Java tutorial
/* * Copyright 2002-2017 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 * * https://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 org.springframework.web.servlet.mvc.method.annotation; import java.io.IOException; import java.nio.charset.StandardCharsets; import java.util.Collections; import java.util.LinkedHashSet; import java.util.Set; import org.springframework.http.HttpHeaders; import org.springframework.http.MediaType; import org.springframework.http.server.ServerHttpResponse; import org.springframework.lang.Nullable; import org.springframework.util.ObjectUtils; import org.springframework.util.StringUtils; /** * A specialization of {@link ResponseBodyEmitter} for sending * <a href="https://www.w3.org/TR/eventsource/">Server-Sent Events</a>. * * @author Rossen Stoyanchev * @author Juergen Hoeller * @since 4.2 */ public class SseEmitter extends ResponseBodyEmitter { static final MediaType TEXT_PLAIN = new MediaType("text", "plain", StandardCharsets.UTF_8); static final MediaType UTF8_TEXT_EVENTSTREAM = new MediaType("text", "event-stream", StandardCharsets.UTF_8); /** * Create a new SseEmitter instance. */ public SseEmitter() { super(); } /** * Create a SseEmitter with a custom timeout value. * <p>By default not set in which case the default configured in the MVC * Java Config or the MVC namespace is used, or if that's not set, then the * timeout depends on the default of the underlying server. * @param timeout timeout value in milliseconds * @since 4.2.2 */ public SseEmitter(Long timeout) { super(timeout); } @Override protected void extendResponse(ServerHttpResponse outputMessage) { super.extendResponse(outputMessage); HttpHeaders headers = outputMessage.getHeaders(); if (headers.getContentType() == null) { headers.setContentType(UTF8_TEXT_EVENTSTREAM); } } /** * Send the object formatted as a single SSE "data" line. It's equivalent to: * <pre> * // static import of SseEmitter.* * * SseEmitter emitter = new SseEmitter(); * emitter.send(event().data(myObject)); * </pre> * * <p>Please, see {@link ResponseBodyEmitter#send(Object) parent Javadoc} * for important notes on exception handling. * * @param object the object to write * @throws IOException raised when an I/O error occurs * @throws java.lang.IllegalStateException wraps any other errors */ @Override public void send(Object object) throws IOException { send(object, null); } /** * Send the object formatted as a single SSE "data" line. It's equivalent to: * <pre> * // static import of SseEmitter.* * * SseEmitter emitter = new SseEmitter(); * emitter.send(event().data(myObject, MediaType.APPLICATION_JSON)); * </pre> * * <p>Please, see {@link ResponseBodyEmitter#send(Object) parent Javadoc} * for important notes on exception handling. * * @param object the object to write * @param mediaType a MediaType hint for selecting an HttpMessageConverter * @throws IOException raised when an I/O error occurs */ @Override public void send(Object object, @Nullable MediaType mediaType) throws IOException { send(event().data(object, mediaType)); } /** * Send an SSE event prepared with the given builder. For example: * <pre> * // static import of SseEmitter * SseEmitter emitter = new SseEmitter(); * emitter.send(event().name("update").id("1").data(myObject)); * </pre> * @param builder a builder for an SSE formatted event. * @throws IOException raised when an I/O error occurs */ public void send(SseEventBuilder builder) throws IOException { Set<DataWithMediaType> dataToSend = builder.build(); synchronized (this) { for (DataWithMediaType entry : dataToSend) { super.send(entry.getData(), entry.getMediaType()); } } } @Override public String toString() { return "SseEmitter@" + ObjectUtils.getIdentityHexString(this); } public static SseEventBuilder event() { return new SseEventBuilderImpl(); } /** * A builder for an SSE event. */ public interface SseEventBuilder { /** * Add an SSE "id" line. */ SseEventBuilder id(String id); /** * Add an SSE "event" line. */ SseEventBuilder name(String eventName); /** * Add an SSE "retry" line. */ SseEventBuilder reconnectTime(long reconnectTimeMillis); /** * Add an SSE "comment" line. */ SseEventBuilder comment(String comment); /** * Add an SSE "data" line. */ SseEventBuilder data(Object object); /** * Add an SSE "data" line. */ SseEventBuilder data(Object object, @Nullable MediaType mediaType); /** * Return one or more Object-MediaType pairs to write via * {@link #send(Object, MediaType)}. * @since 4.2.3 */ Set<DataWithMediaType> build(); } /** * Default implementation of SseEventBuilder. */ private static class SseEventBuilderImpl implements SseEventBuilder { private final Set<DataWithMediaType> dataToSend = new LinkedHashSet<>(4); @Nullable private StringBuilder sb; @Override public SseEventBuilder id(String id) { append("id:").append(id).append("\n"); return this; } @Override public SseEventBuilder name(String name) { append("event:").append(name).append("\n"); return this; } @Override public SseEventBuilder reconnectTime(long reconnectTimeMillis) { append("retry:").append(String.valueOf(reconnectTimeMillis)).append("\n"); return this; } @Override public SseEventBuilder comment(String comment) { append(":").append(comment).append("\n"); return this; } @Override public SseEventBuilder data(Object object) { return data(object, null); } @Override public SseEventBuilder data(Object object, @Nullable MediaType mediaType) { append("data:"); saveAppendedText(); this.dataToSend.add(new DataWithMediaType(object, mediaType)); append("\n"); return this; } SseEventBuilderImpl append(String text) { if (this.sb == null) { this.sb = new StringBuilder(); } this.sb.append(text); return this; } @Override public Set<DataWithMediaType> build() { if (!StringUtils.hasLength(this.sb) && this.dataToSend.isEmpty()) { return Collections.emptySet(); } append("\n"); saveAppendedText(); return this.dataToSend; } private void saveAppendedText() { if (this.sb != null) { this.dataToSend.add(new DataWithMediaType(this.sb.toString(), TEXT_PLAIN)); this.sb = null; } } } }