produces：指定响应体返回类型和编码
使用前：
使用后：
官方文档：
produces
public abstract java.lang.String[] produces
The producible media types of the mapped request, narrowing the primary mapping.
The format is a single media type or a sequence of media types, with a request only mapped if the Accept matches one of these media types. Examples:
produces = "text/plain"
produces = {"text/plain", "application/*"}
produces = MediaType.APPLICATION_JSON_UTF8_VALUE
It affects the actual content type written, for example to produce a JSON response with UTF-8 encoding, MediaType.APPLICATION_JSON_UTF8_VALUE should be used.
Expressions can be negated by using the "!" operator, as in "!text/plain", which matches all requests with a Accept other than "text/plain".
Supported at the type level as well as at the method level! When used at the type level, all method-level mappings override this produces restriction.
See Also:
MediaType
Default:
{}定义内容：MediaType类
Fields
Modifier and Type Field and Description
static MediaType ALL
Public constant media type that includes all media ranges (i.e.
static java.lang.String ALL_VALUE
A String equivalent of ALL.
static MediaType APPLICATION_ATOM_XML
Public constant media type for application/atom+xml.
static java.lang.String APPLICATION_ATOM_XML_VALUE
A String equivalent of APPLICATION_ATOM_XML.
static MediaType APPLICATION_FORM_URLENCODED
Public constant media type for application/x-www-form-urlencoded.
static java.lang.String APPLICATION_FORM_URLENCODED_VALUE
A String equivalent of APPLICATION_FORM_URLENCODED.
static MediaType APPLICATION_JSON
Public constant media type for application/json.
static MediaType APPLICATION_JSON_UTF8
Public constant media type for application/json;charset=UTF-8.
static java.lang.String APPLICATION_JSON_UTF8_VALUE
A String equivalent of APPLICATION_JSON_UTF8.
static java.lang.String APPLICATION_JSON_VALUE
A String equivalent of APPLICATION_JSON.
static MediaType APPLICATION_OCTET_STREAM
Public constant media type for application/octet-stream.
static java.lang.String APPLICATION_OCTET_STREAM_VALUE
A String equivalent of APPLICATION_OCTET_STREAM.
static MediaType APPLICATION_PDF
Public constant media type for application/pdf.
static java.lang.String APPLICATION_PDF_VALUE
A String equivalent of APPLICATION_PDF.
static MediaType APPLICATION_PROBLEM_JSON
Public constant media type for application/problem+json.
static MediaType APPLICATION_PROBLEM_JSON_UTF8
Public constant media type for application/problem+json.
static java.lang.String APPLICATION_PROBLEM_JSON_UTF8_VALUE
A String equivalent of APPLICATION_PROBLEM_JSON_UTF8.
static java.lang.String APPLICATION_PROBLEM_JSON_VALUE
A String equivalent of APPLICATION_PROBLEM_JSON.
static MediaType APPLICATION_PROBLEM_XML
Public constant media type for application/problem+xml.
static java.lang.String APPLICATION_PROBLEM_XML_VALUE
A String equivalent of APPLICATION_PROBLEM_XML.
static MediaType APPLICATION_RSS_XML
Public constant media type for application/rss+xml.
static java.lang.String APPLICATION_RSS_XML_VALUE
A String equivalent of APPLICATION_RSS_XML.
static MediaType APPLICATION_STREAM_JSON
Public constant media type for application/stream+json.
static java.lang.String APPLICATION_STREAM_JSON_VALUE
A String equivalent of APPLICATION_STREAM_JSON.
static MediaType APPLICATION_XHTML_XML
Public constant media type for application/xhtml+xml.
static java.lang.String APPLICATION_XHTML_XML_VALUE
A String equivalent of APPLICATION_XHTML_XML.
static MediaType APPLICATION_XML
Public constant media type for application/xml.
static java.lang.String APPLICATION_XML_VALUE
A String equivalent of APPLICATION_XML.
static MediaType IMAGE_GIF
Public constant media type for image/gif.
static java.lang.String IMAGE_GIF_VALUE
A String equivalent of IMAGE_GIF.
static MediaType IMAGE_JPEG
Public constant media type for image/jpeg.
static java.lang.String IMAGE_JPEG_VALUE
A String equivalent of IMAGE_JPEG.
static MediaType IMAGE_PNG
Public constant media type for image/png.
static java.lang.String IMAGE_PNG_VALUE
A String equivalent of IMAGE_PNG.
static MediaType MULTIPART_FORM_DATA
Public constant media type for multipart/form-data.
static java.lang.String MULTIPART_FORM_DATA_VALUE
A String equivalent of MULTIPART_FORM_DATA.
static java.util.Comparator<MediaType> QUALITY_VALUE_COMPARATOR
Comparator used by sortByQualityValue(List).
static java.util.Comparator<MediaType> SPECIFICITY_COMPARATOR
Comparator used by sortBySpecificity(List).
static MediaType TEXT_EVENT_STREAM
Public constant media type for text/event-stream.
static java.lang.String TEXT_EVENT_STREAM_VALUE
A String equivalent of TEXT_EVENT_STREAM.
static MediaType TEXT_HTML
Public constant media type for text/html.
static java.lang.String TEXT_HTML_VALUE
A String equivalent of TEXT_HTML.
static MediaType TEXT_MARKDOWN
Public constant media type for text/markdown.
static java.lang.String TEXT_MARKDOWN_VALUE
A String equivalent of TEXT_MARKDOWN.
static MediaType TEXT_PLAIN
Public constant media type for text/plain.
static java.lang.String TEXT_PLAIN_VALUE
A String equivalent of TEXT_PLAIN.
static MediaType TEXT_XML
Public constant media type for text/xml.
static java.lang.String TEXT_XML_VALUE
A String equivalent of TEXT_XML.也可以直接使用字符串：
@RequestMapping(value = "/test", produces = "application/json;charset=UTF-8",method = {RequestMethod.GET,RequestMethod.POST})