ConversionService JSR-356 Encoder/Decoder adapters

Develop support class allowing JSR-356 Encoder and Decoder interfaces to delegate to Spring's ConversionService. Issue: SPR-10694

Author: philwebb

spring-websocket/src/main/java/org/springframework/web/socket/adapter/ConvertingEncoderDecoderSupport.java

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+/*
+ * Copyright 2002-2013 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
+ *
+ * http://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.socket.adapter;
+
+import java.nio.ByteBuffer;
+
+import javax.websocket.DecodeException;
+import javax.websocket.Decoder;
+import javax.websocket.EncodeException;
+import javax.websocket.Encoder;
+import javax.websocket.EndpointConfig;
+
+import org.springframework.beans.BeansException;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.core.GenericTypeResolver;
+import org.springframework.core.convert.ConversionException;
+import org.springframework.core.convert.ConversionService;
+import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.util.Assert;
+import org.springframework.web.context.ContextLoader;
+
+/**
+ * Base class that can be used to implement a standard {@link javax.websocket.Encoder}
+ * and/or {@link javax.websocket.Decoder}. It provides encode and decode method
+ * implementations that delegate to a Spring {@link ConversionService}.
+ *
+ * <p>By default, this class looks up a {@link ConversionService} registered in the
+ * {@link #getApplicationContext() active ApplicationContext} under
+ * the name {@code 'webSocketConversionService'}. This works fine for both client
+ * and server endpoints, in a Servlet container environment. If not running in a
+ * Servlet container, subclasses will need to override the
+ * {@link #getConversionService()} method to provide an alternative lookup strategy.
+ *
+ * <p>Subclasses can extend this class and should also implement one or
+ * both of {@link javax.websocket.Encoder} and {@link javax.websocket.Decoder}.
+ * For convenience {@link ConvertingEncoderDecoderSupport.BinaryEncoder},
+ * {@link ConvertingEncoderDecoderSupport.BinaryDecoder},
+ * {@link ConvertingEncoderDecoderSupport.TextEncoder} and
+ * {@link ConvertingEncoderDecoderSupport.TextDecoder} subclasses are provided.
+ *
+ * <p>Since JSR-356 only allows Encoder/Decoder to be registered by type, instances
+ * of this class are therefore managed by the WebSocket runtime, and do not need to
+ * be registered as Spring Beans. They can, however, by injected with Spring-managed
+ * dependencies via {@link Autowired @Autowire}.
+ *
+ * <p>Converters to convert between the {@link #getType() type} and {@code String} or
+ * {@code ByteBuffer} should be registered.
+ *
+ * @author Phillip Webb
+ * @since 4.0
+ *
+ * @param <T> The type being converted to (for Encoder) or from (for Decoder)
+ * @param <M> The WebSocket message type ({@link String} or {@link ByteBuffer})
+ *
+ * @see ConvertingEncoderDecoderSupport.BinaryEncoder
+ * @see ConvertingEncoderDecoderSupport.BinaryDecoder
+ * @see ConvertingEncoderDecoderSupport.TextEncoder
+ * @see ConvertingEncoderDecoderSupport.TextDecoder
+ */
+public abstract class ConvertingEncoderDecoderSupport<T, M> {
+
+private static final String CONVERSION_SERVICE_BEAN_NAME = "webSocketConversionService";
+
+
+/**
+ * @see javax.websocket.Encoder#init(EndpointConfig)
+ * @see javax.websocket.Decoder#init(EndpointConfig)
+ */
+public void init(EndpointConfig config) {
+ApplicationContext applicationContext = getApplicationContext();
+if (applicationContext != null && applicationContext instanceof ConfigurableApplicationContext) {
+ConfigurableListableBeanFactory beanFactory =
+((ConfigurableApplicationContext) applicationContext).getBeanFactory();
+beanFactory.autowireBean(this);
+}
+}
+
+/**
+ * @see javax.websocket.Encoder#destroy()
+ * @see javax.websocket.Decoder#destroy()
+ */
+public void destroy() {
+}
+
+/**
+ * Strategy method used to obtain the {@link ConversionService}. By default this
+ * method expects a bean named {@code 'webSocketConversionService'} in the
+ * {@link #getApplicationContext() active ApplicationContext}.
+ * @return the {@link ConversionService} (never null)
+ */
+protected ConversionService getConversionService() {
+ApplicationContext applicationContext = getApplicationContext();
+Assert.state(applicationContext != null,
+"Unable to locate the Spring ApplicationContext");
+try {
+return applicationContext.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class);
+}
+catch (BeansException ex) {
+throw new IllegalStateException(
+"Unable to find ConversionService, please configure a '"
++ CONVERSION_SERVICE_BEAN_NAME + "' or override getConversionService()", ex);
+}
+}
+
+/**
+ * Returns the active {@link ApplicationContext}. Be default this method obtains
+ * the context via {@link ContextLoader#getCurrentWebApplicationContext()}, which
+ * finds the ApplicationContext loaded via {@link ContextLoader} typically in a
+ * Servlet container environment. When not running in a Servlet container and
+ * not using {@link ContextLoader}, this method should be overridden.
+ * @return the {@link ApplicationContext} or {@code null}
+ */
+protected ApplicationContext getApplicationContext() {
+return ContextLoader.getCurrentWebApplicationContext();
+}
+
+/**
+ * Returns the type being converted. By default the type is resolved using
+ * the generic arguments of the class.
+ */
+protected TypeDescriptor getType() {
+return TypeDescriptor.valueOf(resolveTypeArguments()[0]);
+}
+
+/**
+ * Returns the websocket message type. By default the type is resolved using
+ * the generic arguments of the class.
+ */
+protected TypeDescriptor getMessageType() {
+return TypeDescriptor.valueOf(resolveTypeArguments()[1]);
+}
+
+private Class<?>[] resolveTypeArguments() {
+return GenericTypeResolver.resolveTypeArguments(getClass(),
+ConvertingEncoderDecoderSupport.class);
+}
+
+/**
+ * @see javax.websocket.Encoder.Text#encode(Object)
+ * @see javax.websocket.Encoder.Binary#encode(Object)
+ */
+@SuppressWarnings("unchecked")
+public M encode(T object) throws EncodeException {
+try {
+return (M) getConversionService().convert(object, getType(), getMessageType());
+}
+catch (ConversionException ex) {
+throw new EncodeException(object, "Unable to encode websocket message using ConversionService", ex);
+}
+}
+
+/**
+ * @see javax.websocket.Decoder.Text#willDecode(String)
+ * @see javax.websocket.Decoder.Binary#willDecode(ByteBuffer)
+ */
+public boolean willDecode(M bytes) {
+return getConversionService().canConvert(getType(), getMessageType());
+}
+
+/**
+ * @see javax.websocket.Decoder.Text#decode(String)
+ * @see javax.websocket.Decoder.Binary#decode(ByteBuffer)
+ */
+@SuppressWarnings("unchecked")
+public T decode(M message) throws DecodeException {
+try {
+return (T) getConversionService().convert(message, getMessageType(), getType());
+}
+catch (ConversionException ex) {
+if (message instanceof String) {
+throw new DecodeException((String) message, "Unable to decode " +
+"websocket message using ConversionService", ex);
+}
+if (message instanceof ByteBuffer) {
+throw new DecodeException((ByteBuffer) message, "Unable to decode " +
+"websocket message using ConversionService", ex);
+}
+throw ex;
+}
+}
+
+
+/**
+ * A Binary {@link javax.websocket.Encoder.Binary javax.websocket.Encoder} that
+ * delegates to Spring's conversion service. See
+ * {@link ConvertingEncoderDecoderSupport} for details.
+ *
+ * @param <T> The type that this Encoder can convert to.
+ */
+public static abstract class BinaryEncoder<T> extends
+ConvertingEncoderDecoderSupport<T, ByteBuffer> implements Encoder.Binary<T> {
+}
+
+
+/**
+ * A Binary {@link javax.websocket.Encoder.Binary javax.websocket.Encoder} that delegates
+ * to Spring's conversion service. See {@link ConvertingEncoderDecoderSupport} for
+ * details.
+ *
+ * @param <T> The type that this Decoder can convert from.
+ */
+public static abstract class BinaryDecoder<T> extends
+ConvertingEncoderDecoderSupport<T, ByteBuffer> implements Decoder.Binary<T> {
+}
+
+
+/**
+ * A Text {@link javax.websocket.Encoder.Text javax.websocket.Encoder} that delegates
+ * to Spring's conversion service. See {@link ConvertingEncoderDecoderSupport} for
+ * details.
+ *
+ * @param <T> The type that this Encoder can convert to.
+ */
+public static abstract class TextEncoder<T> extends
+ConvertingEncoderDecoderSupport<T, String> implements Encoder.Text<T> {
+}
+
+
+/**
+ * A Text {@link javax.websocket.Encoder.Text javax.websocket.Encoder} that delegates
+ * to Spring's conversion service. See {@link ConvertingEncoderDecoderSupport} for
+ * details.
+ *
+ * @param <T> The type that this Decoder can convert from.
+ */
+public static abstract class TextDecoder<T> extends
+ConvertingEncoderDecoderSupport<T, String> implements Decoder.Text<T> {
+}
+
+}

spring-websocket/src/test/java/org/springframework/web/socket/ContextLoaderTestUtils.java

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+/*
+ * Copyright 2002-2013 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
+ *
+ * http://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.socket;
+
+import java.lang.reflect.Field;
+import java.util.Map;
+
+import org.springframework.web.context.ContextLoader;
+import org.springframework.web.context.WebApplicationContext;
+
+/**
+ * General test utilities for manipulating the {@link ContextLoader}.
+ *
+ * @author Phillip Webb
+ */
+public class ContextLoaderTestUtils {
+
+private static Map<ClassLoader, WebApplicationContext> currentContextPerThread = getCurrentContextPerThreadFromContextLoader();
+
+public static void setCurrentWebApplicationContext(WebApplicationContext applicationContext) {
+setCurrentWebApplicationContext(Thread.currentThread().getContextClassLoader(), applicationContext);
+}
+
+public static void setCurrentWebApplicationContext(ClassLoader classLoader, WebApplicationContext applicationContext) {
+if(applicationContext != null) {
+currentContextPerThread.put(classLoader, applicationContext);
+} else {
+currentContextPerThread.remove(classLoader);
+}
+}
+
+@SuppressWarnings("unchecked")
+private static Map<ClassLoader, WebApplicationContext> getCurrentContextPerThreadFromContextLoader() {
+try {
+Field field = ContextLoader.class.getDeclaredField("currentContextPerThread");
+field.setAccessible(true);
+return (Map<ClassLoader, WebApplicationContext>) field.get(null);
+}
+catch (Exception ex) {
+throw new IllegalStateException(ex);
+}
+}
+
+}