[FLINK-3700] [core] Add 'Preconditions' utility class.

flink-core/src/main/java/org/apache/flink/util/Preconditions.java

@@ -0,0 +1,213 @@
+/*
+ * 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:https://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.
+ */
+
+// ----------------------------------------------------------------------------
+// This class is largely adapted from "com.google.common.base.Preconditions",
+// which is part of the "Guava" library.
+//
+// Because of frequent issues with dependency conflicts, this class was
+// added to the Flink code base to reduce dependency on Guava.
+// ----------------------------------------------------------------------------
+
+package org.apache.flink.util;
+
+import org.apache.flink.annotation.Internal;
+
+import javax.annotation.Nullable;
+
+/**
+ * A collection of static utility methods to validate input.
+ * 
+ * <p>This class is modelled after Google Guava's Preconditions class, and partly takes code
+ * from that class. We add this code to the Flink code base in order to reduce external
+ * dependencies.
+ */
+@Internal
+public final class Preconditions {
+
+ // ------------------------------------------------------------------------
+ // Null checks
+ // ------------------------------------------------------------------------
+
+ /**
+ * Ensures that the given object reference is not null.
+ * Upon violation, a {@code NullPointerException} with no message is thrown.
+ * 
+ * @param reference The object reference
+ * @return The object reference itself (generically typed).
+ * 
+ * @throws NullPointerException Thrown, if the passed reference was null.
+ */
+ public static <T> T checkNotNull(T reference) {
+ if (reference == null) {
+ throw new NullPointerException();
+ }
+ return reference;
+ }
+
+ /**
+ * Ensures that the given object reference is not null.
+ * Upon violation, a {@code NullPointerException} with the given message is thrown.
+ * 
+ * @param reference The object reference
+ * @param errorMessage The message for the {@code NullPointerException} that is thrown if the check fails.
+ * @return The object reference itself (generically typed).
+ *
+ * @throws NullPointerException Thrown, if the passed reference was null.
+ */
+ public static <T> T checkNotNull(T reference, @Nullable String errorMessage) {
+ if (reference == null) {
+ throw new NullPointerException(String.valueOf(errorMessage));
+ }
+ return reference;
+ }
+
+ /**
+ * Ensures that the given object reference is not null.
+ * Upon violation, a {@code NullPointerException} with the given message is thrown.
+ * 
+ * <p>The error message is constructed from a template and an arguments array, after
+ * a similar fashion as {@link String#format(String, Object...)}, but supporting only
+ * {@code %s} as a placeholder.
+ *
+ * @param reference The object reference
+ * @param errorMessageTemplate The message template for the {@code NullPointerException}
+ * that is thrown if the check fails. The template substitutes its
+ * {@code %s} placeholders with the error message arguments.
+ * @param errorMessageArgs The arguments for the error message, to be inserted into the
+ * message template for the {@code %s} placeholders.
+ * 
+ * @return The object reference itself (generically typed).
+ *
+ * @throws NullPointerException Thrown, if the passed reference was null.
+ */
+ public static <T> T checkNotNull(T reference,
+ @Nullable String errorMessageTemplate,
+ @Nullable Object... errorMessageArgs) {
+
+ if (reference == null) {
+ throw new NullPointerException(format(errorMessageTemplate, errorMessageArgs));
+ }
+ return reference;
+ }
+
+ // ------------------------------------------------------------------------
+ // Boolean Condition Checking
+ // ------------------------------------------------------------------------
+
+ /**
+ * Checks the given boolean condition, and throws an {@code IllegalArgumentException} if
+ * the condition is not met (evaluates to {@code false}).
+ *
+ * @param condition The condition to check
+ * 
+ * @throws IllegalArgumentException Thrown, if the condition is violated.
+ */
+ public static void checkArgument(boolean condition) {
+ if (!condition) {
+ throw new IllegalArgumentException();
+ }
+ }
+
+ /**
+ * Checks the given boolean condition, and throws an {@code IllegalArgumentException} if
+ * the condition is not met (evaluates to {@code false}). The exception will have the
+ * given error message.
+ *
+ * @param condition The condition to check
+ * @param errorMessage The message for the {@code IllegalArgumentException} that is thrown if the check fails.
+ * 
+ * @throws IllegalArgumentException Thrown, if the condition is violated.
+ */
+ public static void checkArgument(boolean condition, @Nullable Object errorMessage) {
+ if (!condition) {
+ throw new IllegalArgumentException(String.valueOf(errorMessage));
+ }
+ }
+
+ /**
+ * Checks the given boolean condition, and throws an {@code IllegalArgumentException} if
+ * the condition is not met (evaluates to {@code false}).
+ *
+ * @param condition The condition to check
+ * @param errorMessageTemplate The message template for the {@code IllegalArgumentException}
+ * that is thrown if the check fails. The template substitutes its
+ * {@code %s} placeholders with the error message arguments.
+ * @param errorMessageArgs The arguments for the error message, to be inserted into the
+ * message template for the {@code %s} placeholders.
+ * 
+ * @throws IllegalArgumentException Thrown, if the condition is violated.
+ */
+ public static void checkArgument(boolean condition,
+ @Nullable String errorMessageTemplate,
+ @Nullable Object... errorMessageArgs) {
+
+ if (!condition) {
+ throw new IllegalArgumentException(format(errorMessageTemplate, errorMessageArgs));
+ }
+ }
+
+
+ // ------------------------------------------------------------------------
+ // Utilities
+ // ------------------------------------------------------------------------
+
+ /**
+ * A simplified formatting method. Similar to {@link String#format(String, Object...)}, but
+ * with lower overhead (only String parameters, no locale, no format validation).
+ * 
+ * <p>This method is taken quasi verbatim from the Guava Preconditions class.
+ */
+ private static String format(@Nullable String template, @Nullable Object... args) {
+ final int numArgs = args == null ? 0 : args.length;
+ template = String.valueOf(template); // null -> "null"
+
+ // start substituting the arguments into the '%s' placeholders
+ StringBuilder builder = new StringBuilder(template.length() + 16 * numArgs);
+ int templateStart = 0;
+ int i = 0;
+ while (i < numArgs) {
+ int placeholderStart = template.indexOf("%s", templateStart);
+ if (placeholderStart == -1) {
+ break;
+ }
+ builder.append(template.substring(templateStart, placeholderStart));
+ builder.append(args[i++]);
+ templateStart = placeholderStart + 2;
+ }
+ builder.append(template.substring(templateStart));
+
+ // if we run out of placeholders, append the extra args in square braces
+ if (i < numArgs) {
+ builder.append(" [");
+ builder.append(args[i++]);
+ while (i < numArgs) {
+ builder.append(", ");
+ builder.append(args[i++]);
+ }
+ builder.append(']');
+ }
+
+ return builder.toString();
+ }
+
+ // ------------------------------------------------------------------------
+
+ /** Private constructor to prevent instantiation */
+ private Preconditions() {}
+}