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
This commit is contained in:
Phillip Webb
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/*
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* Copyright 2002-2013 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.springframework.web.socket.adapter;
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import java.nio.ByteBuffer;
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import javax.websocket.DecodeException;
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import javax.websocket.Decoder;
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import javax.websocket.EncodeException;
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import javax.websocket.Encoder;
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import javax.websocket.EndpointConfig;
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import org.springframework.beans.BeansException;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
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import org.springframework.context.ApplicationContext;
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import org.springframework.context.ConfigurableApplicationContext;
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import org.springframework.core.GenericTypeResolver;
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import org.springframework.core.convert.ConversionException;
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import org.springframework.core.convert.ConversionService;
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import org.springframework.core.convert.TypeDescriptor;
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import org.springframework.util.Assert;
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import org.springframework.web.context.ContextLoader;
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/**
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* Base class that can be used to implement a standard {@link javax.websocket.Encoder}
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* and/or {@link javax.websocket.Decoder}. It provides encode and decode method
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* implementations that delegate to a Spring {@link ConversionService}.
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*
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* <p>By default, this class looks up a {@link ConversionService} registered in the
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* {@link #getApplicationContext() active ApplicationContext} under
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* the name {@code 'webSocketConversionService'}. This works fine for both client
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* and server endpoints, in a Servlet container environment. If not running in a
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* Servlet container, subclasses will need to override the
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* {@link #getConversionService()} method to provide an alternative lookup strategy.
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*
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* <p>Subclasses can extend this class and should also implement one or
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* both of {@link javax.websocket.Encoder} and {@link javax.websocket.Decoder}.
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* For convenience {@link ConvertingEncoderDecoderSupport.BinaryEncoder},
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* {@link ConvertingEncoderDecoderSupport.BinaryDecoder},
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* {@link ConvertingEncoderDecoderSupport.TextEncoder} and
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* {@link ConvertingEncoderDecoderSupport.TextDecoder} subclasses are provided.
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*
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* <p>Since JSR-356 only allows Encoder/Decoder to be registered by type, instances
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* of this class are therefore managed by the WebSocket runtime, and do not need to
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* be registered as Spring Beans. They can, however, by injected with Spring-managed
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* dependencies via {@link Autowired @Autowire}.
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*
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* <p>Converters to convert between the {@link #getType() type} and {@code String} or
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* {@code ByteBuffer} should be registered.
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*
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* @author Phillip Webb
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* @since 4.0
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*
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* @param <T> The type being converted to (for Encoder) or from (for Decoder)
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* @param <M> The WebSocket message type ({@link String} or {@link ByteBuffer})
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*
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* @see ConvertingEncoderDecoderSupport.BinaryEncoder
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* @see ConvertingEncoderDecoderSupport.BinaryDecoder
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* @see ConvertingEncoderDecoderSupport.TextEncoder
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* @see ConvertingEncoderDecoderSupport.TextDecoder
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*/
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public abstract class ConvertingEncoderDecoderSupport<T, M> {
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private static final String CONVERSION_SERVICE_BEAN_NAME = "webSocketConversionService";
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/**
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* @see javax.websocket.Encoder#init(EndpointConfig)
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* @see javax.websocket.Decoder#init(EndpointConfig)
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*/
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public void init(EndpointConfig config) {
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ApplicationContext applicationContext = getApplicationContext();
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if (applicationContext != null && applicationContext instanceof ConfigurableApplicationContext) {
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ConfigurableListableBeanFactory beanFactory =
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((ConfigurableApplicationContext) applicationContext).getBeanFactory();
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beanFactory.autowireBean(this);
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}
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}
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/**
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* @see javax.websocket.Encoder#destroy()
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* @see javax.websocket.Decoder#destroy()
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*/
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public void destroy() {
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}
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/**
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* Strategy method used to obtain the {@link ConversionService}. By default this
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* method expects a bean named {@code 'webSocketConversionService'} in the
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* {@link #getApplicationContext() active ApplicationContext}.
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* @return the {@link ConversionService} (never null)
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*/
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protected ConversionService getConversionService() {
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ApplicationContext applicationContext = getApplicationContext();
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Assert.state(applicationContext != null,
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"Unable to locate the Spring ApplicationContext");
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try {
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return applicationContext.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class);
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}
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catch (BeansException ex) {
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throw new IllegalStateException(
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"Unable to find ConversionService, please configure a '"
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+ CONVERSION_SERVICE_BEAN_NAME + "' or override getConversionService()", ex);
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}
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}
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/**
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* Returns the active {@link ApplicationContext}. Be default this method obtains
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* the context via {@link ContextLoader#getCurrentWebApplicationContext()}, which
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* finds the ApplicationContext loaded via {@link ContextLoader} typically in a
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* Servlet container environment. When not running in a Servlet container and
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* not using {@link ContextLoader}, this method should be overridden.
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* @return the {@link ApplicationContext} or {@code null}
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*/
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protected ApplicationContext getApplicationContext() {
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return ContextLoader.getCurrentWebApplicationContext();
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}
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/**
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* Returns the type being converted. By default the type is resolved using
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* the generic arguments of the class.
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*/
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protected TypeDescriptor getType() {
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return TypeDescriptor.valueOf(resolveTypeArguments()[0]);
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}
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/**
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* Returns the websocket message type. By default the type is resolved using
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* the generic arguments of the class.
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*/
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protected TypeDescriptor getMessageType() {
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return TypeDescriptor.valueOf(resolveTypeArguments()[1]);
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}
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private Class<?>[] resolveTypeArguments() {
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return GenericTypeResolver.resolveTypeArguments(getClass(),
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ConvertingEncoderDecoderSupport.class);
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}
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/**
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* @see javax.websocket.Encoder.Text#encode(Object)
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* @see javax.websocket.Encoder.Binary#encode(Object)
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*/
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@SuppressWarnings("unchecked")
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public M encode(T object) throws EncodeException {
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try {
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return (M) getConversionService().convert(object, getType(), getMessageType());
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}
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catch (ConversionException ex) {
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throw new EncodeException(object, "Unable to encode websocket message using ConversionService", ex);
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}
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}
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/**
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* @see javax.websocket.Decoder.Text#willDecode(String)
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* @see javax.websocket.Decoder.Binary#willDecode(ByteBuffer)
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*/
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public boolean willDecode(M bytes) {
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return getConversionService().canConvert(getType(), getMessageType());
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}
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/**
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* @see javax.websocket.Decoder.Text#decode(String)
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* @see javax.websocket.Decoder.Binary#decode(ByteBuffer)
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*/
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@SuppressWarnings("unchecked")
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public T decode(M message) throws DecodeException {
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try {
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return (T) getConversionService().convert(message, getMessageType(), getType());
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}
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catch (ConversionException ex) {
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if (message instanceof String) {
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throw new DecodeException((String) message, "Unable to decode " +
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"websocket message using ConversionService", ex);
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}
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if (message instanceof ByteBuffer) {
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throw new DecodeException((ByteBuffer) message, "Unable to decode " +
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"websocket message using ConversionService", ex);
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}
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throw ex;
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}
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}
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/**
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* A Binary {@link javax.websocket.Encoder.Binary javax.websocket.Encoder} that
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* delegates to Spring's conversion service. See
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* {@link ConvertingEncoderDecoderSupport} for details.
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*
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* @param <T> The type that this Encoder can convert to.
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*/
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public static abstract class BinaryEncoder<T> extends
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ConvertingEncoderDecoderSupport<T, ByteBuffer> implements Encoder.Binary<T> {
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}
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/**
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* A Binary {@link javax.websocket.Encoder.Binary javax.websocket.Encoder} that delegates
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* to Spring's conversion service. See {@link ConvertingEncoderDecoderSupport} for
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* details.
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*
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* @param <T> The type that this Decoder can convert from.
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*/
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public static abstract class BinaryDecoder<T> extends
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ConvertingEncoderDecoderSupport<T, ByteBuffer> implements Decoder.Binary<T> {
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}
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/**
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* A Text {@link javax.websocket.Encoder.Text javax.websocket.Encoder} that delegates
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* to Spring's conversion service. See {@link ConvertingEncoderDecoderSupport} for
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* details.
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*
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* @param <T> The type that this Encoder can convert to.
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*/
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public static abstract class TextEncoder<T> extends
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ConvertingEncoderDecoderSupport<T, String> implements Encoder.Text<T> {
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}
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/**
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* A Text {@link javax.websocket.Encoder.Text javax.websocket.Encoder} that delegates
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* to Spring's conversion service. See {@link ConvertingEncoderDecoderSupport} for
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* details.
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*
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* @param <T> The type that this Decoder can convert from.
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*/
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public static abstract class TextDecoder<T> extends
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ConvertingEncoderDecoderSupport<T, String> implements Decoder.Text<T> {
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}
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}
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