juneau-rest/juneau-rest-server/src/main/java/org/apache/juneau/rest/RestServlet.java

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package org.apache.juneau.rest;

import static java.util.logging.Level.*;
import static javax.servlet.http.HttpServletResponse.*;
import static org.apache.juneau.internal.StringUtils.*;
import static org.apache.juneau.rest.HttpRuntimeException.*;
import static org.apache.juneau.rest.annotation.HookEvent.*;

import java.io.*;
import java.lang.reflect.Method;
import java.text.*;
import java.util.*;
import java.util.function.*;
import java.util.logging.*;

import javax.servlet.*;
import javax.servlet.http.*;

import org.apache.juneau.internal.*;
import org.apache.juneau.reflect.*;
import org.apache.juneau.rest.annotation.*;
import org.apache.juneau.cp.*;
import org.apache.juneau.dto.swagger.*;
import org.apache.juneau.http.exception.*;

/**
 * Servlet implementation of a REST resource.
 *
 * <ul class='seealso'>
 * 	<li class='link'>{@doc juneau-rest-server.Instantiation.RestServlet}
 * </ul>
 */
public abstract class RestServlet extends HttpServlet implements RestInfoProvider, RestCallLogger, RestResourceResolver, ResourceFinder {

	private static final long serialVersionUID = 1L;

	private RestContextBuilder builder;
	private volatile RestContext context;
	private volatile Exception initException;
	private boolean isInitialized = false;  // Should not be volatile.
	private volatile RestResourceResolver resourceResolver = new BasicRestResourceResolver();
	private Logger logger = Logger.getLogger(getClass().getName());
	private RestInfoProvider infoProvider;
	private RestCallLogger callLogger;
	private ResourceFinder resourceFinder;

	@Override /* Servlet */
	public final synchronized void init(ServletConfig servletConfig) throws ServletException {
		try {
			if (context != null)
				return;
			builder = RestContext.create(servletConfig, this.getClass(), null);
			if (resourceResolver != null)
				builder.resourceResolver(resourceResolver);
			builder.init(this);
			super.init(servletConfig);
			builder.servletContext(this.getServletContext());
			setContext(builder.build());
			context.postInitChildFirst();
		} catch (ServletException e) {
			initException = e;
			log(SEVERE, e, "Servlet init error on class ''{0}''", getClass().getName());
			throw e;
		} catch (Throwable e) {
			initException = toHttpException(e, InternalServerError.class);
			log(SEVERE, e, "Servlet init error on class ''{0}''", getClass().getName());
		}
	}

	/*
	 * Bypasses the init(ServletConfig) method and just calls the super.init(ServletConfig) method directly.
	 * Used when subclasses of RestServlet are attached as child resources.
	 */
	synchronized void innerInit(ServletConfig servletConfig) throws ServletException {
		super.init(servletConfig);
	}

	/**
	 * Sets the context object for this servlet.
	 *
	 * @param context Sets the context object on this servlet.
	 * @throws ServletException If error occurred during post-initialiation.
	 */
	public synchronized void setContext(RestContext context) throws ServletException {
		this.builder = context.builder;
		this.context = context;
		isInitialized = true;
		infoProvider = new BasicRestInfoProvider(context);
		callLogger = new BasicRestCallLogger(context);
		resourceFinder = new RecursiveResourceFinder();
		context.postInit();
	}

	/**
	 * Returns <jk>true</jk> if this servlet has been initialized and {@link #getContext()} returns a value.
	 *
	 * @return <jk>true</jk> if this servlet has been initialized and {@link #getContext()} returns a value.
	 */
	public synchronized boolean isInitialized() {
		return isInitialized;
	}

	/**
	 * Sets the resource resolver to use for this servlet and all child servlets.
	 * <p>
	 * This method can be called immediately following object construction, but must be called before {@link #init(ServletConfig)} is called.
	 * Otherwise calling this method will have no effect.
	 *
	 * @param resourceResolver The resolver instance.  Can be <jk>null</jk>.
	 * @return This object (for method chaining).
	 */
	public synchronized RestServlet setRestResourceResolver(RestResourceResolver resourceResolver) {
		this.resourceResolver = resourceResolver;
		return this;
	}

	/**
	 * Returns the path defined on this servlet if it's defined via {@link Rest#path()}.
	 *
	 * @return The path defined on this servlet, or an empty string if not specified.
	 */
	@SuppressWarnings("deprecation")
	public synchronized String getPath() {
		if (context != null)
			return context.getPath();
		ClassInfo ci = ClassInfo.of(getClass());
		String path = "";
		for (Rest rr : ci.getAnnotations(Rest.class))
			if (! rr.path().isEmpty())
				path = trimSlashes(rr.path());
		if (! path.isEmpty())
			return path;
		for (RestResource rr : ci.getAnnotations(RestResource.class))
			if (! rr.path().isEmpty())
				path = trimSlashes(rr.path());
		return "";
	}

	@Override /* GenericServlet */
	public synchronized RestContextBuilder getServletConfig() {
		return builder;
	}

	//-----------------------------------------------------------------------------------------------------------------
	// Context methods.
	//-----------------------------------------------------------------------------------------------------------------

	/**
	 * Returns the read-only context object that contains all the configuration information about this resource.
	 *
	 * <p>
	 * This object is <jk>null</jk> during the call to {@link #init(ServletConfig)} but is populated by the time
	 * {@link #init()} is called.
	 *
	 * <p>
	 * Resource classes that don't extend from {@link RestServlet} can add the following method to their class to get
	 * access to this context object:
	 * <p class='bcode w800'>
	 * 	<jk>public void</jk> init(RestServletContext context) <jk>throws</jk> Exception;
	 * </p>
	 *
	 * @return The context information on this servlet.
	 */
	public synchronized RestContext getContext() {
		if (context == null)
			throw new InternalServerError("RestContext object not set on resource.");
		return context;
	}

	/**
	 * Convenience method for calling <c>getContext().getProperties();</c>
	 *
	 * @return The resource properties as an {@link RestContextProperties}.
	 * @see RestContext#getProperties()
	 */
	public RestContextProperties getProperties() {
		return getContext().getProperties();
	}


	//-----------------------------------------------------------------------------------------------------------------
	// Convenience logger methods
	//-----------------------------------------------------------------------------------------------------------------

	/**
	 * Log a message at {@link Level#INFO} level.
	 *
	 * <p>
	 * Subclasses can intercept the handling of these messages by overriding {@link #doLog(Level, Throwable, Supplier)}.
	 *
	 * @param msg The message to log.
	 */
	@Override /* GenericServlet */
	public void log(String msg) {
		doLog(Level.INFO, null, () -> msg);
	}

	/**
	 * Log a message.
	 *
	 * <p>
	 * Subclasses can intercept the handling of these messages by overriding {@link #doLog(Level, Throwable, Supplier)}.
	 *
	 * @param msg The message to log.
	 * @param cause The cause.
	 */
	@Override /* GenericServlet */
	public void log(String msg, Throwable cause) {
		doLog(Level.INFO, null, () -> msg);
	}

	/**
	 * Log a message.
	 *
	 * <p>
	 * Subclasses can intercept the handling of these messages by overriding {@link #doLog(Level, Throwable, Supplier)}.
	 *
	 * @param level The log level.
	 * @param msg The message to log.
	 * @param args Optional {@link MessageFormat}-style arguments.
	 */
	public void log(Level level, String msg, Object...args) {
		doLog(level, null, () -> StringUtils.format(msg, args));
	}

	/**
	 * Log a message.
	 *
	 * <p>
	 * Subclasses can intercept the handling of these messages by overriding {@link #doLog(Level, Throwable, Supplier)}.
	 *
	 * @param level The log level.
	 * @param cause The cause.
	 * @param msg The message to log.
	 * @param args Optional {@link MessageFormat}-style arguments.
	 */
	public void log(Level level, Throwable cause, String msg, Object...args) {
		doLog(level, cause, () -> StringUtils.format(msg, args));
	}

	/**
	 * Main logger method.
	 *
	 * <p>
	 * The default behavior logs a message to the Java logger of the class name.
	 *
	 * <p>
	 * Subclasses can override this method to implement their own logger handling.
	 *
	 * @param level The log level.
	 * @param cause Optional throwable.
	 * @param msg The message to log.
	 */
	protected void doLog(Level level, Throwable cause, Supplier<String> msg) {
		logger.log(level, cause, msg);
	}

	//-----------------------------------------------------------------------------------------------------------------
	// Lifecycle methods
	//-----------------------------------------------------------------------------------------------------------------

	/**
	 * The main service method.
	 *
	 * <p>
	 * Subclasses can optionally override this method if they want to tailor the behavior of requests.
	 */
	@Override /* Servlet */
	public void service(HttpServletRequest r1, HttpServletResponse r2) throws ServletException, InternalServerError, IOException {
		try {
			// To avoid checking the volatile field context on every call, use the non-volatile isInitialized field as a first-check check.
			if (! isInitialized) {
				if (initException != null)
					throw initException;
				if (context == null)
					throw new InternalServerError("Servlet {0} not initialized.  init(ServletConfig) was not called.  This can occur if you've overridden this method but didn't call super.init(RestConfig).", getClass().getName());
				isInitialized = true;
			}

			context.execute(r1, r2);

		} catch (Throwable e) {
			r2.sendError(SC_INTERNAL_SERVER_ERROR, e.getLocalizedMessage());
		}
	}

	@Override /* GenericServlet */
	public synchronized void destroy() {
		if (context != null)
			context.destroy();
		super.destroy();
	}

	//-----------------------------------------------------------------------------------------------------------------
	// Hook events
	//-----------------------------------------------------------------------------------------------------------------

	/**
	 * Method that gets called during servlet initialization.
	 *
	 * <p>
	 * This method is called from within the {@link Servlet#init(ServletConfig)} method after the {@link RestContextBuilder}
	 * object has been created and initialized with the annotations defined on the class, but before the
	 * {@link RestContext} object has been created.
	 *
	 * <p>
	 * An example of this is the <c>PetStoreResource</c> class that uses an init method to perform initialization
	 * of an internal data structure.
	 *
	 * <h5 class='figure'>Example:</h5>
	 * <p class='bcode w800'>
	 * 	<ja>@Rest</ja>(...)
	 * 	<jk>public class</jk> PetStoreResource <jk>extends</jk> ResourceJena {
	 *
	 * 		<jc>// Our database.</jc>
	 * 		<jk>private</jk> Map&lt;Integer,Pet&gt; <jf>petDB</jf>;
	 *
	 * 		<ja>@Override</ja>
	 * 		<jk>public void</jk> onInit(RestContextBuilder builder) <jk>throws</jk> Exception {
	 * 			<jc>// Load our database from a local JSON file.</jc>
	 * 			<jf>petDB</jf> = JsonParser.<jsf>DEFAULT</jsf>.parse(getClass().getResourceAsStream(<js>"PetStore.json"</js>), LinkedHashMap.<jk>class</jk>, Integer.<jk>class</jk>, Pet.<jk>class</jk>);
	 * 		}
	 * 	}
	 * </p>
	 *
	 * <ul class='notes'>
	 * 	<li>
	 * 		The default implementation of this method is a no-op.
	 * 	<li>
	 * 		Multiple INIT methods can be defined on a class.
	 * 		<br>INIT methods on parent classes are invoked before INIT methods on child classes.
	 * 		<br>The order of INIT method invocations within a class is alphabetical, then by parameter count, then by parameter types.
	 * 	<li>
	 * 		The method can throw any exception causing initialization of the servlet to fail.
	 * </ul>
	 *
	 * @param builder Context builder which can be used to configure the servlet.
	 * @throws Exception Any exception thrown will cause servlet to fail startup.
	 */
	@RestHook(INIT)
	public void onInit(RestContextBuilder builder) throws Exception {}

	/**
	 * Method that gets called immediately after servlet initialization.
	 *
	 * <p>
	 * This method is called from within the {@link Servlet#init(ServletConfig)} method after the {@link RestContext}
	 * object has been created.
	 *
	 * <ul class='notes'>
	 * 	<li>
	 * 		The default implementation of this method is a no-op.
	 * 	<li>
	 * 		Multiple POST_INIT methods can be defined on a class.
	 * 		<br>POST_INIT methods on parent classes are invoked before POST_INIT methods on child classes.
	 * 		<br>The order of POST_INIT method invocations within a class is alphabetical, then by parameter count, then by parameter types.
	 * 	<li>
	 * 		The method can throw any exception causing initialization of the servlet to fail.
	 * </ul>
	 *
	 * @param context The initialized context object.
	 * @throws Exception Any exception thrown will cause servlet to fail startup.
	 */
	@RestHook(POST_INIT)
	public void onPostInit(RestContext context) throws Exception {}

	/**
	 * Identical to {@link #onPostInit(RestContext)} except the order of execution is child-resources first.
	 *
	 * <p>
	 * Use this method if you need to perform any kind of initialization on child resources before the parent resource.
	 *
	 * <p>
	 * This method is called from within the {@link Servlet#init(ServletConfig)} method after the {@link RestContext}
	 * object has been created and after the {@link HookEvent#POST_INIT} methods have been called.
	 *
	 * <p>
	 * The only valid parameter type for this method is {@link RestContext} which can be used to retrieve information
	 * about the servlet.
	 *
	 * <ul class='notes'>
	 * 	<li>
	 * 		The default implementation of this method is a no-op.
	 * 	<li>
	 * 		Multiple POST_INIT_CHILD_FIRST methods can be defined on a class.
	 * 		<br>POST_INIT_CHILD_FIRST methods on parent classes are invoked before POST_INIT_CHILD_FIRST methods on child classes.
	 * 		<br>The order of POST_INIT_CHILD_FIRST method invocations within a class is alphabetical, then by parameter count, then by parameter types.
	 * 	<li>
	 * 		The method can throw any exception causing initialization of the servlet to fail.
	 * </ul>
	 *
	 * @param context The initialized context object.
	 * @throws Exception Any exception thrown will cause servlet to fail startup.
	 */
	@RestHook(POST_INIT_CHILD_FIRST)
	public void onPostInitChildFirst(RestContext context) throws Exception {}

	/**
	 * Method that gets called during servlet destroy.
	 *
	 * <p>
	 * This method is called from within the {@link Servlet#destroy()}.
	 *
	 * <h5 class='figure'>Example:</h5>
	 * <p class='bcode w800'>
	 * 	<ja>@Rest</ja>(...)
	 * 	<jk>public class</jk> PetStoreResource <jk>extends</jk> ResourceJena {
	 *
	 * 		<jc>// Our database.</jc>
	 * 		<jk>private</jk> Map&lt;Integer,Pet&gt; <jf>petDB</jf>;
	 *
	 * 		<ja>@Override</ja>
	 * 		<jk>public void</jk> onDestroy(RestContext context) {
	 * 			<jf>petDB</jf> = <jk>null</jk>;
	 * 		}
	 * 	}
	 * </p>
	 *
	 * <ul class='notes'>
	 * 	<li>
	 * 		The default implementation of this method is a no-op.
	 * 	<li>
	 * 		Multiple DESTROY methods can be defined on a class.
	 * 		<br>DESTROY methods on child classes are invoked before DESTROY methods on parent classes.
	 * 		<br>The order of DESTROY method invocations within a class is alphabetical, then by parameter count, then by parameter types.
	 * 	<li>
	 * 		In general, destroy methods should not throw any exceptions, although if any are thrown, the stack trace will be
	 * 		printed to <c>System.err</c>.
	 * </ul>
	 *
	 * @param context The initialized context object.
	 * @throws Exception Any exception thrown will cause stack trace to be printed to <c>System.err</c>.
	 */
	@RestHook(DESTROY)
	public void onDestroy(RestContext context) throws Exception {}

	/**
	 * A method that is called immediately after the <c>HttpServlet.service(HttpServletRequest, HttpServletResponse)</c>
	 * method is called.
	 *
	 * <p>
	 * Note that you only have access to the raw request and response objects at this point.
	 *
	 * <h5 class='figure'>Example:</h5>
	 * <p class='bcode w800'>
	 * 	<ja>@Rest</ja>(...)
	 * 	<jk>public class</jk> MyResource <jk>extends</jk> BasicRestServlet {
	 *
	 * 		<jc>// Add a request attribute to all incoming requests.</jc>
	 * 		<ja>@Override</ja>
	 * 		<jk>public void</jk> onStartCall(HttpServletRequest req, HttpServletResponse res) {
	 * 			req.setAttribute(<js>"foobar"</js>, <jk>new</jk> FooBar());
	 * 		}
	 * 	}
	 * </p>
	 *
	 * <ul class='notes'>
	 * 	<li>
	 * 		The default implementation of this method is a no-op.
	 * 	<li>
	 * 		Multiple START_CALL methods can be defined on a class.
	 * 		<br>START_CALL methods on parent classes are invoked before START_CALL methods on child classes.
	 * 		<br>The order of START_CALL method invocations within a class is alphabetical, then by parameter count, then by parameter types.
	 * 	<li>
	 * 		The method can throw any exception.
	 * 		<br>{@link HttpException HttpExceptions} can be thrown to cause a particular HTTP error status code.
	 * 		<br>All other exceptions cause an HTTP 500 error status code.
	 * </ul>
	 *
	 * @param req The HTTP servlet request object.
	 * @param res The HTTP servlet response object.
	 * @throws Exception Any exception.
	 */
	@RestHook(START_CALL)
	public void onStartCall(HttpServletRequest req, HttpServletResponse res) throws Exception {}

	/**
	 * Method that gets called immediately before the <ja>@RestMethod</ja> annotated method gets called.
	 *
	 * <p>
	 * At this point, the {@link RestRequest} object has been fully initialized, and all {@link RestGuard} and
	 * {@link RestMatcher} objects have been called.
	 *
	 * <ul class='notes'>
	 * 	<li>
	 * 		The default implementation of this method is a no-op.
	 * 	<li>
	 * 		Multiple PRE_CALL methods can be defined on a class.
	 * 		<br>PRE_CALL methods on parent classes are invoked before PRE_CALL methods on child classes.
	 * 		<br>The order of PRE_CALL method invocations within a class is alphabetical, then by parameter count, then by parameter types.
	 * 	<li>
	 * 		The method can throw any exception.
	 * 		<br>{@link HttpException HttpExceptions} can be thrown to cause a particular HTTP error status code.
	 * 		<br>All other exceptions cause an HTTP 500 error status code.
	 * 	<li>
	 * 		It's advisable not to mess around with the HTTP body itself since you may end up consuming the body
	 * 		before the actual REST method has a chance to use it.
	 * </ul>
	 *
	 * @param req The request object.
	 * @param res The response object.
	 * @throws Exception Any exception.
	 */
	@RestHook(PRE_CALL)
	public void onPreCall(RestRequest req, RestResponse res) throws Exception {}

	/**
	 * Method that gets called immediately after the <ja>@RestMethod</ja> annotated method gets called.
	 *
	 * <p>
	 * At this point, the output object returned by the method call has been set on the response, but
	 * {@link RestConverter RestConverters} have not yet been executed and the response has not yet been written.
	 *
	 * <ul class='notes'>
	 * 	<li>
	 * 		The default implementation of this method is a no-op.
	 * 	<li>
	 * 		Multiple POST_CALL methods can be defined on a class.
	 * 		<br>POST_CALL methods on parent classes are invoked before POST_CALL methods on child classes.
	 * 		<br>The order of POST_CALL method invocations within a class is alphabetical, then by parameter count, then by parameter types.
	 * 	<li>
	 * 		The method can throw any exception, although at this point it is too late to set an HTTP error status code.
	 * </ul>
	 *
	 * @param req The request object.
	 * @param res The response object.
	 * @throws Exception Any exception.
	 */
	@RestHook(POST_CALL)
	public void onPostCall(RestRequest req, RestResponse res) throws Exception {}

	/**
	 * Method that gets called right before we exit the servlet service method.
	 *
	 * <p>
	 * At this point, the output has been written and flushed.
	 *
	 * <p>
	 * The following attributes are set on the {@link HttpServletRequest} object that can be useful for logging purposes:
	 * <ul>
	 * 	<li><js>"Exception"</js> - Any exceptions thrown during the request.
	 * 	<li><js>"ExecTime"</js> - Execution time of the request.
	 * </ul>
	 *
	 * <ul class='notes'>
	 * 	<li>
	 * 		The default implementation of this method is a no-op.
	 * 	<li>
	 * 		Multiple END_CALL methods can be defined on a class.
	 * 		<br>END_CALL methods on parent classes are invoked before END_CALL methods on child classes.
	 * 		<br>The order of END_CALL method invocations within a class is alphabetical, then by parameter count, then by parameter types.
	 * 	<li>
	 * 		The method can throw any exception, although at this point it is too late to set an HTTP error status code.
	 * 	<li>
	 * 		Note that if you override a parent method, you probably need to call <code><jk>super</jk>.parentMethod(...)</code>.
	 * 		<br>The method is still considered part of the parent class for ordering purposes even though it's
	 * 		overridden by the child class.
	 * </ul>
	 *
	 * @param req The HTTP servlet request object.
	 * @param res The HTTP servlet response object.
	 * @throws Exception Any exception.
	 */
	@RestHook(END_CALL)
	public void onEndCall(HttpServletRequest req, HttpServletResponse res) throws Exception {}

	//-----------------------------------------------------------------------------------------------------------------
	// Other methods.
	//-----------------------------------------------------------------------------------------------------------------

	/**
	 * Returns the current HTTP request.
	 *
	 * @return The current HTTP request, or <jk>null</jk> if it wasn't created.
	 */
	public synchronized RestRequest getRequest() {
		return getContext().getRequest();
	}

	/**
	 * Returns the current HTTP response.
	 *
	 * @return The current HTTP response, or <jk>null</jk> if it wasn't created.
	 */
	public synchronized RestResponse getResponse() {
		return getContext().getResponse();
	}


	//-----------------------------------------------------------------------------------------------------------------
	// RestInfoProvider
	//-----------------------------------------------------------------------------------------------------------------

	@Override /* RestInfoProvider */
	public Swagger getSwagger(RestRequest req) throws Exception {
		return infoProvider.getSwagger(req);
	}

	@Override /* RestInfoProvider */
	public String getSiteName(RestRequest req) throws Exception {
		return infoProvider.getSiteName(req);
	}

	@Override /* RestInfoProvider */
	public String getTitle(RestRequest req) throws Exception {
		return infoProvider.getTitle(req);
	}

	@Override /* RestInfoProvider */
	public String getDescription(RestRequest req) throws Exception {
		return infoProvider.getDescription(req);
	}

	@Override /* RestInfoProvider */
	public String getMethodSummary(Method method, RestRequest req) throws Exception {
		return infoProvider.getMethodSummary(method, req);
	}

	@Override /* RestInfoProvider */
	public String getMethodDescription(Method method, RestRequest req) throws Exception {
		return infoProvider.getMethodDescription(method, req);
	}

	//-----------------------------------------------------------------------------------------------------------------
	// RestCallLogger
	//-----------------------------------------------------------------------------------------------------------------

	@Override /* RestCallLogger */
	public void log(RestCallLoggerConfig config, HttpServletRequest req, HttpServletResponse res) {
		callLogger.log(config, req, res);
	}

	//-----------------------------------------------------------------------------------------------------------------
	// ClasspathResourceFinder
	//-----------------------------------------------------------------------------------------------------------------

	@Override /* ClasspathResourceFinder */
	public InputStream findResource(Class<?> baseClass, String name, Locale locale) throws IOException {
		return resourceFinder.findResource(baseClass, name, locale);
	}

	//-----------------------------------------------------------------------------------------------------------------
	// RestResourceResolver
	//-----------------------------------------------------------------------------------------------------------------

	@Override /* RestResourceResolver */
	public <T> T resolve(Object parent, Class<T> c, Object... args) {
		return resourceResolver.resolve(parent, c, args);
	}

	@Override /* RestResourceResolver */
	public <T> T resolve(Object parent, Class<T> c, RestContextBuilder builder, Object... args) throws Exception {
		return resourceResolver.resolve(parent, c, builder, args);
	}
}