Component.java

/**
 * Copyright 2015-2017 The OpenZipkin Authors
 *
 * Licensed 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://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.
 */
package zipkin2;

import java.io.Closeable;
import java.io.IOException;

/**
 * Components are object graphs used to compose a zipkin service or client. For example, a storage
 * component might return a query api.
 *
 * <p>Components are lazy with regards to I/O. They can be injected directly to other components so
 * as to avoid crashing the application graph if a network service is unavailable.
 */
public abstract class Component implements Closeable {

  /**
   * Answers the question: Are operations on this component likely to succeed?
   *
   * <p>Implementations should initialize the component if necessary. It should test a remote
   * connection, or consult a trusted source to derive the result. They should use least resources
   * possible to establish a meaningful result, and be safe to call many times, even concurrently.
   *
   * @see CheckResult#OK
   */
  public CheckResult check() {
    return CheckResult.OK;
  }

  /**
   * Closes any network resources created implicitly by the component.
   *
   * <p>For example, if this created a connection, it would close it. If it was provided one, this
   * would close any sessions, but leave the connection open.
   */
  @Override public void close() throws IOException {
  }
}