io.helidon.config.ValueResolvingFilter

public class ValueResolvingFilter extends Object implements ConfigFilter

A config filter that replaces all placeholders in a config value String with their corresponding values looked up from the config.

For example:

 message = "Hello ${name}!"
 name = "Joachim"

will be resolved as:

 message = "Hello Joachim!"

How to Activate This Filter

Use any of the following techniques to create a ValueResolvingFilter and use it for config look-ups.

Programmatically:
1. Invoke ConfigFilters.valueResolving() to get a builder for the filter.
2. Optionally, invoke the filter builder's failOnMissingReference method (see below).
3. Invoke the builder's build method to create the filter.
4. Then, on the Config.Builder being used to construct the Config instance, invoke Config.Builder#addFilter passing the just-created filter.
Implicitly: Create or edit the file io.helidon.config.ConfigFilter on the application's runtime classpath to contain this line:
```
 io.helidon.config.ValueResolvingFilter
```
The config system will then use the Java service loader mechanism to create and add this filter to every Config.Builder automatically.

By default, references to tokens that are not present do not cause retrievals to fail. You can customize this behavior in several ways.

If you use ConfigFilters.valueResolving() to get a builder for the filter, invoke the failOnMissingReference method on that builder before invoking the filter builder's build method.
If you use ConfigFilters.ValueResolvingBuilder.create(io.helidon.config.Config) to get the filter's builder, define this setting in the Config instance you pass to the from method:
```
 "config.value-resolving-filter.fail-on-missing-reference" = true
```
or false which is the default. This sets the behavior for the single filter created from that builder.
If you use the Java service loader mechanism to create ValueResolvingFilters for every Config.Builder, specify the following config setting in one of the config sources that composes the default config:
```
 "config.value-resolving-filter.fail-on-missing-reference" = true
```
or false which is the default. This sets the behavior for every ValueResolvingFilter created for which the failOnMissingReference value has not already been set, for example by invoking the ConfigFilters.valueResolving().failOnMissingReference() method.

Field Summary

Fields inherited from interface io.helidon.config.spi.ConfigFilter
PRIORITY
Constructor Summary

Constructors

Constructor

Description

ValueResolvingFilter()

Creates an instance of the filter with no explicit failOnMissing behavior set.

ValueResolvingFilter(boolean failOnMissingReference)

Creates an instance of filter with the specified behavior on missing references.
Method Summary

Modifier and Type

Method

Description

String

apply(Config.Key key, String stringValue)

Filters an elementary config value before it is made available to the application via the Config API.

void

init(Config config)

Initializes the filter using the Config instance which the filter will affect once Config.Builder.build completes.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Class ValueResolvingFilter