请求流程：
1、访问SearchList.jsp时请求servlet：SearchById;
2、SearchById 的doPost方法访问showInfoDao.findModeResult(sql);
3、JdbcUtils中对sql进行数据库查询，并将查询结果返回，展示在SearchList.jsp页面；
在第3步，数据库连接成功，查询的时候出现了“com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax;”
报错信息如下：
doGet 请求
doPost请求
数据库连接成功！
com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from??personinfo' at line 1
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.Util.getInstance(Util.java:381)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1030)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3515)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3447)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1951)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2101)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2554)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1761)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:1912)
at com.bdwm.dao.ShowInfoDao.findModeResult(ShowInfoDao.java:18)
at com.bdwm.servlet.SearchById.doPost(SearchById.java:71)
at com.bdwm.servlet.SearchById.doGet(SearchById.java:49)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:169)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:956)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:436)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1078)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:625)
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2517)
at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2506)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
[]
check the manual that corresponds to your MySQL server version for the right syntax to use near 'from??personinfo' at line 1
这不提示很明显，是sql有问题吗， from和personinfo中间两个??，看看是不是编码有问题了
把那个sql拷贝出来，在记事本中粘贴一下，然后再从记事本中拷贝到代码中试试
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'from??personinfo' at line 1
这是异常是因为SQL语句出错了。错误提示里面说：“from??personinfo”这个位置附近出错了。你注意两点：第一，看看SQL语句里面表的名称有没有输入错误；第二，如果是用字符串拼接的SQL语句，一定要注意两个字符串之间的
”空格“（比如sql1=“select * from student”; sql2="where id = 3"; sql = sql1 +sql2, 最终的sql语句就成了sql= "select * from studentwhere id = 3"。此时，student和where就成了一个单词，导致sql语句出错。因此，在拼接时给sql1最后，或者sql2之前加一个空格就好了，例如sql2="where id = 3"; sql = sql1 +sql2, 最终的sql语句就成了sql= "空格符select * from studentwhere id = 3")。
希望能够帮到你！
SQL语句写的不对。断点调试。取到SQL语句的内容，放到mysql数据库验证下语句是否能正确执行。如果能正确执行，但在代码中报错，可以试着在语句末尾加空格或去掉别名。
把SQL语句发出来，看下啊
错误提示很明显的说：你的sql语法错吴，把sql贴错来看看。