Pull cacheinvalidations code directory into chromium repo.

third_party/cacheinvalidation/src/java/com/google/ipc/invalidation/util/LazyString.java

+/*
+ * Copyright 2011 Google Inc.
+ *
+ * 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.ipc.invalidation.util;
+
+import java.util.Collection;
+
+
+/**
+ * Utilities to enable creation of lazy strings, where the instantiation of the string is delayed
+ * so that, e.g., log messages that aren't printed have reduced overhead.
+ */
+public class LazyString {
+
+  /** Receiver formatting objects using {@link Object#toString()}. */
+  public static final LazyStringReceiver<Object> OBJECT_RECEIVER =
+      new LazyStringReceiver<Object>() {
+        @Override
+        public void appendToBuilder(TextBuilder builder, Object element) {
+          builder.append(element);
+        }
+      };
+
+  /**
+   * Receiver appending an {@code element} to the given {@code builder}. Implementations may assume
+   * the builder and element are not {@code null}.
+   */
+  public interface LazyStringReceiver<T> {
+    void appendToBuilder(TextBuilder builder, T element);
+  }
+
+  /**
+   * Given an {@code element} to be logged lazily, returns null if the object is null. Otherwise,
+   * return an object that would convert it to a string using {@code builderFunction}. I.e., this
+   * method will call {@code builderFunction} with a new {@link TextBuilder} and provided
+   * {@code element} and return the string created with it.
+   */
+  public static <T> Object toLazyCompactString(final T element,
+      final LazyStringReceiver<T> builderFunction) {
+    if (element == null) {
+      return null;
+    }
+    return new Object() {
+      @Override public String toString() {
+        TextBuilder builder = new TextBuilder();
+        builderFunction.appendToBuilder(builder, element);
+        return builder.toString();
+      }
+    };
+  }
+
+  /**
+   * Returns an object that converts the given {@code elements} array into a debug string when
+   * {@link Object#toString} is called using
+   * {@link #appendElementsToBuilder(TextBuilder, Object[], LazyStringReceiver)}.
+   */
+  public static <T> Object toLazyCompactString(final T[] elements,
+      final LazyStringReceiver<? super T> elementReceiver) {
+    if ((elements == null) || (elements.length == 0)) {
+      return null;
+    }
+    return new Object() {
+      @Override public String toString() {
+        return appendElementsToBuilder(new TextBuilder(), elements, elementReceiver).toString();
+      }
+    };
+  }
+
+  /**
+   * Returns an object that converts the given {@code elements} collection into a debug string when
+   * {@link Object#toString} is called using
+   * {@link #appendElementsToBuilder(TextBuilder, Object[], LazyStringReceiver)}.
+   */
+  public static <T> Object toLazyCompactString(final Collection<T> elements,
+      final LazyStringReceiver<? super T> elementReceiver) {
+    if ((elements == null) || elements.isEmpty()) {
+      return null;
+    }
+    return new Object() {
+      @Override public String toString() {
+        return appendElementsToBuilder(new TextBuilder(), elements, elementReceiver).toString();
+      }
+    };
+  }
+
+  /**
+   * Appends {@code elements} formatted using {@code elementReceiver} to {@code builder}. Elements
+   * are comma-separated.
+   */
+  public static <T> TextBuilder appendElementsToBuilder(TextBuilder builder, T[] elements,
+      LazyStringReceiver<? super T> elementReceiver) {
+    if (elements == null) {
+      return builder;
+    }
+    for (int i = 0; i < elements.length; i++) {
+      if (i != 0) {
+        builder.append(", ");
+      }
+      T element = elements[i];
+      if (element != null) {
+        elementReceiver.appendToBuilder(builder, element);
+      }
+    }
+    return builder;
+  }
+
+  /**
+   * Appends {@code elements} formatted using {@code elementReceiver} to {@code builder}. Elements
+   * are comma-separated.
+   */
+  public static <T> TextBuilder appendElementsToBuilder(TextBuilder builder,
+      Iterable<T> elements, LazyStringReceiver<? super T> elementReceiver) {
+    if (elements == null) {
+      return builder;
+    }
+    boolean first = true;
+    for (T element : elements) {
+      if (first) {
+        first = false;
+      } else {
+        builder.append(", ");
+      }
+      if (element != null) {
+        elementReceiver.appendToBuilder(builder, element);
+      }
+    }
+    return builder;
+  }
+
+  private LazyString() {  // To prevent instantiation.
+  }
+}