The user of your API (an external developer) will create an invoice in your API with a POST request.

Then your API will (let's imagine):

* Send the invoice to some customer of the external developer.
* Collect the money.
* Send a notification back to the API user (the external developer).
    * This will be done by sending a POST request (from *your API*) to some *external API* provided by that external developer (this is the "callback").

                .filter(StringUtil::isNotBlank)
                .distinct()
                .collect(Collectors.joining("\n")));
        body.virtualHosts = stream(entity.getVirtualHosts())
                .get(stream -> stream.filter(StringUtil::isNotBlank).distinct().map(String::trim).collect(Collectors.joining("\n")));
        return body;
    }

 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect.testing;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;

 * express or implied. See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.collect.Hashing.smear;

import com.google.common.annotations.GwtCompatible;
import junit.framework.TestCase;
import org.jspecify.annotations.NullMarked;

/** Tests for {@code Hashing}. */

 * limitations under the License.
 */

package com.google.common.util.concurrent;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.common.collect.ForwardingDeque;
import java.util.Collection;
import java.util.concurrent.BlockingDeque;
import java.util.concurrent.TimeUnit;
import org.jspecify.annotations.Nullable;

/**

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect.testing.testers;

import static com.google.common.collect.testing.Helpers.getMethod;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;

 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.collect.Tables.immutableCell;
import static com.google.common.truth.Truth.assertThat;

import com.google.common.annotations.GwtCompatible;
import com.google.common.collect.Table.Cell;
import org.jspecify.annotations.NullMarked;

/**
 * @author Gregory Kick
 */
@GwtCompatible

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.collect.Iterables.getOnlyElement;
import static com.google.common.collect.Iterables.unmodifiableIterable;
import static com.google.common.reflect.Reflection.newProxy;
import static java.util.Arrays.asList;

import com.google.common.base.Function;
import com.google.common.cache.CacheBuilderFactory.DurationSpec;
import com.google.common.cache.LocalCache.Strength;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Iterables;
import com.google.common.collect.Maps;
import com.google.common.testing.EqualsTester;
import java.util.Collection;
import java.util.Map.Entry;
import java.util.Set;

            servletContext.setSessionTrackingModes(
                    fessConfig.getSessionTrackingModesAsSet().stream().map(SessionTrackingMode::valueOf).collect(Collectors.toSet()));
        } catch (final Throwable t) {
            logger.warn("Failed to set SessionTrackingMode.", t);
        }