For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

## Use cases { #use-cases }

Some use cases include:

            }

            startLatch.countDown();
            executor.shutdown();
            assertTrue(executor.awaitTermination(5, TimeUnit.SECONDS));

            // Some operations might succeed before key wipe, some might fail after
            // At minimum, we expect some activity (not all operations should be no-ops)
            int totalOperations = successCount.get() + failureCount.get();

 * prefer the simplest interface that satisfies your use case. See the <a
 * href="https://github.com/google/guava/wiki/GraphsExplained#choosing-the-right-graph-type">
 * "Choosing the right graph type"</a> section of the Guava User Guide for more details.
 *
 * <h3>Capabilities</h3>
 *
 * <p>{@code Graph} supports the following use cases (<a

 * prefer the simplest interface that satisfies your use case. See the <a
 * href="https://github.com/google/guava/wiki/GraphsExplained#choosing-the-right-graph-type">
 * "Choosing the right graph type"</a> section of the Guava User Guide for more details.
 *
 * <h3>Capabilities</h3>
 *
 * <p>{@code Graph} supports the following use cases (<a

    builder.put("d", 2);
    builder.put("a", 5);
    builder.orderKeysBy(
        new Ordering<String>() {
          @Override
          public int compare(String left, String right) {
            return left.length() - right.length();
          }
        });
    builder.put("cc", 4);
    builder.put("a", 2);
    builder.put("bb", 6);
    ImmutableListMultimap<String, Integer> multimap = builder.build();

 *
 * <p>A non-null {@code Optional<T>} reference can be used as a replacement for a nullable {@code T}
 * reference. It allows you to represent "a {@code T} that must be present" and a "a {@code T} that
 * might be absent" as two distinct types in your program, which can aid clarity.
 *
 * <p>Some uses of this class include
 *
 * <ul>
 *   <li>As a method return type, as an alternative to returning {@code null} to indicate that no

public final class ArbitraryInstances {

  private static final Ordering<Field> BY_FIELD_NAME =
      new Ordering<Field>() {
        @Override
        public int compare(Field left, Field right) {
          return left.getName().compareTo(right.getName());
        }
      };

  /**
   * Returns a new {@code MatchResult} that corresponds to a successful match. Apache Harmony (used

            parameterOffset += pad;

            totalParameterCount = writeParametersWireFormat(txn_buf, bufParameterOffset);
            bufDataOffset = totalParameterCount; // data comes right after data

            int available = maxBufferSize - parameterOffset;
            parameterCount = Math.min(totalParameterCount, available);
            available -= parameterCount;

# Migrate from Pydantic v1 to Pydantic v2 { #migrate-from-pydantic-v1-to-pydantic-v2 }

If you have an old FastAPI app, you might be using Pydantic version 1.

FastAPI version 0.100.0 had support for either Pydantic v1 or v2. It would use whichever you had installed.

FastAPI version 0.119.0 introduced partial support for Pydantic v1 from inside of Pydantic v2 (as `pydantic.v1`), to facilitate the migration to v2.

            }
            buffer.append(proxy.getHost()).append(':').append(proxy.getPort()).append('>');
        }

        // consider the username&password because a repo manager might block artifacts depending on authorization
        Authentication auth = repository.getAuthentication();
        if (auth != null) {
            int hash = (auth.getUsername() + auth.getPassword()).hashCode();