连接池并发问题！

java.sql.SQLException: We are already in the process of making 21 connections and the number of simultaneous builds has been throttled to 20
at org.logicalcobwebs.proxool.Prototyper.checkSimultaneousBuildThrottle(Prototyper.java:260)
at org.logicalcobwebs.proxool.ConnectionPool.getConnection(ConnectionPool.java:164)
at org.logicalcobwebs.proxool.ProxoolDriver.connect(ProxoolDriver.java:89)
at java.sql.DriverManager.getConnection(DriverManager.java:582)
at java.sql.DriverManager.getConnection(DriverManager.java:207)
at database.BasicDAO.initConnection(BasicDAO.java:29)
at database.BasicDAO.<init>(BasicDAO.java:41)
at mobile.DemoMobile.doPost(DemoMobile.java:51)
at mobile.DemoMobile.doGet(DemoMobile.java:32)
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:859)
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(Thread.java:619)