```

/// tip

Here we use <a href="https://docs.python.org/3/library/time.html#time.perf_counter" class="external-link" target="_blank">`time.perf_counter()`</a> instead of `time.time()` because it can be more precise for these use cases. 🤓

///

## Other middlewares

You can later read more about other middlewares in the [Advanced User Guide: Advanced Middleware](../advanced/middleware.md){.internal-link target=_blank}.

 *       other code to use these forms too. Only the most typically used JUnit assertion methods are
 *       defined this way, but enough to live with.
 *   <li>If you override {@link #setUp} or {@link #tearDown}, make sure to invoke {@code
 *       super.setUp} and {@code super.tearDown} within them. These methods are used to clear and
 *       check for thread assertion failures.

 * part of the open-source <a href="https://github.com/google/guava">Guava</a> library.
 *
 * <p>The classes in this package include:
 *
 * <h2>Immutable collections</h2>
 *
 * These are collections whose contents will never change. They also offer a few additional
 * guarantees (see {@link ImmutableCollection} for details). Implementations are available for both

            return builder.build(KEY_TO_STRING_LOADER);
          }
        });
  }

  public void testContainsKeyAndValue() {
    for (LoadingCache<Key, String> cache : caches()) {
      // maintain strong refs so these won't be collected, regardless of cache's key/value strength
      Key key = new Key(1);
      String value = key.toString();
      assertSame(value, cache.getUnchecked(key));
      assertTrue(cache.asMap().containsKey(key));

But still, it is very powerful, and allows you to declare arbitrarily deeply nested dependency "graphs" (trees).

/// tip

All this might not seem as useful with these simple examples.

But you will see how useful it is in the chapters about **security**.

And you will also see the amounts of code it will save you.

 * part of the open-source <a href="https://github.com/google/guava">Guava</a> library.
 *
 * <p>The classes in this package include:
 *
 * <h2>Immutable collections</h2>
 *
 * These are collections whose contents will never change. They also offer a few additional
 * guarantees (see {@link ImmutableCollection} for details). Implementations are available for both

    public Slf4jStdoutLogger() {
        this(System.out);
    }

    public Slf4jStdoutLogger(PrintStream out) {
        this.out = requireNonNull(out);
    }

    //
    // These are the only methods we need in our primordial logger
    //
    public void error(String msg) {
        out.print(ERROR);
        out.println(msg);
    }

    public void error(String msg, Throwable t) {

		// extract the first, which should be the client IP.
		if match := forRegex.FindStringSubmatch(fwd); len(match) > 1 {
			// IPv6 addresses in Forwarded headers are quoted-strings. We strip
			// these quotes.
			addr = strings.Trim(match[1], `"`)
		}
	}

	return addr
}

// GetSourceIPRaw retrieves the IP from the request headers
// and falls back to r.RemoteAddr when necessary.

   * interpretation of a limited number of contiguously following characters.
   *
   * @since 8.0
   */
  public static final byte ESC = 27;

  /**
   * File Separator: These four information separators may be used within data in optional fashion,
   * except that their hierarchical relationship shall be: FS is the most inclusive, then GS, then

 * element. There are five new bulk-modification operations, for example {@link #add(Object, int)},
 * to add or remove multiple occurrences of an element at once, or to set the count of an element to
 * a specific value. These modification operations are optional, but implementations which support
 * the standard collection operations {@link #add(Object)} or {@link #remove(Object)} are encouraged