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。
例如web浏览器就是通过MIME类型来判断文件是GIF图片。通过MIME类型来处理json字符串。
Tomcat的安装目录\conf\web.xml 中就定义了大量MIME类型 ，可以参考。
response.setContentType("text/html; charset=utf-8"); html
.setContentType("text/plain; charset=utf-8"); 文本
text/javascript json数据
application/xml xml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。给出的内容类型可以包括字符编码说明，例如：text/html;charset=UTF-8.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");
response.setContentType()的String参数及对应类型
<option value="image/bmp">BMP</option>
<option value="image/gif">GIF</option>
<option value="image/jpeg">JPEG</option>
<option value="image/tiff">TIFF</option>
<option value="image/x-dcx">DCX</option>
<option value="image/x-pcx">PCX</option>
<option value="text/html">HTML</option>
<option value="text/plain">TXT</option>
<option value="text/xml">XML</option>
<option value="application/afp">AFP</option>
<option value="application/pdf">PDF</option>
<option value="application/rtf">RTF</option>
<option value="application/msword">MSWORD</option>
<option value="application/vnd.ms-excel">MSEXCEL</option>
<option value="application/vnd.ms-powerpoint">MSPOWERPOINT</option>
<option value="application/wordperfect5.1">WORDPERFECT</option>
<option value="application/vnd.lotus-wordpro">WORDPRO</option>
<option value="application/vnd.visio">VISIO</option>
<option value="application/vnd.framemaker">FRAMEMAKER</option>
<option value="application/vnd.lotus-1-2-3">LOTUS123</option>
MIME映射策略就是在网页中使用哪个应用程序（即插件），打开哪种文件。另外还有使用权限问题。比如对PDF文档，用“application/pdf “策略。这在动态网页中很常见。出现这种现象，有两种情形：一是使用一个应用程序去打开它不能打开的文档，比如用在标签中定义“DWG”文档用 “application/pdf ”，就会出现无法打开的问题。二是文件扩展名符合要求，但文件内容（格式）不符合要求。你可以检查你浏览的网页源代码，获得出错信息。检查方法是：查看— 源文件。寻找类似于“application/pdf “的字符串，就可以看到，要打开的文件是否与应用程序匹配。 追问 如果不相匹配如何解决回答这通常是由网页编写人来更改。比如：你在源文件里面找到你要打开的文件的HTML标签，在里面加上应用程序即可。比如，你要在网页上打开一个PDF文档，找到PDF文档那一行，在HTML标签里加上 type=“application/pdf “ 就可以了。比如以下HTML文件：
<!----------测试MIME----------->
<html> <head><title>测试MIME</title></head><body> <a type="application/pdf" href="test.pdf">测试MIME</a> </body> </html 将上面的代码保存为test.html，再在相同的位置存储一个pdf文档，双击它就会在网页中打开该文档。
<meta http-equiv="Content-Type" content="text/html; charset=GBK">
response.setContentType() ;
* = application/octet-stream
.001 = application/x-001
.301 = application/x-301
.323 = text/h323
.906 = application/x-906
.907 = drawing/907
.a11 = application/x-a11
.acp = audio/x-mei-aac
.ai = application/postscript
.aif = audio/aiff
.aifc = audio/aiff
.aiff = audio/aiff
.anv = application/x-anv
.asa = text/asa
.asf = video/x-ms-asf
.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
.c4t = application/x-c4t
.c90 = application/x-c90
.cal = application/x-cals
.cat = application/vnd.ms-pki.seccat
.cdf = application/x-netcdf
.cdr = application/x-cdr
.cel = application/x-cel
.cer = application/x-x509-ca-cert
.cg4 = application/x-g4
.cgm = application/x-cgm
.cit = application/x-cit
.class = java/*
.cml = text/xml :客户端浏览器按XML格式进行解析文档
.cmp = application/x-cmp
.cmx = application/x-cmx
.cot = application/x-cot
.crl = application/pkix-crl
.crt = application/x-x509-ca-cert
.csi = application/x-csi
.css = text/css :客户端浏览器按CSS格式进行解析文档
.cut = application/x-cut
.dbf = application/x-dbf
.dbm = application/x-dbm
.dbx = application/x-dbx
.dcd = text/xml :客户端浏览器按XML格式进行解析文档
.dcx = application/x-dcx
.der = application/x-x509-ca-cert
.dgn = application/x-dgn
.dib = application/x-dib
.dll = application/x-msdownload
.doc = application/msword
.dot = application/msword
.drw = application/x-drw
.dtd = text/xml :客户端浏览器按XML格式进行解析文档
.dwf = Model/vnd.dwf
.dwf = application/x-dwf
.dwg = application/x-dwg
.dxb = application/x-dxb
.dxf = application/x-dxf
.edn = application/vnd.adobe.edn
.emf = application/x-emf
.eml = message/rfc822
.ent = text/xml :客户端浏览器按XML格式进行解析文档
.epi = application/x-epi
.eps = application/x-ps
.eps = application/postscript
.etd = application/x-ebx
.exe = application/x-msdownload
.fax = image/fax
.fdf = application/vnd.fdf
.fif = application/fractals
.fo = text/xml :客户端浏览器按XML格式进行解析文档
.frm = application/x-frm
.g4 = application/x-g4
.gbr = application/x-gbr
.gcd = application/x-gcd
.gif = image/gif
.gl2 = application/x-gl2
.gp4 = application/x-gp4
.hgl = application/x-hgl
.hmr = application/x-hmr
.hpg = application/x-hpgl
.hpl = application/x-hpl
.hqx = application/mac-binhex40
.hrf = application/x-hrf
.hta = application/hta
.htc = text/x-component
.htm = text/html :客户端浏览器按超文本格式进行解析文档
.html = text/html :客户端浏览器按超文本格式进行解析文档
.htt = text/webviewhtml
.htx = text/html :客户端浏览器按超文本格式进行解析文档
.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
.isp = application/x-internet-signup
.IVF = video/x-ivf
.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 :客户端浏览器按超文本格式进行解析文档
.la1 = audio/x-liquid-file
.lar = application/x-laplayer-reg
.latex = application/x-latex
.lavs = audio/x-liquid-secure
.lbm = application/x-lbm
.lmsff = audio/x-la-lms
.ls = application/x-javascript
.ltr = application/x-ltr
.m1v = video/x-mpeg
.m2v = video/x-mpeg
.m3u = audio/mpegurl
.m4e = video/mpeg4
.mac = application/x-mac
.man = application/x-troff-man
.math = text/xml
.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
.p7r = application/x-pkcs7-certreqresp
.p7s = application/pkcs7-signature
.pc5 = application/x-pc5
.pci = application/x-pci
.pcl = application/x-pcl
.pcx = application/x-pcx
.pdf = application/pdf :客户端浏览器按PDF格式进行解析文档
.pdf = application/pdf
.pdx = application/vnd.adobe.pdx
.pfx = application/x-pkcs12
.pgl = application/x-pgl
.pic = application/x-pic
.pko = application/vnd.ms-pki.pko
.pl = application/x-perl
.plg = text/html
.pls = audio/scpls
.plt = application/x-plt
.png = image/png
.png = application/x-png
.pot = application/vnd.ms-powerpoint
.ppa = application/vnd.ms-powerpoint
.ppm = application/x-ppm
.pps = application/vnd.ms-powerpoint
.ppt = application/vnd.ms-powerpoint
.ppt = application/x-ppt
.pr = application/x-pr
.prf = application/pics-rules
.prn = application/x-prn
.prt = application/x-prt
.ps = application/x-ps
.ps = application/postscript
.ptn = application/x-ptn
.pwz = application/vnd.ms-powerpoint
.r3t = text/vnd.rn-realtext3d
.ra = audio/vnd.rn-realaudio
.ram = audio/x-pn-realaudio
.ras = application/x-ras
.rat = application/rat-file
.rdf = text/xml
.rec = application/vnd.rn-recording
.red = application/x-red
.rgb = application/x-rgb
.rjs = application/vnd.rn-realsystem-rjs
.rjt = application/vnd.rn-realsystem-rjt
.rlc = application/x-rlc
.rle = application/x-rle
.rm = application/vnd.rn-realmedia
.rmf = application/vnd.adobe.rmf
.rmi = audio/mid
.rmj = application/vnd.rn-realsystem-rmj
.rmm = audio/x-pn-realaudio
.rmp = application/vnd.rn-rn_music_package
.rms = application/vnd.rn-realmedia-secure
.rmvb = application/vnd.rn-realmedia-vbr
.rmx = application/vnd.rn-realsystem-rmx
.rnx = application/vnd.rn-realplayer
.rp = image/vnd.rn-realpix
.rpm = audio/x-pn-realaudio-plugin
.rsml = application/vnd.rn-rsml
.rt = text/vnd.rn-realtext
.rtf = application/msword
.rtf = application/x-rtf
.rv = video/vnd.rn-realvideo
.sam = application/x-sam
.sat = application/x-sat
.sdp = application/sdp
.sdw = application/x-sdw
.sit = application/x-stuffit
.slb = application/x-slb
.sld = application/x-sld
.slk = drawing/x-slk
.smi = application/smil
.smil = application/smil
.smk = application/x-smk
.snd = audio/basic
.sol = text/plain
.sor = text/plain
.spc = application/x-pkcs7-certificates
.spl = application/futuresplash
.spp = text/xml
.ssm = application/streamingmedia
.sst = application/vnd.ms-pki.certstore
.stl = application/vnd.ms-pki.stl
.stm = text/html
.sty = application/x-sty
.svg = text/xml
.swf = application/x-shockwave-flash :客户端浏览器按 Flash 格式进行解析文档
.tdf = application/x-tdf
.tg4 = application/x-tg4
.tga = application/x-tga
.tif = image/tiff
.tif = application/x-tif
.tiff = image/tiff
.tld = text/xml
.top = drawing/x-top
.torrent = application/x-bittorrent
.tsd = text/xml
.txt = text/plain :客户端浏览器按 纯文本 格式进行解析文档
.uin = application/x-icq
.uls = text/iuls
.vcf = text/x-vcard
.vda = application/x-vda
.vdx = application/vnd.visio
.vml = text/xml
.vpg = application/x-vpeg005
.vsd = application/vnd.visio
.vsd = application/x-vsd
.vss = application/vnd.visio
.vst = application/vnd.visio
.vst = application/x-vst
.vsw = application/vnd.visio
.vsx = application/vnd.visio
.vtx = application/vnd.visio
.vxml = text/xml
.wav = audio/wav
.wax = audio/x-ms-wax
.wb1 = application/x-wb1
.wb2 = application/x-wb2
.wb3 = application/x-wb3
.wbmp = image/vnd.wap.wbmp
.wiz = application/msword
.wk3 = application/x-wk3
.wk4 = application/x-wk4
.wkq = application/x-wkq
.wks = application/x-wks
.wm = video/x-ms-wm
.wma = audio/x-ms-wma
.wmd = application/x-ms-wmd
.wmf = application/x-wmf
.wml = text/vnd.wap.wml
.wmv = video/x-ms-wmv
.wmx = video/x-ms-wmx
.wmz = application/x-ms-wmz
.wp6 = application/x-wp6
.wpd = application/x-wpd
.wpg = application/x-wpg
.wpl = application/vnd.ms-wpl
.wq1 = application/x-wq1
.wr1 = application/x-wr1
.wri = application/x-wri
.wrk = application/x-wrk
.ws = application/x-ws
.ws2 = application/x-ws
.wsc = text/scriptlet
.wsdl = text/xml
.wvx = video/x-ms-wvx
.xdp = application/vnd.adobe.xdp
.xdr = text/xml
.xfd = application/vnd.adobe.xfd
.xfdf = application/vnd.adobe.xfdf
.xhtml = text/html
.xls = application/vnd.ms-excel
.xls = application/x-xls
.xlw = application/x-xlw
.xml = text/xml
.xpl = audio/scpls
.xq = text/xml
.xql = text/xml
.xquery = text/xml
.xsd = text/xml
.xsl = text/xml
.xslt = text/xml
.xwd = application/x-xwd
.x_b = application/x-x_b
.x_t = application/x-x_t