关于oracle的java.sql.SQLException，ORA-12519。
最近我弄的一个程序，老是报错。内容如下：
java.sql.SQLException: Listener refused the connection with the following error:
ORA-12519, TNS:no appropriate service handler found
The Connection descriptor used by the client was:
localhost:1521:orcl
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:145)
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:380)
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:401)
at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:441)
at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:165)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:35)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:839)
at java.sql.DriverManager.getConnection(DriverManager.java:579)
at java.sql.DriverManager.getConnection(DriverManager.java:221)
at com.wyc.util.RecursionTest.dbConn(RecursionTest.java:221)
at com.wyc.util.RecursionTest.GetResultSet(RecursionTest.java:185)
at com.wyc.util.RecursionTest.GetElementNum(RecursionTest.java:195)
at org.apache.jsp.LoadDbTable.test_jsp._jspService(test_jsp.java:293)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:393)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
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:230)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:722)

这是怎么回事？


------解决方案--------------------
http://blog.csdn.net/diguoguo/article/details/6185536
------解决方案--------------------
有时候连得上数据库,有时候又连不上.

可能是数据库上当前的连接数目已经超过了它能够处理的最大值.


select count(*) from v$process --当前的连接数
select value from v$parameter where name = 'processes' --数据库允许的最大连接数
修改最大连接数:
alter system set processes = 300 scope = spfile;
重启数据库:
shutdown immediate;
startup;
--查看当前有哪些用户正在使用数据
SELECT osuser, a.username,cpu_time/executions/1000000
------解决方案--------------------
's', sql_fulltext,machine