Move Url utility class to restapi package

This is a trivial relocation of code to support a new type
safe definition for id strings in views.

Change-Id: I9b73786a58763813cd9ff9877f5aac0adb1333f3

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/restapi/Url.java

@@ -0,0 +1,65 @@
+// Copyright (C) 2012 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.extensions.restapi;
+
+import java.io.UnsupportedEncodingException;
+import java.net.URLDecoder;
+import java.net.URLEncoder;
+
+/** URL related utility functions. */
+public final class Url {
+  /**
+   * Encode a path segment, escaping characters not valid for a URL.
+   * <p>
+   * The following characters are not escaped:
+   * <ul>
+   * <li>{@code a..z, A..Z, 0..9}
+   * <li>{@code . - * _}
+   * </ul>
+   * <p>
+   * ' ' (space) is encoded as '+'.
+   * <p>
+   * All other characters (including '/') are converted to the triplet "%xy"
+   * where "xy" is the hex representation of the character in UTF-8.
+   *
+   * @param component a string containing text to encode.
+   * @return a string with all invalid URL characters escaped.
+   */
+  public static String encode(String component) {
+    if (component != null) {
+      try {
+        return URLEncoder.encode(component, "UTF-8");
+      } catch (UnsupportedEncodingException e) {
+        throw new RuntimeException("JVM must support UTF-8", e);
+      }
+    }
+    return null;
+  }
+
+  /** Decode a URL encoded string, e.g. from {@code "%2F"} to {@code "/"}. */
+  public static String decode(String str) {
+    if (str != null) {
+      try {
+        return URLDecoder.decode(str, "UTF-8");
+      } catch (UnsupportedEncodingException e) {
+        throw new RuntimeException("JVM must support UTF-8", e);
+      }
+    }
+    return null;
+  }
+
+  private Url() {
+  }
+}