When working on an AEM project, Sling Models provides several custom Sling Models injectors to aid injection of Sling objects, Sling object values, OSGI services, etc…
While using the injectors within in Sling Models, how do injectors invoke in order? Injectors are invoked in order, of their service ranking, from lowest to highest. If you are writing a custom injector, it is good practice to include service ranking.
Examples of the common injectors and their service ranking from the Apache Sling Models availiable injectors, injector-specific annotations, list (since version 1.1.0):
- @ScriptVariable, 1000
- @ValueMapValue, 2000
- @ChildResource, 3000
- @RequestAttribute, 4000
- @ResourcePath, 2500
- @OSGiService, 5000
- @Self, 2147483647 (Integer.MAX_VALUE)
- @SlingObject, 2147483647 (Integer.MAX_VALUE)
Example of the @OSGIService, injector:
An example below illustrates the @OSGIService, injector specific annotation, which here we understand that the Service Ranking is set to 5000.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 | /* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information... */ package org.apache.sling.models.impl.injectors; import java.lang.reflect.AnnotatedElement; import java.lang.reflect.Array; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; import java.util.ArrayList; import java.util.Arrays; import java.util.Collection; import java.util.Collections; import java.util.List; import org.apache.commons.lang3.StringUtils; import org.apache.sling.models.annotations.Filter; import org.apache.sling.models.annotations.injectorspecific.InjectionStrategy; import org.apache.sling.models.annotations.injectorspecific.OSGiService; import org.apache.sling.models.spi.AcceptsNullName; import org.apache.sling.models.spi.DisposalCallback; import org.apache.sling.models.spi.DisposalCallbackRegistry; import org.apache.sling.models.spi.Injector; import org.apache.sling.models.spi.injectorspecific.AbstractInjectAnnotationProcessor2; import org.apache.sling.models.spi.injectorspecific.InjectAnnotationProcessor2; import org.apache.sling.models.spi.injectorspecific.StaticInjectAnnotationProcessorFactory; import org.jetbrains.annotations.NotNull; import org.jetbrains.annotations.Nullable; import org.osgi.framework.BundleContext; import org.osgi.framework.Constants; import org.osgi.framework.InvalidSyntaxException; import org.osgi.framework.ServiceReference; import org.osgi.service.component.annotations.Activate; import org.osgi.service.component.annotations.Component; import org.slf4j.Logger; import org.slf4j.LoggerFactory; @Component(property=Constants.SERVICE_RANKING+":Integer=5000", service={Injector.class, StaticInjectAnnotationProcessorFactory.class, AcceptsNullName.class}) public class OSGiServiceInjector implements Injector, StaticInjectAnnotationProcessorFactory, AcceptsNullName { private static final Logger log = LoggerFactory.getLogger(OSGiServiceInjector.class); private BundleContext bundleContext; @Override public @NotNull String getName() { return "osgi-services"; } @Activate public void activate(BundleContext ctx) { this.bundleContext = ctx; } @Override public Object getValue(@NotNull Object adaptable, String name, @NotNull Type type, @NotNull AnnotatedElement element, @NotNull DisposalCallbackRegistry callbackRegistry) { return getValue(adaptable, name, type, element, callbackRegistry, bundleContext); } /** * * @param adaptable * @param name * @param type * @param element * @param callbackRegistry * @param modelContext * @return */ public Object getValue(@NotNull Object adaptable, String name, @NotNull Type type, @NotNull AnnotatedElement element, @NotNull DisposalCallbackRegistry callbackRegistry, @Nullable BundleContext modelContext) { OSGiService annotation = element.getAnnotation(OSGiService.class); String filterString = null; if (annotation != null) { if (StringUtils.isNotBlank(annotation.filter())) { filterString = annotation.filter(); } } else { Filter filter = element.getAnnotation(Filter.class); if (filter != null) { filterString = filter.value(); } } return getValue(adaptable, type, filterString, callbackRegistry, modelContext == null ? bundleContext : modelContext); } private <T> Object getService(Object adaptable, Class<T> type, String filter, DisposalCallbackRegistry callbackRegistry, BundleContext modelContext) { // cannot use SlingScriptHelper since it does not support ordering by service ranking due to https://issues.apache.org/jira/browse/SLING-5665 try { ServiceReference<?>[] refs = modelContext.getServiceReferences(type.getName(), filter); if (refs == null || refs.length == 0) { return null; } else { // sort by service ranking (lowest first) (see ServiceReference.compareTo) List<ServiceReference<?>> references = Arrays.asList(refs); Collections.sort(references); callbackRegistry.addDisposalCallback(new Callback(refs, modelContext)); return modelContext.getService(references.get(references.size() - 1)); } } catch (InvalidSyntaxException e) { log.error("invalid filter expression", e); return null; } } private <T> Object[] getServices(Object adaptable, Class<T> type, String filter, DisposalCallbackRegistry callbackRegistry, BundleContext modelContext) { // cannot use SlingScriptHelper since it does not support ordering by service ranking due to https://issues.apache.org/jira/browse/SLING-5665 try { ServiceReference<?>[] refs = modelContext.getServiceReferences(type.getName(), filter); if (refs == null || refs.length == 0) { return null; } else { // sort by service ranking (lowest first) (see ServiceReference.compareTo) List<ServiceReference<?>> references = Arrays.asList(refs); Collections.sort(references); // make highest service ranking being returned first Collections.reverse(references); callbackRegistry.addDisposalCallback(new Callback(refs, modelContext)); List<Object> services = new ArrayList<>(); for (ServiceReference<?> ref : references) { Object service = modelContext.getService(ref); if (service != null) { services.add(service); } } return services.toArray(); } } catch (InvalidSyntaxException e) { log.error("invalid filter expression", e); return null; } } private Object getValue(Object adaptable, Type type, String filterString, DisposalCallbackRegistry callbackRegistry, BundleContext modelContext) { if (type instanceof Class) { Class<?> injectedClass = (Class<?>) type; if (injectedClass.isArray()) { Object[] services = getServices(adaptable, injectedClass.getComponentType(), filterString, callbackRegistry, modelContext); if (services == null) { return null; } Object arr = Array.newInstance(injectedClass.getComponentType(), services.length); for (int i = 0; i < services.length; i++) { Array.set(arr, i, services[i]); } return arr; } else { return getService(adaptable, injectedClass, filterString, callbackRegistry, modelContext); } } else if (type instanceof ParameterizedType) { ParameterizedType ptype = (ParameterizedType) type; if (ptype.getActualTypeArguments().length != 1) { return null; } Class<?> collectionType = (Class<?>) ptype.getRawType(); if (!(collectionType.equals(Collection.class) || collectionType.equals(List.class))) { return null; } Class<?> serviceType = (Class<?>) ptype.getActualTypeArguments()[0]; Object[] services = getServices(adaptable, serviceType, filterString, callbackRegistry, modelContext); if (services == null) { return null; } return Arrays.asList(services); } else { log.warn("Cannot handle type {}", type); return null; } } private static class Callback implements DisposalCallback { private final ServiceReference<?>[] refs; private final BundleContext context; public Callback(ServiceReference<?>[] refs, BundleContext context) { this.refs = refs; this.context = context; } @Override public void onDisposed() { if (refs != null) { for (ServiceReference<?> ref : refs) { context.ungetService(ref); } } } } @Override public InjectAnnotationProcessor2 createAnnotationProcessor(AnnotatedElement element) { // check if the element has the expected annotation OSGiService annotation = element.getAnnotation(OSGiService.class); if (annotation != null) { return new OSGiServiceAnnotationProcessor(annotation); } return null; } private static class OSGiServiceAnnotationProcessor extends AbstractInjectAnnotationProcessor2 { private final OSGiService annotation; public OSGiServiceAnnotationProcessor(OSGiService annotation) { this.annotation = annotation; } @Override public InjectionStrategy getInjectionStrategy() { return annotation.injectionStrategy(); } @Override @SuppressWarnings("deprecation") public Boolean isOptional() { return annotation.optional(); } } } |
The source code can be found from the Github repository, Apache Sling Models Implementation, here.
The official documentation for the Sling Models available injector’s service ranking status can be found here.
