作用
Response.setContentType(MIME)的作用是使客户端浏览器，区分不同种类的数据，并根据不同的MIME调用浏览器内不同的程序嵌入模块来处理相应的数据。这个方法设置发送到客户端的响应的内容类型，此时响应还没有提交。给出的内容类型定义中还可以包括字符编码说明，例如：text/html; charset=UTF-8。
该方法的设置顺序对其设置效果有不同影响，如果该方法在getWriter()方法被调用之前调用，那么响应的字符编码将仅从给出的内容类型中设置。该方法如果在getWriter()方法被调用之后或者在被提交之后调用，将不会设置响应的字符编码。在使用http协议的情况中，该方法将会设置 Content-type实体报头。
一般在Servlet中，习惯性的会首先设置请求以及响应的内容类型以及编码方式：
response.setContentType("text/html; charset=UTF-8");request.setCharacterEncoding("UTF-8"); Tomcat的安装目录\conf\web.xml 中定义了大量MIME类型 ，可以参考。
返回文件类型与对应值
3gp video/3gpp 7z application/x-7z-compressed air application/vnd.adobe.air-application-installer-package+zip apk application/vnd.android.package-archive application application/x-ms-application apr application/vnd.lotus-approach asc application/pgp-signature asm text/x-asm atom application/atom+xml atomcat application/atomcat+xml avi video/x-msvideo bat application/x-msdownload bdm application/vnd.syncml.dm+wbxml bin application/octet-stream bmp image/bmp body text/html book application/vnd.framemaker box application/vnd.previewsystems.box c text/x-c car application/vnd.curl.car cat application/vnd.ms-pki.seccat cdkey application/vnd.mediastation.cdkey chm application/vnd.ms-htmlhelp class application/java cmc application/vnd.cosmocaller com application/x-msdownload conf text/plain crt application/x-x509-ca-cert csv text/csv dataless application/vnd.fdsn.seed def text/plain deploy application/octet-stream dir application/x-director dis application/vnd.mobius.dis dist application/octet-stream distz application/octet-stream djv image/vnd.djvu djvu image/vnd.djvu dll application/x-msdownload dmg application/x-apple-diskimage dmp application/vnd.tcpdump.pcap dms application/octet-stream dna application/vnd.dna doc application/msword docx application/vnd.openxmlformats-officedocument.wordprocessingml.document dot application/msword dotm application/vnd.ms-word.template.macroenabled.12 dotx application/vnd.openxmlformats-officedocument.wordprocessingml.template dp application/vnd.osgi.dp dump application/octet-stream dwf model/vnd.dwf dwg image/vnd.dwg eot application/vnd.ms-fontobject exe application/octet-stream ext application/vnd.novadigm.ext gif image/gif gqs application/vnd.grafeq gz application/x-gzip h text/x-c htm text/html html text/html ico image/x-icon imp application/vnd.accpac.simply.imp install application/x-install-instructions iso application/x-iso9660-image jam application/vnd.jam jar application/java-archive java text/x-java-source joda application/vnd.joost.joda-archive jpe image/jpeg jpeg image/jpeg jpg image/jpeg jpgm video/jpm jpgv video/jpeg jpm video/jpm js application/javascript jsf text/plain json application/json jsonml application/jsonml+json jspf text/plain list text/plain mac image/x-macpaint man text/troff mdb application/x-msaccess movie video/x-sgi-movie mp1 audio/mpeg mp2 audio/mpeg mp21 application/mp21 mp2a audio/mpeg mp3 audio/mpeg mp4 video/mp4 mp4a audio/mp4 mp4s application/mp4 mp4v video/mp4 mpeg video/mpeg mpega audio/x-mpeg mpg video/mpeg mpg4 video/mp4 mpn application/vnd.mophun.application obd application/x-msbinder obj application/x-tgif oth application/vnd.oasis.opendocument.text-web pbm image/x-portable-bitmap pdb application/vnd.palm application/pdf ppsx application/vnd.openxmlformats-officedocument.presentationml.slideshow ppt application/vnd.ms-powerpoint pptm application/vnd.ms-powerpoint.presentation.macroenabled.12 pptx application/vnd.openxmlformats-officedocument.presentationml.presentation pub application/x-mspublisher rm application/vnd.rn-realmedia rmi audio/midi scm application/vnd.lotus-screencam sh application/x-sh sub text/vnd.dvb.subtitle text text/plain wmv video/x-ms-wmv wmx video/x-ms-wmx wmz application/x-msmetafile woff application/x-font-woff wpd application/vnd.wordperfect xlm application/vnd.ms-excel xlsx application/vnd.openxmlformats-officedocument.spreadsheetml.sheet xml application/xml yin application/yin+xml z application/x-compress Z application/x-compress z1 application/x-zmachine z2 application/x-zmachine z3 application/x-zmachine z4 application/x-zmachine z5 application/x-zmachine z6 application/x-zmachine z7 application/x-zmachine z8 application/x-zmachine zaz application/vnd.zzazz.deck+xml zip application/zip zir application/vnd.zul zirz application/vnd.zul zmm application/vnd.handheld-entertainment+xml