Question

我遇到这个例外的问题：

type Exception report

message An exception occurred processing JSP page /home/index.jsp at line 54

description The server encountered an internal error that prevented it from fulfilling this   request.

exception

org.apache.jasper.JasperException: An exception occurred processing JSP page /home/index.jsp at line 54

51:     <link rel="shortcut icon" href="../assets/ico/favicon.png"> 
52:     <style type="text/css"> 
53:     <%  
54:         HashMap<String,Object> background = com.controlj.green.definitions.Utilities.getBackground();
55:             String background_image = "";
56:             if(!background.isEmpty()){
57:                 background_image = "data:image/png;base64," + background.get("bytes").toString();


Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:568)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:455)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
com.controlj.green.servlets.Index.doGet(Index.java:51)
javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

root cause

javax.servlet.ServletException: java.lang.IncompatibleClassChangeError: Found class   com.mysql.jdbc.Statement, but interface was expected
 org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:912)
 org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:841)
 org.apache.jsp.home.index_jsp._jspService(index_jsp.java:83)
 org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
 org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
 org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
 org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
 com.controlj.green.servlets.Index.doGet(Index.java:51)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

 root cause

 java.lang.IncompatibleClassChangeError: Found class com.mysql.jdbc.Statement, but interface was expected
 com.controlj.green.definitions.Utilities.getBackground(Utilities.java:172)    org.apache.jsp.home.index_jsp._jspService(index_jsp.java:68)
 org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
 org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
 org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
 org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
 com.controlj.green.servlets.Index.doGet(Index.java:51)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
 javax.servlet.http.HttpServlet.service(HttpServlet.java:728)

 note The full stack trace of the root cause is available in the Apache Tomcat/7.0.42 logs.
 Apache Tomcat/7.0.42

我真的不知道第54行的错误。

显然这称之为： com.controlj.green.definitions.Utilities.getBackground（）;

是：

    import java.util.*;

    public static HashMap<String,Object> getBackground() throws SQLException, ClassNotFoundException, IOException {
    if(establishConnection()){

        Statement st = (Statement) con.createStatement();
        rs = st.executeQuery("select bytes from connection_string");

        ResultSetMetaData md = (ResultSetMetaData) rs.getMetaData();
        int columns = md.getColumnCount();
        HashMap<String,Object> list = new HashMap<String,Object>();

        if (rs.next()) {
            for(int i=1; i<=columns; ++i){
                list.put(md.getColumnName(i),rs.getObject(i));
                }
            }    
        return list;
    }else{
        return null;
    }

}

这可能有什么问题？

感谢。

Answer 1

来自堆栈跟踪，

根本原因javax.servlet.ServletException：   java.lang.IncompatibleClassChangeError：找到类
  com.mysql.jdbc.Statement，但预期接口

为什么要在这里投射statement课程，

Statement st = (Statement) con.createStatement();

它必须是，

Statement st =con.createStatement();

期望con成为连接对象

<强>更新

根据您分享错误导入的错误，

错误的课程

import com.mysql.jdbc.Connection;
import com.mysql.jdbc.Statement;

应该是

import java.sql.Connection;
import java.sql.Statement;

希望这有帮助

Answer 2

什么是骗局 Statement st = (Statement) con.createStatement();
来自哪里。无论如何，你不需要演员声明。

Answer 3

我认为我们不需要像你在这里那样进行投射

Statement st = (Statement) con.createStatement();

只要con是java.sql.Connection

类型的对象

或者您可能正在使用某些旧版mysql-connector.jar尝试将其替换为某些newer version并再次导入连接语句

Answer 4

你从哪里获得连接？全局变量？，我会尝试更改你准备好的语句，就像这样。我不知道你是否在某种程度上控制了异常以便顺便关闭连接。

PreparedStatement ps = null;

try{
    ps = conn.prepareStatement("select bytes from connection_string");
    ps.executeQuery();
} catch(Exception ex){
    System.out.println("");
} finally {
   try{
       if(ps!=null){
           ps.close();
       }
       if(conn!=null){
           conn.close();
       }
   } catch(Exception ex){
       System.out.println("");
   }
}

HTTP状态500 - 在第54行处理JSP页面/home/index.jsp时发生异常

4 个答案: