详解自定义SpringMVC的Http信息转换器的使用

package org.springframework.http;

import java.io.IOException;
import java.io.InputStream;

public interface HttpInputMessage extends HttpMessage {

  InputStream getBody() throws IOException;

}

package org.springframework.http;

import java.io.IOException;
import java.io.OutputStream;

public interface HttpOutputMessage extends HttpMessage {

  OutputStream getBody() throws IOException;

}

/*
 * Copyright 2002-2010 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.List;

import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;


public interface HttpMessageConverter<T> {


  boolean canRead(Class<?> clazz, MediaType mediaType);

  boolean canWrite(Class<?> clazz, MediaType mediaType);

  List<MediaType> getSupportedMediaTypes();


  T read(Class<? extends T> clazz, HttpInputMessage inputMessage)
      throws IOException, HttpMessageNotReadableException;


  void write(T t, MediaType contentType, HttpOutputMessage outputMessage)
      throws IOException, HttpMessageNotWritableException;

}

private Object readWithMessageConverters(MethodParameter methodParam, HttpInputMessage inputMessage, Class paramType) throws Exception { 

  MediaType contentType = inputMessage.getHeaders().getContentType(); 
  if (contentType == null) { 
    StringBuilder builder = new StringBuilder(ClassUtils.getShortName(methodParam.getParameterType())); 
    String paramName = methodParam.getParameterName(); 
    if (paramName != null) { 
      builder.append(' '); 
      builder.append(paramName); 
    } 
    throw new HttpMediaTypeNotSupportedException("Cannot extract parameter (" + builder.toString() + "): no Content-Type found"); 
  } 

  List<MediaType> allSupportedMediaTypes = new ArrayList<MediaType>(); 
  if (this.messageConverters != null) { 
    for (HttpMessageConverter<?> messageConverter : this.messageConverters) { 
      allSupportedMediaTypes.addAll(messageConverter.getSupportedMediaTypes()); 
      if (messageConverter.canRead(paramType, contentType)) { 
        if (logger.isDebugEnabled()) { 
          logger.debug("Reading [" + paramType.getName() + "] as \"" + contentType + "\" using [" + messageConverter + "]"); 
        } 
        return messageConverter.read(paramType, inputMessage); 
      } 
    } 
  } 
  throw new HttpMediaTypeNotSupportedException(contentType, allSupportedMediaTypes); 
}

private void writeWithMessageConverters(Object returnValue, HttpInputMessage inputMessage, HttpOutputMessage outputMessage) 
        throws IOException, HttpMediaTypeNotAcceptableException { 
  List<MediaType> acceptedMediaTypes = inputMessage.getHeaders().getAccept(); 
  if (acceptedMediaTypes.isEmpty()) { 
    acceptedMediaTypes = Collections.singletonList(MediaType.ALL); 
  } 
  MediaType.sortByQualityValue(acceptedMediaTypes); 
  Class<?> returnValueType = returnValue.getClass(); 
  List<MediaType> allSupportedMediaTypes = new ArrayList<MediaType>(); 
  if (getMessageConverters() != null) { 
    for (MediaType acceptedMediaType : acceptedMediaTypes) { 
      for (HttpMessageConverter messageConverter : getMessageConverters()) { 
        if (messageConverter.canWrite(returnValueType, acceptedMediaType)) { 
          messageConverter.write(returnValue, acceptedMediaType, outputMessage); 
          if (logger.isDebugEnabled()) { 
            MediaType contentType = outputMessage.getHeaders().getContentType(); 
            if (contentType == null) { 
              contentType = acceptedMediaType; 
            } 
            logger.debug("Written [" + returnValue + "] as \"" + contentType + 
                "\" using [" + messageConverter + "]"); 
          } 
          this.responseArgumentUsed = true; 
          return; 
        } 
      } 
    } 
    for (HttpMessageConverter messageConverter : messageConverters) { 
      allSupportedMediaTypes.addAll(messageConverter.getSupportedMediaTypes()); 
    } 
  } 
  throw new HttpMediaTypeNotAcceptableException(allSupportedMediaTypes); 
}

class CustomJsonHttpMessageConverter implements HttpMessageConverter {

  //Jackson的Json映射类
  private ObjectMapper mapper = new ObjectMapper();

  //该转换器的支持类型：application/json
  private List supportedMediaTypes = Arrays.asList(MediaType.APPLICATION_JSON);

  /**
   * 判断转换器是否可以将输入内容转换成Java类型
   * @param clazz   需要转换的Java类型
   * @param mediaType 该请求的MediaType
   * @return
   */
  @Override
  public boolean canRead(Class clazz, MediaType mediaType) {
    if (mediaType == null) {
      return true;
    }
    for (MediaType supportedMediaType : getSupportedMediaTypes()) {
      if (supportedMediaType.includes(mediaType)) {
        return true;
      }
    }
    return false;
  }

  /**
   * 判断转换器是否可以将Java类型转换成指定输出内容
   * @param clazz   需要转换的Java类型
   * @param mediaType 该请求的MediaType
   * @return
   */
  @Override
  public boolean canWrite(Class clazz, MediaType mediaType) {
    if (mediaType == null || MediaType.ALL.equals(mediaType)) {
      return true;
    }
    for (MediaType supportedMediaType : getSupportedMediaTypes()) {
      if (supportedMediaType.includes(mediaType)) {
        return true;
      }
    }
    return false;
  }

  /**
   * 获得该转换器支持的MediaType
   * @return
   */
  @Override
  public List getSupportedMediaTypes() {
    return supportedMediaTypes;
  }

  /**
   * 读取请求内容，将其中的Json转换成Java对象
   * @param clazz     需要转换的Java类型
   * @param inputMessage 请求对象
   * @return
   * @throws IOException
   * @throws HttpMessageNotReadableException
   */
  @Override
  public Object read(Class clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
    return mapper.readValue(inputMessage.getBody(), clazz);
  }

  /**
   * 将Java对象转换成Json返回内容
   * @param o       需要转换的对象
   * @param contentType  返回类型
   * @param outputMessage 回执对象
   * @throws IOException
   * @throws HttpMessageNotWritableException
   */
  @Override
  public void write(Object o, MediaType contentType, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {
    mapper.writeValue(outputMessage.getBody(), o);
  }
}

@Bean
public MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {
  return new MappingJackson2HttpMessageConverter() {
    //重写writeInternal方法，在返回内容前首先进行加密
    @Override
    protected void writeInternal(Object object,
                   HttpOutputMessage outputMessage) throws IOException,
        HttpMessageNotWritableException {
      //使用Jackson的ObjectMapper将Java对象转换成Json String
      ObjectMapper mapper = new ObjectMapper();
      String json = mapper.writeValueAsString(object);
      LOGGER.error(json);
      //加密
      String result = json + "加密了！";
      LOGGER.error(result);
      //输出
      outputMessage.getBody().write(result.getBytes());
    }
  };
}
 

//添加自定义转换器
@Override
public void configureMessageConverters(List<httpmessageconverter<?>> converters) {
  converters.add(mappingJackson2HttpMessageConverter());
  super.configureMessageConverters(converters);
}