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java/org/apache/tomcat/util/scan/ReferenceCountedJar.java

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+/*
+ * 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 regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.tomcat.util.scan;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.URL;
+import java.util.jar.Manifest;
+
+import org.apache.tomcat.Jar;
+
+/**
+ * This class provides a wrapper around {@link Jar} that uses reference counting
+ * to close and re-create the wrapped {@link Jar} instance as required.
+ */
+public class ReferenceCountedJar implements Jar {
+
+    private final URL url;
+    private Jar wrappedJar;
+    private int referenceCount = 0;
+
+    public ReferenceCountedJar(URL url) throws IOException {
+        this.url = url;
+        open();
+    }
+
+
+    /*
+     * Note: Returns this instance so it can be used with try-with-resources
+     */
+    private synchronized ReferenceCountedJar open() throws IOException {
+        if (wrappedJar == null) {
+            wrappedJar = JarFactory.newInstance(url);
+        }
+        referenceCount++;
+        return this;
+    }
+
+
+    @Override
+    public synchronized void close() {
+        referenceCount--;
+        if (referenceCount == 0) {
+            wrappedJar.close();
+            wrappedJar = null;
+        }
+    }
+
+
+    @Override
+    public URL getJarFileURL() {
+        return url;
+    }
+
+
+    @Override
+    public InputStream getInputStream(String name) throws IOException {
+        try (ReferenceCountedJar jar = open()) {
+            return jar.wrappedJar.getInputStream(name);
+        }
+    }
+
+
+    @Override
+    public long getLastModified(String name) throws IOException {
+        try (ReferenceCountedJar jar = open()) {
+            return jar.wrappedJar.getLastModified(name);
+        }
+    }
+
+
+    @Override
+    public boolean exists(String name) throws IOException {
+        try (ReferenceCountedJar jar = open()) {
+            return jar.wrappedJar.exists(name);
+        }
+    }
+
+
+    @Override
+    public void nextEntry() {
+        try (ReferenceCountedJar jar = open()) {
+            jar.wrappedJar.nextEntry();
+        } catch (IOException ioe) {
+            throw new IllegalStateException(ioe);
+        }
+    }
+
+
+    @Override
+    public String getEntryName() {
+        try (ReferenceCountedJar jar = open()) {
+            return jar.wrappedJar.getEntryName();
+        } catch (IOException ioe) {
+            throw new IllegalStateException(ioe);
+        }
+    }
+
+
+    @Override
+    public InputStream getEntryInputStream() throws IOException {
+        try (ReferenceCountedJar jar = open()) {
+            return jar.wrappedJar.getEntryInputStream();
+        }
+    }
+
+
+    @Override
+    public String getURL(String entry) {
+        try (ReferenceCountedJar jar = open()) {
+            return jar.wrappedJar.getURL(entry);
+        } catch (IOException ioe) {
+            throw new IllegalStateException(ioe);
+        }
+    }
+
+
+    @Override
+    public Manifest getManifest() throws IOException {
+        try (ReferenceCountedJar jar = open()) {
+            return jar.wrappedJar.getManifest();
+        }
+    }
+
+
+    @Override
+    public void reset() throws IOException {
+        try (ReferenceCountedJar jar = open()) {
+            jar.wrappedJar.reset();
+        }
+    }
+
+
+    @Override
+    @Deprecated
+    public boolean entryExists(String name) throws IOException {
+        try (ReferenceCountedJar jar = open()) {
+            return jar.wrappedJar.entryExists(name);
+        }
+    }
+}