1 package org.apache.onami.spi.core;
2
3 /*
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
6 * distributed with this work for additional information
7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
11 *
12 * http://www.apache.org/licenses/LICENSE-2.0
13 *
14 * Unless required by applicable law or agreed to in writing,
15 * software distributed under the License is distributed on an
16 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17 * KIND, either express or implied. See the License for the
18 * specific language governing permissions and limitations
19 * under the License.
20 */
21
22 import static java.lang.String.format;
23
24 import java.util.Iterator;
25 import java.util.NoSuchElementException;
26
27 import com.google.inject.ProvisionException;
28
29 /**
30 * Lazy-loading iterator over the discovered classes.
31 *
32 * @param <S> The service type being loaded.
33 */
34 abstract class AbstractServiceClassIterator<S>
35 implements Iterator<Class<? extends S>>
36 {
37
38 /**
39 * The class or interface representing the service being loaded.
40 */
41 private final Class<S> service;
42
43 /**
44 * The class loader used to locate, load, and instantiate providers.
45 */
46 private final ClassLoader classLoader;
47
48 /**
49 * The pending providers Class names.
50 */
51 private Iterator<String> pending = null;
52
53 /**
54 * The reference to the next provider Class name.
55 */
56 private String nextName = null;
57
58 /**
59 * Creates a new Provider classes Iterator.
60 *
61 * @param service The Service being loaded.
62 * @param classLoader The ClassLoader used to load Provider classes.
63 */
64 public AbstractServiceClassIterator( Class<S> service, ClassLoader classLoader )
65 {
66 this.service = service;
67 this.classLoader = classLoader;
68 }
69
70 /**
71 * {@inheritDoc}
72 */
73 public final boolean hasNext()
74 {
75 if ( nextName != null )
76 {
77 return true;
78 }
79
80 while ( ( pending == null ) || !pending.hasNext() )
81 {
82 if ( !hasMorePendingNames() )
83 {
84 return false;
85 }
86 pending = getPendingNames();
87 }
88
89 nextName = pending.next();
90 return true;
91 }
92
93 /**
94 * Checks if there are still providers names to be loaded.
95 *
96 * @return true if there are still providers names to be loaded, false otherwise.
97 */
98 protected abstract boolean hasMorePendingNames();
99
100 /**
101 * Returns the iterator over next pending Providers names.
102 *
103 * @return the iterator over next pending Providers names.
104 */
105 protected abstract Iterator<String> getPendingNames();
106
107 /**
108 * {@inheritDoc}
109 */
110 public final Class<? extends S> next()
111 {
112 if ( !hasNext() )
113 {
114 throw new NoSuchElementException();
115 }
116 String className = nextName;
117 nextName = null;
118 try
119 {
120 Class<?> clazz = classLoader.loadClass( className );
121 if ( !service.isAssignableFrom( clazz ) )
122 {
123 throw new ProvisionException( format( "Provider '%s' is not assignable to Service '%s'",
124 className, service.getName() ) );
125 }
126 return clazz.asSubclass( service );
127 }
128 catch ( ClassNotFoundException e )
129 {
130 throw new ProvisionException( format( "Provider '%s' not found: %s", className, e.getMessage() ) );
131 }
132 catch ( ClassCastException e )
133 {
134 throw new ProvisionException( format( "Provider '%s' is not assignable to Service '%s'",
135 className, service.getName() ) );
136 }
137 }
138
139 /**
140 * {@inheritDoc}
141 */
142 public final void remove()
143 {
144 throw new UnsupportedOperationException();
145 }
146
147 }