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java/org/apache/tomcat/util/buf/StringUtils.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.buf;
+
+import java.util.Arrays;
+import java.util.Collection;
+
+/**
+ * Utility methods to build a separated list from a given set (not
+ * java.util.Set) of inputs and return that list as a string or append it to an
+ * existing StringBuilder. If the given set is null or empty, an empty string
+ * will be returned.
+ */
+public final class StringUtils {
+
+    private static final String EMPTY_STRING = "";
+
+    private StringUtils() {
+        // Utility class
+    }
+
+
+    public static String join(String[] array) {
+        if (array == null) {
+            return EMPTY_STRING;
+        }
+        return join(Arrays.asList(array));
+    }
+
+
+    public static void join(String[] array, char separator, StringBuilder sb) {
+        if (array == null) {
+            return;
+        }
+        join(Arrays.asList(array), separator, sb);
+    }
+
+
+    public static String join(Collection<String> collection) {
+        return join(collection, ',');
+    }
+
+
+    public static String join(Collection<String> collection, char separator) {
+        // Shortcut
+        if (collection == null || collection.isEmpty()) {
+            return EMPTY_STRING;
+        }
+
+        StringBuilder result = new StringBuilder();
+        join(collection, separator, result);
+        return result.toString();
+    }
+
+
+    public static void join(Iterable<String> iterable, char separator, StringBuilder sb) {
+        join(iterable, separator,
+                new Function<String>() {@Override public String apply(String t) { return t; }}, sb);
+    }
+
+
+    public static <T> void join(T[] array, char separator, Function<T> function,
+            StringBuilder sb) {
+        if (array == null) {
+            return;
+        }
+        join(Arrays.asList(array), separator, function, sb);
+    }
+
+
+    public static <T> void join(Iterable<T> iterable, char separator, Function<T> function,
+            StringBuilder sb) {
+        if (iterable == null) {
+            return;
+        }
+        boolean first = true;
+        for (T value : iterable) {
+            if (first) {
+                first = false;
+            } else {
+                sb.append(separator);
+            }
+            sb.append(function.apply(value));
+        }
+    }
+
+
+    public interface Function<T> {
+        public String apply(T t);
+    }
+}