/*
* Copyright 2002-2009 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.http.converter;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;
import org.springframework.util.Assert;
/**
* Abstract base class for most {@link HttpMessageConverter} implementations.
*
* <p>This base class adds support for setting supported {@code MediaTypes}, through the {@link
* #setSupportedMediaTypes(List) supportedMediaTypes} bean property. It also adds support for {@code Content-Type} and
* {@code Content-Length} when writing to output messages.
*
* @author Arjen Poutsma
* @since 3.0
*/
public abstract class AbstractHttpMessageConverter<T> implements HttpMessageConverter<T> {
/** Logger available to subclasses */
protected final Log logger = LogFactory.getLog(getClass());
private List<MediaType> supportedMediaTypes = Collections.emptyList();
/**
* Construct an {@code AbstractHttpMessageConverter} with no supported media types.
*
* @see #setSupportedMediaTypes
*/
protected AbstractHttpMessageConverter() {
}
/**
* Construct an {@code AbstractHttpMessageConverter} with one supported media type.
*
* @param supportedMediaType the supported media type
*/
protected AbstractHttpMessageConverter(MediaType supportedMediaType) {
setSupportedMediaTypes(Collections.singletonList(supportedMediaType));
}
/**
* Construct an {@code AbstractHttpMessageConverter} with multiple supported media type.
*
* @param supportedMediaTypes the supported media types
*/
protected AbstractHttpMessageConverter(MediaType... supportedMediaTypes) {
setSupportedMediaTypes(Arrays.asList(supportedMediaTypes));
}
/** Set the list of {@link MediaType} objects supported by this converter. */
public void setSupportedMediaTypes(List<MediaType> supportedMediaTypes) {
Assert.notEmpty(supportedMediaTypes, "'supportedMediaTypes' must not be empty");
this.supportedMediaTypes = new ArrayList<MediaType>(supportedMediaTypes);
}
public List<MediaType> getSupportedMediaTypes() {
return Collections.unmodifiableList(this.supportedMediaTypes);
}
/**
* {@inheritDoc}
*
* <p>This implementation checks if the given class is {@linkplain #supports(Class) supported}, and if the {@linkplain
* #getSupportedMediaTypes() supported media types} {@linkplain MediaType#includes(MediaType) include} the given media
* type.
*/
public boolean canRead(Class<? extends T> clazz, MediaType mediaType) {
return supports(clazz) && isSupported(mediaType);
}
/**
* {@inheritDoc}
*
* <p>This implementation checks if the given class is {@linkplain #supports(Class) supported}, and if the {@linkplain
* #getSupportedMediaTypes() supported media types} {@linkplain MediaType#includes(MediaType) include} the given media
* type.
*/
public boolean canWrite(Class<? extends T> clazz, MediaType mediaType) {
return supports(clazz) && isSupported(mediaType);
}
/**
* Returns true if any of the {@linkplain #setSupportedMediaTypes(List) supported media types} include the given media
* type.
*
* @param mediaType the media type
* @return true if the supported media types include the media type, or if the media type is {@code null}
*/
protected boolean isSupported(MediaType mediaType) {
if (mediaType == null) {
return true;
}
for (MediaType supportedMediaType : getSupportedMediaTypes()) {
if (supportedMediaType.includes(mediaType)) {
return true;
}
}
return false;
}
/**
* Indicates whether the given class is supported by this converter.
*
* @param clazz the class to test for support
* @return <code>true</code> if supported; <code>false</code> otherwise
*/
protected abstract boolean supports(Class<? extends T> clazz);
/**
* {@inheritDoc}
*
* <p>This implementation simple delegates to {@link #readInternal(Class, HttpInputMessage)}. Future implementations
* might add some default behavior, however.
*/
public final T read(Class<T> clazz, HttpInputMessage inputMessage) throws IOException {
return readInternal(clazz, inputMessage);
}
/**
* Abstract template method that reads the actualy object. Invoked from {@link #read(Class, HttpInputMessage)}.
*
* @param clazz the type of object to return
* @param inputMessage the HTTP input message to read from
* @return the converted object
* @throws IOException in case of I/O errors
* @throws HttpMessageNotReadableException in case of conversion errors
*/
protected abstract T readInternal(Class<T> clazz, HttpInputMessage inputMessage)
throws IOException, HttpMessageNotReadableException;
/**
* {@inheritDoc}
*
* <p>This implementation delegates to {@link #getDefaultContentType(Object)} if a content type was not provided, calls
* {@link #getContentLength}, and sets the corresponding headers on the output message. It then calls {@link
* #writeInternal}.
*/
public final void write(T t, MediaType contentType, HttpOutputMessage outputMessage)
throws IOException, HttpMessageNotWritableException {
HttpHeaders headers = outputMessage.getHeaders();
if (contentType == null) {
contentType = getDefaultContentType(t);
}
if (contentType != null) {
headers.setContentType(contentType);
}
Long contentLength = getContentLength(t, contentType);
if (contentLength != null) {
headers.setContentLength(contentLength);
}
writeInternal(t, outputMessage);
outputMessage.getBody().flush();
}
/**
* Returns the default content type for the given type. Called when {@link #write} is invoked without a specified
* content type parameter.
*
* <p>By default, this returns the first element of the {@link #setSupportedMediaTypes(List) supportedMediaTypes}
* property, if any. Can be overriden in subclasses.
*
* @param t the type to return the content type for
* @return the content type, or <code>null</code> if not known
*/
protected MediaType getDefaultContentType(T t) {
List<MediaType> mediaTypes = getSupportedMediaTypes();
return (!mediaTypes.isEmpty() ? mediaTypes.get(0) : null);
}
/**
* Returns the content length for the given type.
*
* <p>By default, this returns {@code null}, meaning that the content length is unknown. Can be overriden in
* subclasses.
*
* @param t the type to return the content length for
* @return the content length, or {@code null} if not known
*/
protected Long getContentLength(T t, MediaType contentType) {
return null;
}
/**
* Abstract template method that writes the actual body. Invoked from {@link #write}.
*
* @param t the object to write to the output message
* @param outputMessage the message to write to
* @throws IOException in case of I/O errors
* @throws HttpMessageNotWritableException in case of conversion errors
*/
protected abstract void writeInternal(T t, HttpOutputMessage outputMessage)
throws IOException, HttpMessageNotWritableException;
}
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