org.yarnandtail.andhow.load.std

Class StdSysPropLoader

java.lang.Object

org.yarnandtail.andhow.load.BaseLoader

org.yarnandtail.andhow.load.BaseMapLoader

org.yarnandtail.andhow.load.std.StdSysPropLoader

All Implemented Interfaces:

Loader, ReadLoader, StandardLoader

public class StdSysPropLoader
extends BaseMapLoader
implements StandardLoader

Reads the Java system properties and loads the value for any system property with a name matching a Property.

Position in Standard Loading Order, first to last

• StdFixedValueLoader
• StdMainStringArgsLoader
• StdSysPropLoader <-- This loader
• StdEnvVarLoader
• StdJndiLoader
• StdPropFileOnFilesystemLoader
• StdPropFileOnClasspathLoader

Property value loading is based on a 'first win' strategy, so the first loader to find a non-null value for a property sets the value.

Typical Use Case

An application might receive all or some of its configuration from Java system properties that are set when the JVM starts up. Java system properties can be set in a startup script, which could be customized for each environment. This provides a relatively easy way for deployment automation or system administrators to control application configuration values across many servers.

Basic Behaviors

• Trims String values: Yes The Trimmer configured for a String based property will be applied as the value is loaded. For most String-based properties this defaults to QuotedSpacePreservingTrimmer. Non-String values are always trimmed to null.
• Complains about unrecognized properties: No

Loader Details and Configuration

This loader loads properties from the values it finds in java.lang.System.getProperties() at the time AndHow is initialized. Over the lifecycle of the JVM, the values of system properties can change so they may not reflect the values AndHow has loaded. However, once loaded, AndHow property values never change. It is also possible for application code to add to or modify system properties after the JVM starts up and before AndHow initializes, potentially resulting in a AndHow's configuration not matching the values set in a JVM startup script.

For FlgProp properties (true/false flags), the StdSysPropLoader will set the Property's value to true if a matching environment variable is found, even if the value of the property is empty. System properties can be cleared via java.lang.System.clearProperty(name), which is how a flag value could be unset prior to AndHow loading.

Passing system properties on command line looks like this:

java -Dfull.name.of.MY_PROPERTY=someValue -jar MyJarName.jar

This is a Standard Loader

Like all StandardLoader's, this loader is intended to be auto-created by AndHow. The set of standard loaders and their order can bet set via the AndHowConfiguration.setStandardLoaders() methods. Other loaders which don't implement the StandardLoader interface can be inserted into the load order via the AndHowConfiguration.insertLoaderBefore/After().

Field Summary

Fields inherited from class org.yarnandtail.andhow.load.BaseMapLoader

unknownPropertyAProblem

Constructor Summary

Constructors

Constructor and Description
StdSysPropLoader() There is no reason to use the constructor in production application code because AndHow creates a single instance on demand at runtime.

Method Summary

Modifier and Type	Method and Description
String	getLoaderType() The type of the loader, such as JNDI, PropertyFile, SystemProperty, etc..
String	getSpecificLoadDescription() For this particular load, where was info loaded from? This may vary from run to run based on config params.
boolean	isTrimmingRequiredForStringValues() If true, values for string properties are trimmed by the Trimmer of the property they are associated with.
LoaderValues	load(PropertyConfigurationInternal runtimeDef, LoaderEnvironment environment, ValidatedValuesWithContext existingValues) Builds up a list of LoaderValues by loading property values from a configuration source.

Methods inherited from class org.yarnandtail.andhow.load.BaseMapLoader

getLoaderDialect, isFlaggable, isUnknownPropertyAProblem, load, setUnknownPropertyAProblem

Methods inherited from class org.yarnandtail.andhow.load.BaseLoader

attemptToAdd, attemptToAdd, attemptToAdd, attemptToAddIfNotDuplicate, createValue, findDuplicateProperty, getClassConfig, getConfigSamplePrinter, getInstanceConfig, mapNametoProperty, releaseResources

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface org.yarnandtail.andhow.api.Loader

getClassConfig, getConfigSamplePrinter, getInstanceConfig, getLoaderDialect, isFlaggable, releaseResources

Constructor Detail

StdSysPropLoader

public StdSysPropLoader()

There is no reason to use the constructor in production application code because AndHow creates a single instance on demand at runtime.

Method Detail

load

public LoaderValues load(PropertyConfigurationInternal runtimeDef,
                         LoaderEnvironment environment,
                         ValidatedValuesWithContext existingValues)

Description copied from interface: Loader

Builds up a list of LoaderValues by loading property values from a configuration source.

Loaders find and load values and associate them with the correct Property. If there is a problem while doing that, they register one or more LoaderProblems in the returned LoaderValues.

Validation of Property values is not Loader's responsibility and will be handled outside this method.

Specified by:

load in interface Loader

Parameters:

runtimeDef - The definition of all known Properties and naming metadata.

environment - The environment (System Props, Env vars, fixed values) as known to the Loader.

existingValues - The values already set by prior loaders, which may configure the behavior of this loader.

Returns:

The Property values loaded by this loader and/or the problems discovered while attempting to load those Property values.

getSpecificLoadDescription

public String getSpecificLoadDescription()

Description copied from interface: Loader

For this particular load, where was info loaded from? This may vary from run to run based on config params. For instance, The PropFileLoader will look multiple places to find a properties file. This method should return the actual location it was found. Assume the text is prefixed with "This loader loaded from: ". An example would be "/home/user/config/my-props.properties" No ending punctuation should be used.

Specified by:

getSpecificLoadDescription in interface Loader

Overrides:

getSpecificLoadDescription in class BaseMapLoader

Returns:

isTrimmingRequiredForStringValues

public boolean isTrimmingRequiredForStringValues()

Description copied from interface: Loader

If true, values for string properties are trimmed by the Trimmer of the property they are associated with. If false, no trimming is done. Non-String type property values (like Integer or Date type values) are not affected by this. Loaders that read from text files need to trim values to separate white space and carriage returns from the value. Loaders that read from more tightly defined sources, like reading properties from java.lang.System.getProperties(), can assume that trimming has already happened.

Specified by:

isTrimmingRequiredForStringValues in interface Loader

Overrides:

isTrimmingRequiredForStringValues in class BaseMapLoader

Returns:

getLoaderType

public String getLoaderType()

Description copied from interface: Loader

The type of the loader, such as JNDI, PropertyFile, SystemProperty, etc.. The actual return value is arbitrary, but should be consistent between loaders of the same type. The values returned by getLoaderType and getLoaderDialect are used to removed duplicate loader types when printing sample files. If two loader instances are of the same type and dialect, only one will print the sample file.

Specified by:

getLoaderType in interface Loader

Overrides:

getLoaderType in class BaseMapLoader

Returns:

Must never returns null.