1 /***********************************************************************
2  * Copyright (c) 2013-2025 General Atomics Integrated Intelligence, Inc.
3  * All rights reserved. This program and the accompanying materials
4  * are made available under the terms of the Apache License, Version 2.0
5  * which accompanies this distribution and is available at
6  * https://www.apache.org/licenses/LICENSE-2.0
7  ***********************************************************************/
8 
9 package org.locationtech.geomesa.utils.classpath
10 
11 import com.typesafe.scalalogging.LazyLogging
12 
13 import scala.reflect.ClassTag
14 
15 /**
16   * Scala SPI loader helper
17   */
18 object ServiceLoader extends LazyLogging {
19 
20   import scala.collection.JavaConverters._
21 
22   /**
23    * Load all services
24    *
25    * @param loader optional classloader to use
26    * @param ct classtag
27    * @tparam T service type
28    * @return list of services
29    */
30   def load[T](loader: Option[ClassLoader] = None)(implicit ct: ClassTag[T]): List[T] = {
31     // check if the current class is a child of the context classloader
32     // this fixes service loading in Accumulo's per-namespace classpaths
33     val clas = ct.runtimeClass.asInstanceOf[Class[T]]
34     val ldr = loader.getOrElse {
35       def chain(cl: ClassLoader): Stream[ClassLoader] =
36         if (cl == null) { Stream.empty } else { cl #:: chain(cl.getParent) }
37       val ccl = Thread.currentThread().getContextClassLoader
38       if (ccl == null || chain(clas.getClassLoader).contains(ccl)) {
39         clas.getClassLoader
40       } else {
41         logger.warn(s"Using a context ClassLoader that does not contain the class to load (${clas.getName}): $ccl")
42         ccl
43       }
44     }
45     java.util.ServiceLoader.load(clas, ldr).asScala.toList
46   }
47 
48   /**
49     * Load a service. If there is not exactly 1 implementation found, throws an exception
50     *
51     * @param ct classtag
52     * @tparam T service type
53     * @throws IllegalStateException if there is not exactly 1 service found
54     * @return service
55     */
56   @throws[IllegalStateException]
57   def loadExactlyOne[T](loader: Option[ClassLoader] = None)(implicit ct: ClassTag[T]): T = {
58     val all = load[T](loader)
59     if (all.lengthCompare(1) != 0) {
60       throw new IllegalStateException(s"Expected 1 instance of ${ct.runtimeClass.getName} but found ${all.length}")
61     }
62     all.head
63   }
64 
65   /**
66     * Load a service. If there is not exactly 0 or 1 implementations found, throws an exception
67     *
68     * @param ct classtag
69     * @tparam T service type
70     * @throws IllegalStateException if there is not exactly 0 or 1 service found
71     * @return service, if found
72     */
73   @throws[IllegalStateException]
74   def loadAtMostOne[T](loader: Option[ClassLoader] = None)(implicit ct: ClassTag[T]): Option[T] = {
75     val all = load[T](loader)
76     if (all.lengthCompare(1) > 0) {
77       throw new IllegalStateException(s"Expected 0 or 1 instances of ${ct.runtimeClass.getName} but found ${all.length}")
78     }
79     all.headOption
80   }
81 }