消息轉(zhuǎn)換器定義

我們可以通過重寫 configureMessageConverters()方法（替換Spring MVC創(chuàng)建的默認(rèn)轉(zhuǎn)換器）或重寫extendMessageConverters()方法（自定義默認(rèn)轉(zhuǎn)換器或向默認(rèn)轉(zhuǎn)換器添加其他轉(zhuǎn)換器）在Java配置中自定義 HttpMessageConverter。

HttpMessageConverter

消息轉(zhuǎn)換器 HttpMessageConverter 借口定義如下:

public interface HttpMessageConverter {

	/**
	 * Indicates whether the given class can be read by this converter.
	 * @param clazz the class to test for readability
	 * @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 readable; {@code false} otherwise
	 */
	boolean canRead(Class clazz, @Nullable MediaType mediaType);

	/**
	 * Indicates whether the given class can be written by this converter.
	 * @param clazz the class to test for writability
	 * @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 writable; {@code false} otherwise
	 */
	boolean canWrite(Class clazz, @Nullable MediaType mediaType);

	/**
	 * Return the list of media types supported by this converter. The list may
	 * not apply to every possible target element type and calls to this method
	 * should typically be guarded via {@link #canWrite(Class, MediaType)
	 * canWrite(clazz, null}. The list may also exclude MIME types supported
	 * only for a specific class. Alternatively, use
	 * {@link #getSupportedMediaTypes(Class)} for a more precise list.
	 * @return the list of supported media types
	 */
	List getSupportedMediaTypes();

	/**
	 * Return the list of media types supported by this converter for the given
	 * class. The list may differ from {@link #getSupportedMediaTypes()} if the
	 * converter does not support the given Class or if it supports it only for
	 * a subset of media types.
	 * @param clazz the type of class to check
	 * @return the list of media types supported for the given class
	 * @since 5.3.4
	 */
	default List getSupportedMediaTypes(Class clazz) {
		return (canRead(clazz, null) || canWrite(clazz, null) ?
				getSupportedMediaTypes() : Collections.emptyList());
	}

	/**
	 * Read an object of the given type from the given input message, and returns it.
	 * @param clazz the type of object to return. This type must have previously been passed to the
	 * {@link #canRead canRead} method of this interface, which must have returned {@code true}.
	 * @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
	 */
	T read(Class clazz, HttpInputMessage inputMessage)
			throws IOException, HttpMessageNotReadableException;

	/**
	 * Write an given object to the given output message.
	 * @param t the object to write to the output message. The type of this object must have previously been
	 * passed to the {@link #canWrite canWrite} method of this interface, which must have returned {@code true}.
	 * @param contentType the content type to use when writing. May be {@code null} to indicate that the
	 * default content type of the converter must be used. If not {@code null}, this media type must have
	 * previously been passed to the {@link #canWrite canWrite} method of this interface, which must have
	 * returned {@code true}.
	 * @param outputMessage the message to write to
	 * @throws IOException in case of I/O errors
	 * @throws HttpMessageNotWritableException in case of conversion errors
	 */
	void write(T t, @Nullable MediaType contentType, HttpOutputMessage outputMessage)
			throws IOException, HttpMessageNotWritableException;

}
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自定義消息轉(zhuǎn)換器

下面是一個簡單的消息轉(zhuǎn)換器定義，代碼如下:

@Configuration
@EnableWebMvc
public class WebConfiguration implements WebMvcConfigurer {

    @Override
    public void configureMessageConverters(List> converters) {
        Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder()
                .indentOutput(true)
                .dateFormat(new SimpleDateFormat("yyyy-MM-dd"))
                .modulesToInstall(new ParameterNamesModule());
        converters.add(new MappingJackson2HttpMessageConverter(builder.build()));
        converters.add(new MappingJackson2XmlHttpMessageConverter(builder.createXmlMapper(true).build()));
    }
}
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在前面的示例中，Jackson2ObjectMapperBuilder 用于為 MappingJackson2HttpMessageConverter 和MappingJackson2XmlHttpMessageConverter 創(chuàng)建公共配置，啟用縮進(jìn)、自定義日期格式和jackson模塊參數(shù)名稱注冊，這增加了對訪問參數(shù)名稱的支持（Java8中添加的一個特性）。

配置 FastJson 為默認(rèn) JSON 解析器

其實我們在項目最最常用的還是 FastJSON 作為 Spring MVC 的默認(rèn) JSON 解析器。具體的配置如下:

		  class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
	
		
			
				text/html;charset=UTF-8
				application/json
				application/xml;charset=UTF-8
			
		

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參考資料

• docs.spring.io/spring-fram…

• blog.csdn.net/qq_37292960…

作者：老鄭_
鏈接：https://juejin.cn/post/7019692901454069790
來源：稀土掘金
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