还原问题:

  request.setCharacterEncoding("UTF-8");
  response.setContentType("text/html;charset=UTF-8");
  request.setCharacterEncoding("UTF-8");

  response.getOutputStream().println("中文");

java.io.CharConversionException: Not an ISO 8859-1 character: 中
 at javax.servlet.ServletOutputStream.print(ServletOutputStream.java:89)
 at javax.servlet.ServletOutputStream.println(ServletOutputStream.java:242)
 at com.zwly.server.TanksServlet.doPost(TanksServlet.java:71)
 at com.zwly.server.TanksServlet.doGet(TanksServlet.java:24)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
 at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852)
 at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
 at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
 at java.lang.Thread.run(Unknown Source)

解决：

   PrintWriter out = response.getWriter();   out.print("中文");