69. Placeholder Service¶

The Placeholder Service API provides components a way to resolve variables in strings, known as placeholders, whose values are managed outside the component itself. For example a datum data source plugin could use the Placeholder Service to support resolving placeholders in a configurable Source ID property.

SolarNode provides a Placeholder Service implementation that resolves both dynamic placeholders from the Settings Database (using the setting namespace placeholder), and static placeholders from a configurable file or directory location.

69.1 Use¶

Call the resolvePlaceholders(s, parameters) method to resolve all placeholders on the String s. The parameters argument can be used to provide additional placeholder values, or you can pass just pass null to rely solely on the placeholders available in the service already.

69.1.1 Example¶

Here is an imaginary class that is constructed with an optional PlaceholderService, and then when the go() method is called uses that to resolve placeholders in the string {building}/temp and return the result:

package com.example;

import net.solarnetwork.node.service.PlaceholderService;
import net.solarnetwork.service.OptionalService;

public class MyComponent {

    private final OptionalService<PlaceholderService> placeholderService;

    public MyComponent(OptionalService<PlaceholderService> placeholderService) {
        super();
        this.placeholderService = placeholderService;
    }

    public String go() {
        return PlaceholderService.resolvePlaceholders(placeholderService,
                "{building}/temp", null);
    }
}

69.2 Blueprint¶

To use the Placeholder Service in your component, add either an Optional Service or explicit reference to your plugin's Blueprint XML file like this (depending on what your plugin requires):

<bean id="placeholderService" class="net.solarnetwork.common.osgi.service.DynamicServiceTracker">
    <argument ref="bundleContext"/>
    <property name="serviceClassName" value="net.solarnetwork.node.service.PlaceholderService"/>
    <property name="sticky" value="true"/>
</bean>

<reference id="placeholderService" interface="net.solarnetwork.node.service.PlaceholderService"/>

Then inject that service into your component's <bean>, for example:

<bean id="myComponent" class="com.example.MyComponent">
    <argument ref="placeholderService">
</bean>

69.3 Configuration¶

The Placeholder Service supports the following configuration properties in the net.solarnetwork.node.core namespace: