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package com.yammer.metrics.core;
/**
* A health check for a component of your application.
*/
public abstract class HealthCheck {
/**
* The result of a {@link HealthCheck} being run. It can be healthy (with an optional message)
* or unhealthy (with either an error message or a thrown exception).
*/
public static class Result {
private static final Result HEALTHY = new Result(true, null, null);
private static final int PRIME = 31;
/**
* Returns a healthy {@link Result} with no additional message.
*
* @return a healthy {@link Result} with no additional message
*/
public static Result healthy() {
return HEALTHY;
}
/**
* Returns a healthy {@link Result} with an additional message.
*
* @param message an informative message
* @return a healthy {@link Result} with an additional message
*/
public static Result healthy(String message) {
return new Result(true, message, null);
}
/**
* Returns a healthy {@link Result} with a formatted message.
*
* Message formatting follows the same rules as
* {@link String#format(String, Object...)}.
*
* @param message a message format
* @param args the arguments apply to the message format
* @return a healthy {@link Result} with an additional message
* @see String#format(String, Object...)
*/
public static Result healthy(String message, Object... args) {
return healthy(String.format(message, args));
}
/**
* Returns an unhealthy {@link Result} with the given message.
*
* @param message an informative message describing how the health check failed
* @return an unhealthy {@link Result} with the given message
*/
public static Result unhealthy(String message) {
return new Result(false, message, null);
}
/**
* Returns an unhealthy {@link Result} with a formatted message.
*
* Message formatting follows the same rules as
* {@link String#format(String, Object...)}.
*
* @param message a message format
* @param args the arguments apply to the message format
* @return an unhealthy {@link Result} with an additional message
* @see String#format(String, Object...)
*/
public static Result unhealthy(String message, Object... args) {
return unhealthy(String.format(message, args));
}
/**
* Returns an unhealthy {@link Result} with the given error.
*
* @param error an exception thrown during the health check
* @return an unhealthy {@link Result} with the given error
*/
public static Result unhealthy(Throwable error) {
return new Result(false, error.getMessage(), error);
}
private final boolean healthy;
private final String message;
private final Throwable error;
private Result(boolean isHealthy, String message, Throwable error) {
this.healthy = isHealthy;
this.message = message;
this.error = error;
}
/**
* Returns {@code true} if the result indicates the component is healthy; {@code false}
* otherwise.
* @return {@code true} if the result indicates the component is healthy
*/
public boolean isHealthy() {
return healthy;
}
/**
* Returns any additional message for the result, or {@code null} if the result has no
* message.
*
* @return any additional message for the result, or {@code null}
*/
public String getMessage() {
return message;
}
/**
* Returns any exception for the result, or {@code null} if the result has no exception.
*
* @return any exception for the result, or {@code null}
*/
public Throwable getError() {
return error;
}
@Override
public boolean equals(Object o) {
if (this == o) { return true; }
if (o == null || getClass() != o.getClass()) { return false; }
final Result result = (Result) o;
return healthy == result.healthy &&
!(error != null ? !error.equals(result.error) : result.error != null) &&
!(message != null ? !message.equals(result.message) : result.message != null);
}
@Override
public int hashCode() {
int result = (healthy ? 1 : 0);
result = PRIME * result + (message != null ? message.hashCode() : 0);
result = PRIME * result + (error != null ? error.hashCode() : 0);
return result;
}
@Override
public String toString() {
final StringBuilder builder = new StringBuilder("Result{isHealthy=");
builder.append(healthy);
if (message != null) {
builder.append(", message=").append(message);
}
if (error != null) {
builder.append(", error=").append(error);
}
builder.append('}');
return builder.toString();
}
}
private final String name;
/**
* Create a new {@link HealthCheck} instance with the given name.
*
* @param name the name of the health check (and, ideally, the name of the underlying
* component the health check tests)
*/
protected HealthCheck(String name) {
this.name = name;
}
/**
* Returns the health check's name.
*
* @return the health check's name
*/
public String getName() {
return name;
}
/**
* Perform a check of the application component.
*
* @return if the component is healthy, a healthy {@link Result}; otherwise, an unhealthy
* {@link Result} with a descriptive error message or exception
*
* @throws Exception if there is an unhandled error during the health check; this will result in
* a failed health check
*/
protected abstract Result check() throws Exception;
/**
* Executes the health check, catching and handling any exceptions raised by {@link #check()}.
*
* @return if the component is healthy, a healthy {@link Result}; otherwise, an unhealthy
* {@link Result} with a descriptive error message or exception
*/
public Result execute() {
try {
return check();
} catch (Error e) {
throw e;
} catch (Throwable e) {
return Result.unhealthy(e);
}
}
}
