188 lines
7.4 KiB
Java
188 lines
7.4 KiB
Java
/*
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* Copyright (C) 2013 The Guava Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
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* in compliance with the License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software distributed under the License
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* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
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* or implied. See the License for the specific language governing permissions and limitations under
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* the License.
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*/
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package com.google.common.base;
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import static com.google.common.base.Preconditions.format;
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import javax.annotation.Nullable;
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import com.google.common.annotations.Beta;
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import com.google.common.annotations.GwtCompatible;
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/**
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* Static convenience methods that serve the same purpose as Java language
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* <a href=
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* "http://docs.oracle.com/javase/7/docs/technotes/guides/language/assert.html">
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* assertions</a>, except that they are always enabled. These methods should be
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* used instead of Java assertions whenever there is a chance the check may fail
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* "in real life". Example:
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*
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* <pre>
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* {
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* @code
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*
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* Bill bill = remoteService.getLastUnpaidBill();
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*
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* // In case bug 12345 happens again we'd rather just die
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* Verify.verify(bill.status() == Status.UNPAID, "Unexpected bill status: %s", bill.status());
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* }
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* </pre>
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*
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* <h3>Comparison to alternatives</h3>
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*
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* <p>
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* <b>Note:</b> In some cases the differences explained below can be subtle.
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* When it's unclear which approach to use, <b>don't worry</b> too much about
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* it; just pick something that seems reasonable and it will be fine.
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*
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* <ul>
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* <li>If checking whether the <i>caller</i> has violated your method or
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* constructor's contract (such as by passing an invalid argument), use the
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* utilities of the {@link Preconditions} class instead.
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*
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* <li>If checking an <i>impossible</i> condition (which <i>cannot</i> happen
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* unless your own class or its <i>trusted</i> dependencies is badly broken),
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* this is what ordinary Java assertions are for. Note that assertions are not
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* enabled by default; they are essentially considered "compiled comments."
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*
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* <li>An explicit {@code if/throw} (as illustrated above) is always acceptable;
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* we still recommend using our {@link VerifyException} exception type. Throwing
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* a plain {@link RuntimeException} is frowned upon.
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*
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* <li>Use of {@link java.util.Objects#requireNonNull(Object)} is generally
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* discouraged, since {@link #verifyNotNull(Object)} and
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* {@link Preconditions#checkNotNull(Object)} perform the same function with
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* more clarity.
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* </ul>
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*
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* <h3>Warning about performance</h3>
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*
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* <p>
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* Remember that parameter values for message construction must all be computed
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* eagerly, and autoboxing and varargs array creation may happen as well, even
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* when the verification succeeds and the message ends up unneeded.
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* Performance-sensitive verification checks should continue to use usual form:
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*
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* <pre>
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* {
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* @code
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*
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* Bill bill = remoteService.getLastUnpaidBill();
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* if (bill.status() != Status.UNPAID) {
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* throw new VerifyException("Unexpected bill status: " + bill.status());
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* }
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* }
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* </pre>
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*
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* <h3>Only {@code %s} is supported</h3>
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*
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* <p>
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* As with {@link Preconditions} error message template strings, only the
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* {@code "%s"} specifier is supported, not the full range of
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* {@link java.util.Formatter} specifiers. However, note that if the number of
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* arguments does not match the number of occurrences of {@code "%s"} in the
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* format string, {@code Verify} will still behave as expected, and will still
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* include all argument values in the error message; the message will simply not
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* be formatted exactly as intended.
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*
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* <h3>More information</h3>
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*
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* See <a href=
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* "http://code.google.com/p/guava-libraries/wiki/ConditionalFailuresExplained">Conditional
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* failures explained</a> in the Guava User Guide for advice on when this class
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* should be used.
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*
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* @since 17.0
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*/
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@Beta
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@GwtCompatible
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public final class Verify {
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/**
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* Ensures that {@code expression} is {@code true}, throwing a
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* {@code VerifyException} with no message otherwise.
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*/
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public static void verify(boolean expression) {
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if (!expression) {
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throw new VerifyException();
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}
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}
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/**
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* Ensures that {@code expression} is {@code true}, throwing a
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* {@code VerifyException} with a custom message otherwise.
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*
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* @param expression a boolean expression
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* @param errorMessageTemplate a template for the exception message should the
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* check fail. The message is formed by replacing
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* each {@code %s} placeholder in the template with
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* an argument. These are matched by position - the
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* first {@code %s} gets
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* {@code errorMessageArgs[0]}, etc. Unmatched
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* arguments will be appended to the formatted
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* message in square braces. Unmatched placeholders
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* will be left as-is.
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* @param errorMessageArgs the arguments to be substituted into the message
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* template. Arguments are converted to strings
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* using {@link String#valueOf(Object)}.
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* @throws VerifyException if {@code expression} is {@code false}
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*/
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public static void verify(boolean expression, @Nullable String errorMessageTemplate,
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@Nullable Object... errorMessageArgs) {
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if (!expression) {
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throw new VerifyException(format(errorMessageTemplate, errorMessageArgs));
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}
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}
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/**
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* Ensures that {@code reference} is non-null, throwing a
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* {@code VerifyException} with a default message otherwise.
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*
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* @return {@code reference}, guaranteed to be non-null, for convenience
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*/
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public static <T> T verifyNotNull(@Nullable T reference) {
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return verifyNotNull(reference, "expected a non-null reference");
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}
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/**
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* Ensures that {@code reference} is non-null, throwing a
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* {@code VerifyException} with a custom message otherwise.
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*
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* @param errorMessageTemplate a template for the exception message should the
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* check fail. The message is formed by replacing
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* each {@code %s} placeholder in the template with
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* an argument. These are matched by position - the
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* first {@code %s} gets
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* {@code errorMessageArgs[0]}, etc. Unmatched
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* arguments will be appended to the formatted
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* message in square braces. Unmatched placeholders
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* will be left as-is.
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* @param errorMessageArgs the arguments to be substituted into the message
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* template. Arguments are converted to strings
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* using {@link String#valueOf(Object)}.
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* @return {@code reference}, guaranteed to be non-null, for convenience
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*/
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public static <T> T verifyNotNull(@Nullable T reference, @Nullable String errorMessageTemplate,
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@Nullable Object... errorMessageArgs) {
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verify(reference != null, errorMessageTemplate, errorMessageArgs);
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return reference;
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}
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// TODO(kevinb): consider <T> T verifySingleton(Iterable<T>) to take over for
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// Iterables.getOnlyElement()
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private Verify() {
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}
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}
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