/*
* Copyright 2002-2014 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.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
* @author Juergen Hoeller
* @since 1.0
*/
public abstract class AbstractHttpMessageConverter<T> implements HttpMessageConverter<T> {
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);
}
/**
* 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<?> clazz, MediaType mediaType) {
return supports(clazz) && canRead(mediaType);
}
/**
* Returns true if any of the {@linkplain #setSupportedMediaTypes(List) supported media types}
* include the given media type.
* @param mediaType the media type to read, can be {@code null} if not specified.
* Typically the value of a {@code Content-Type} header.
* @return {@code true} if the supported media types include the media type,
* or if the media type is {@code null}
*/
protected boolean canRead(MediaType mediaType) {
if (mediaType == null) {
return true;
}
for (MediaType supportedMediaType : getSupportedMediaTypes()) {
if (supportedMediaType.includes(mediaType)) {
return true;
}
}
return false;
}
/**
* 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<?> clazz, MediaType mediaType) {
return supports(clazz) && canWrite(mediaType);
}
/**
* Returns {@code true} if the given media type includes any of the
* {@linkplain #setSupportedMediaTypes(List) supported media types}.
* @param mediaType the media type to write, can be {@code null} if not specified.
* Typically the value of an {@code Accept} header.
* @return {@code true} if the supported media types are compatible with the media type,
* or if the media type is {@code null}
*/
protected boolean canWrite(MediaType mediaType) {
if (mediaType == null || MediaType.ALL.equals(mediaType)) {
return true;
}
for (MediaType supportedMediaType : getSupportedMediaTypes()) {
if (supportedMediaType.isCompatibleWith(mediaType)) {
return true;
}
}
return false;
}
/**
* This implementation simple delegates to {@link #readInternal(Class, HttpInputMessage)}.
* Future implementations might add some default behavior, however.
*/
public final T read(Class<? extends T> clazz, HttpInputMessage inputMessage) throws IOException {
return readInternal(clazz, inputMessage);
}
/**
* 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 (headers.getContentType() == null) {
MediaType contentTypeToUse = contentType;
if (contentType == null || contentType.isWildcardType() || contentType.isWildcardSubtype()) {
contentTypeToUse = getDefaultContentType(t);
}
if (contentTypeToUse != null) {
headers.setContentType(contentTypeToUse);
}
}
if (headers.getContentLength() == -1) {
Long contentLength = getContentLength(t, headers.getContentType());
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 overridden in subclasses.
* @param t the type to return the content type for
* @return the content type, or {@code null} if not known
*/
protected MediaType getDefaultContentType(T t) throws IOException {
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 overridden 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) throws IOException {
return null;
}
/**
* Indicates whether the given class is supported by this converter.
* @param clazz the class to test for support
* @return {@code true} if supported; {@code false} otherwise
*/
protected abstract boolean supports(Class<?> clazz);
/**
* Abstract template method that reads the actual object. Invoked from {@link #read}.
* @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<? extends T> clazz, HttpInputMessage inputMessage)
throws IOException, HttpMessageNotReadableException;
/**
* 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 HTTP output 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;
}