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

Question

我遇到了这个异常的问题：

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 行出了什么问题。

显然是这样称呼的： com.controlj.green.definitions.Utilities.getBackground();

这是：

    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？

谢谢。

Answer 1

从堆栈跟踪，

根本原因 javax.servlet.ServletException： java.lang.IncompatibleClassChangeError: 找到类
com.mysql.jdbc.Statement，但需要接口

你为什么要在这里投statement类，

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

需要，

Statement st =con.createStatement();

期望con 成为连接对象

更新：

根据您分享的错误导入，

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;

希望对你有帮助

Answer 2

什么是骗局 Statement st = (Statement) con.createStatement();
是从哪里来的。无论如何，您不需要对 Statement 进行强制转换。

Answer 3

您从哪里获得连接？全局变量？，我会尝试将您准备好的语句更改为类似的内容。我不知道您是否在某些时候控制异常以顺便关闭连接。

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("");
   }
}

Answer 4

我认为我们不需要像你在这里所做的那样进行铸造

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一些旧版本的 mysql-connector.jar 尝试用一些 newer version 替换它并再次导入连接语句