javax.websocket.OnMessage Maven / Gradle / Ivy
/*
* Copyright (c) 2018 Oracle and/or its affiliates and others.
* All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0, which is available at
* http://www.eclipse.org/legal/epl-2.0.
*
* This Source Code may also be made available under the following Secondary
* Licenses when the conditions for such availability set forth in the
* Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
* version 2 with the GNU Classpath Exception, which is available at
* https://www.gnu.org/software/classpath/license.html.
*
* SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
*/
package javax.websocket;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* This method level annotation can be used to make a Java method receive incoming web socket messages. Each websocket
* endpoint may only have one message handling method for each of the native websocket message formats: text, binary and
* pong. Methods using this annotation are allowed to have parameters of types described below, otherwise the container
* will generate an error at deployment time.
*
* The allowed parameters are:
*
* - Exactly one of any of the following choices
*
* - if the method is handling text messages:
*
* - {@link java.lang.String} to receive the whole message
* - Java primitive or class equivalent to receive the whole message converted to that type
* - String and boolean pair to receive the message in parts
* - {@link java.io.Reader} to receive the whole message as a blocking stream
* - any object parameter for which the endpoint has a text decoder ({@link Decoder.Text} or
* {@link Decoder.TextStream}).
*
*
* - if the method is handling binary messages:
*
* - byte[] or {@link java.nio.ByteBuffer} to receive the whole message
* - byte[] and boolean pair, or {@link java.nio.ByteBuffer} and boolean pair to receive the message in parts
* - {@link java.io.InputStream} to receive the whole message as a blocking stream
* - any object parameter for which the endpoint has a binary decoder ({@link Decoder.Binary} or
* {@link Decoder.BinaryStream}).
*
*
* - if the method is handling pong messages:
*
* - {@link PongMessage} for handling pong messages
*
*
*
*
* - and Zero to n String or Java primitive parameters annotated with the {@code javax.websocket.server.PathParam}
* annotation for server endpoints.
* - and an optional {@link Session} parameter
*
*
* The parameters may be listed in any order.
*
*
* The method may have a non-void return type, in which case the web socket runtime must interpret this as a web socket
* message to return to the peer. The allowed data types for this return type, other than void, are String, ByteBuffer,
* byte[], any Java primitive or class equivalent, and anything for which there is an encoder. If the method uses a Java
* primitive as a return value, the implementation must construct the text message to send using the standard Java
* string representation of the Java primitive unless there developer provided encoder for the type configured for this
* endpoint, in which case that encoder must be used. If the method uses a class equivalent of a Java primitive as a
* return value, the implementation must construct the text message from the Java primitive equivalent as described
* above.
*
*
* Developers should note that if developer closes the session during the invocation of a method with a return type, the
* method will complete but the return value will not be delivered to the remote endpoint. The send failure will be
* passed back into the endpoint's error handling method.
*
*
* For example:
*
*
*
* @OnMessage
* public void processGreeting(String message, Session session) {
* System.out.println("Greeting received:" + message);
* }
*
*
*
* For example:
*
*
*
* @OnMessage
* public void processUpload(byte[] b, boolean last, Session session) {
* // process partial data here, which check on last to see if these is more on the way
* }
*
*
*
* Developers should not continue to reference message objects of type {@link java.io.Reader},
* {@link java.nio.ByteBuffer} or {@link java.io.InputStream} after the annotated method has completed, since they may
* be recycled by the implementation.
*
* @author dannycoward
*/
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface OnMessage {
/**
* Specifies the maximum size of message in bytes that the method this annotates will be able to process, or -1 to
* indicate that there is no maximum. The default is -1. This attribute only applies when the annotation is used to
* process whole messages, not to those methods that process messages in parts or use a stream or reader parameter
* to handle the incoming message. If the incoming whole message exceeds this limit, then the implementation
* generates an error and closes the connection using the reason that the message was too big.
*
* @return the maximum size in bytes.
*/
public long maxMessageSize() default -1;
}