javax.websocket.OnMessage Maven / Gradle / Ivy

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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 {@link 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;
}