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/*
* Copyright 2015 the original author or 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 ratpack.health;
import ratpack.api.Nullable;
import ratpack.exec.Promise;
import ratpack.func.Function;
import ratpack.registry.Registry;
/**
* Reports on the health of some aspect of the system.
*
* Health checks are typically used for reporting and monitoring purposes.
* The results exposed by health checks can be reported via HTTP by a {@link ratpack.health.HealthCheckHandler}.
*
* The actual check is implemented by the {@link #check(Registry)} method, that returns a promise for a {@link Result}.
*
* The inspiration for health checks in Ratpack comes from the Dropwizard Metrics library.
* Ratpack health checks are different in that they support non blocking checks, and all health checks require a unique name.
*
* @see ratpack.health.HealthCheckHandler
*/
public interface HealthCheck {
/**
* The result of a health check.
*
* Instances can be created by one of the static methods of this class (e.g. {@link #healthy()}).
*/
class Result {
private static final Result HEALTHY = new Result(true, null, null);
private final boolean healthy;
private final String message;
private final Throwable error;
private Result(boolean healthy, String message, Throwable error) {
this.healthy = healthy;
this.message = message;
this.error = error;
}
/**
* Was the component being checked healthy?
*
* @return {@code true} if application component is healthy
*/
public boolean isHealthy() {
return healthy;
}
/**
* Any message provided as part of the check, may be {@code null}.
*
* A message may be provided with a healthy or unhealthy result.
*
* If {@link #getError()} is non null, this message will be the message provided by that exception.
*
* @return any message provided as part of the check, may be {@code null}
*/
@Nullable
public String getMessage() {
return message;
}
/**
* The exception representing an unhealthy check, may be {@code null}.
*
* Healthy results will never have an associated error.
*
* @return the exception representing an unhealthy check, may be {@code null}
*/
@Nullable
public Throwable getError() {
return error;
}
/**
* Creates a healthy result, with no message.
*
* @return a healthy result, with no message.
*/
public static Result healthy() {
return HEALTHY;
}
/**
* Creates a healthy result, with the given message.
*
* @param message a message to accompany the result
* @return a healthy result, with the given message
*/
public static Result healthy(String message) {
return new Result(true, message, null);
}
/**
* Creates a healthy result, with the given message.
*
* The message is constructed by {@link String#format(String, Object...)} and the given arguments.
*
* @param message the message format strings
* @param args values to be interpolated into the format string
* @return a healthy result, with the given message
*/
public static Result healthy(String message, Object... args) {
return healthy(String.format(message, args));
}
/**
* Creates an unhealthy result, with the given message.
*
* @param message a message to accompany the result
* @return an unhealthy result, with the given message
*/
public static Result unhealthy(String message) {
return new Result(false, message, null);
}
/**
* Creates an unhealthy result, with the given message.
*
* The message is constructed by {@link String#format(String, Object...)} and the given arguments.
*
* @param message the message format strings
* @param args values to be interpolated into the format string
* @return an unhealthy result, with the given message
*/
public static Result unhealthy(String message, Object... args) {
return unhealthy(String.format(message, args));
}
/**
* Creates an unhealthy result, with the given exception.
*
* The message of the given exception will also be used as the message of the result.
*
* @param error an exception thrown during health check
* @return an unhealthy result, with the given error
*/
public static Result unhealthy(Throwable error) {
return unhealthy(error.getMessage(), error);
}
/**
* Creates an unhealthy result, with the given exception and message.
*
* The supplied message will be used as the message of the result.
*
* @param message a message to accompany the result
* @param error an exception thrown during health check
* @return an unhealthy result, with the given error and message
* @since 1.2
*/
public static Result unhealthy(String message, Throwable error) {
return new Result(false, message, error);
}
}
/**
* The unique name of the health check.
*
* Each health check within an application must have a unique name.
*
* @return the name of the health check
*/
String getName();
/**
* Checks the health of the component, providing a promise for the result.
*
* This method returns a promise to allow check implementations to be asynchronous.
* If the implementation does not need to be asynchronous, the result can be returned via {@link Promise#value(Object)}.
*
* The {@code registry} argument is the server registry, from which other supporting objects can be obtained.
*
* If this method throws an exception, it is logically equivalent to returned an unhealthy result with the thrown exception.
*
* If the method returns a failed promise, it will be converted to a result using {@link Result#unhealthy(Throwable)}.
*
* @param registry the server registry
* @return a promise for the result
* @throws Exception any
*/
Promise check(Registry registry) throws Exception;
/**
* Convenience factory for health check implementations.
* {@code
* import ratpack.test.exec.ExecHarness;
* import ratpack.exec.Promise;
* import ratpack.registry.Registry;
* import ratpack.health.HealthCheck;
* import static org.junit.Assert.*;
*
* public class Example {
* public static void main(String... args) throws Exception {
* HealthCheck.Result result = ExecHarness.yieldSingle(e ->
* HealthCheck.of("test", registry ->
* Promise.value(HealthCheck.Result.healthy())
* ).check(Registry.empty())
* ).getValue();
*
* assertTrue(result.isHealthy());
* }
* }
* }
*
* @param name a name of health check
* @param func a health check implementation
* @return a named health check implementation
*/
static HealthCheck of(String name, Function> func) {
return new HealthCheck() {
@Override
public String getName() {
return name;
}
@Override
public Promise check(Registry registry) throws Exception {
return func.apply(registry);
}
};
}
}