must be final static, but may be private or any other scope. builder methods simplify adding validation, description, defaults and other metadata. Properties are strongly typed, so default values and validation are type specific, e.g., StrProp has Regex validation while the IntProp has GreaterThan / LessThan rules available.

Section //2 : Using AndHow Properties

AndHow Properties are used just like static final constants with an added .getValue() tacked on. Strong typing means that calling COUNT_DOWN_START.getValue() returns an Integer while calling LAUNCH_CMD.getValue() returns a String.

An AndHow Property (and its value) can be accessed anywhere it is visible. COUNT_DOWN_START is public in a public class, so it could be used anywhere, while LAUNCH_CMD is private. AndHow Properties are always static, so they can be accessed in both static and instance methods, just like this example shows.

Section //3 : Accepting Command Line Arguments

If an application needs command line arguments (CLAs), just pass them to AndHow at startup as this example shows. Properties are referred to using 'dot notation', e.g.:

java -jar GettingStarted.jar org.simple.GettingStarted.LAUNCH_CMD=GoManGo

If you don't need to accept CLA's, you can leave line //3 out - AndHow will initialize and startup without any explicit init method when the first Property is accessed.

How do I actually configure some values?

We're getting there. The example has defaults for each property so with no other configuration available, the main method uses the defaults and prints:


Things are more interesting if the default values are removed from the code above:

public final static IntProp COUNT_DOWN_START = IntProp.builder().mustBeNonNull()
        .mustBeGreaterThanOrEqualTo(1).build();  //default removed

private final static StrProp LAUNCH_CMD = StrProp.builder().mustBeNonNull()
        .mustMatchRegex(".*Go.*").build();  //default removed

Both properties must be non-null, so removing the defaults causes the validation rules to be violated at startup. Here is an excerpt from the console when that happens:

Drat! There were AndHow startup errors.
Sample configuration files will be written to: '/some_local_tmp_directory/andhow-samples/'
Property org.simple.GettingStarted.COUNT_DOWN_START: This Property must be non-null
Property org.simple.GettingStarted.LAUNCH_CMD: This Property must be non-null

AndHow does validation at startup for all properties in the entire application. Properties, even those defined in 3rd party jars, are discovered and values for them are loaded and validated.
If validation fails (as it did above), AndHow throws a RuntimeException to stop application startup and uses property metadata to generate specific error messages and (helpfully) sample configuration files. Here is an excerpt of the Java Properties file created when the code above failed validation:

# ######################################################################
# Property Group org.simple.GettingStarted

# COUNT_DOWN_START (Integer) NON-NULL - Start the countdown from this number
# The property value must be greater than or equal to 1
org.simple.GettingStarted.COUNT_DOWN_START = [Integer]

# LAUNCH_CMD (String) NON-NULL - What to say when its time to launch
# The property value must match the regex expression '.*Go.*'
org.simple.GettingStarted.LAUNCH_CMD = [String]

AndHow uses all of the provided metadata to create a detailed and well commented configuration file for your project.
Insert some real values into that file and place it on your classpath at / and it will automatically be discovered and loaded at startup. By default, AndHow discovers and loads configuration from seven common sources.
The default list of configuration loading, in order, is:

  1. Fixed values (explicitly set in code for AndHow to use)
  2. String[] arguments from the static void main() method
  3. System Properties (Like the one auto-generated above)
  4. Environmental Variables
  5. JNDI
  6. Java properties file on the filesystem (path must be specified)
  7. Java properties file on the classpath (defaults to /

Property values are set on a first-win basis, so if a property is set as fixed value, that will take precedence over values passed in to the main method.
Values passed to the main method take precedence over system properties as so on.

For more examples and documentation, visit the AndHow main site