一、contentType的作用
Content-Type来表示报文主体的媒体类型。
如CSDN某个请求，表示答复的信息为json数据。
二、常见类型
text/html ： HTML格式 application/x-www-form-urlencoded form表单数据被编码 application/json ： JSON数据格式 text/plain ：纯文本格式 text/xml ： XML格式 image/gif ：gif图片格式 image/jpeg ：jpg图片格式 image/png：png图片格式 application/octet-stream ： 二进制流数据
参考
| 文件扩展名 | Content-Type(Mime-Type) | 文件扩展名 | Content-Type(Mime-Type) |
| .* | application/octet-stream | .tif | image/tiff |
| .asp | text/asp | .asx | video/x-ms-asf |
| .au | audio/basic | .avi | video/avi |
| .awf | application/vnd.adobe.workflow | .biz | text/xml |
| .bmp | application/x-bmp | .bot | application/x-bot |
| .cit | application/x-cit | .class | java/* |
| .csi | application/x-csi | .css | text/css |
| .dcd | text/xml | .dcx | application/x-dcx |
| .dib | application/x-dib | .dll | application/x-msdownload |
| .doc | application/msword | .dot | application/msword |
| .drw | application/x-drw | .dtd | text/xml |
| .dwf | Model/vnd.dwf | .dwf | application/x-dwf |
| .etd | application/x-ebx | .exe | application/x-msdownload |
| .gif | image/gif | .gl2 | application/x-gl2 |
| .hrf | application/x-hrf | .hta | application/hta |
| .htc | text/x-component | .htm | text/html |
| .html | text/html | .htt | text/webviewhtml |
| .htx | text/html | .icb | application/x-icb |
| .ico | image/x-icon | .ico | application/x-ico |
| .iff | application/x-iff | .ig4 | application/x-g4 |
| .igs | application/x-igs | .iii | application/x-iphone |
| .img | application/x-img | .ins | application/x-internet-signup |
| .java | java/* | .jfif | image/jpeg |
| .jpe | image/jpeg | .jpe | application/x-jpe |
| .jpeg | image/jpeg | .jpg | image/jpeg |
| .jpg | application/x-jpg | .js | application/x-javascript |
| .jsp | text/html | .la1 | audio/x-liquid-file |
| .mdb | application/msaccess | .mdb | application/x-mdb |
| .mfp | application/x-shockwave-flash | .mht | message/rfc822 |
| .mhtml | message/rfc822 | .mi | application/x-mi |
| .mid | audio/mid | .midi | audio/mid |
| .mil | application/x-mil | .mml | text/xml |
| .mnd | audio/x-musicnet-download | .mns | audio/x-musicnet-stream |
| .mocha | application/x-javascript | .movie | video/x-sgi-movie |
| .mp1 | audio/mp1 | .mp2 | audio/mp2 |
| .mp2v | video/mpeg | .mp3 | audio/mp3 |
| .mp4 | video/mpeg4 | .mpa | video/x-mpg |
| .mpd | application/vnd.ms-project | .mpe | video/x-mpeg |
| .mpeg | video/mpg | .mpg | video/mpg |
| .mpga | audio/rn-mpeg | .mpp | application/vnd.ms-project |
| .mps | video/x-mpeg | .mpt | application/vnd.ms-project |
| .mpv | video/mpg | .mpv2 | video/mpeg |
| .mpw | application/vnd.ms-project | .mpx | application/vnd.ms-project |
| .mtx | text/xml | .mxp | application/x-mmxp |
| .net | image/pnetvue | .nrf | application/x-nrf |
| .nws | message/rfc822 | .odc | text/x-ms-odc |
| .out | application/x-out | .p10 | application/pkcs10 |
| .p12 | application/x-pkcs12 | .p7b | application/x-pkcs7-certificates |
| .p7c | application/pkcs7-mime | .p7m | application/pkcs7-mime |
