Java:结果集错误-6ren

Java:结果集错误

转载作者：行者123 更新时间：2023-11-30 04:03:29

    String temp[]=bookName.split(" ");
    ArrayList list=new ArrayList();

    try {
        con=ds.getConnection(); 
        pst=con.prepareStatement("select distinct book_name from booksinventory");
        rs=pst.executeQuery();

        for(int i=0;i<temp.length;i++)
        {
            while(rs.next())
            {
                //System.out.println(rs.getString(1)+" contains "+temp[i]);
                line no 631 --> System.out.println(rs.getString(1)+" contains "+temp[i]+":"+(rs.getString(1).toUpperCase()).contains(temp[i].toUpperCase()));
                if((rs.getString(1).toUpperCase()).contains(temp[i].toUpperCase()))
                {
                    list.add(rs.getString(1));
                    System.out.println(list);
                }
            }
            rs.beforeFirst();
        }
        System.out.println(list);
        Set<String> set=new HashSet<String>();
        set.addAll(list);
        list.removeAll(list);
        list.addAll(set);
        list.removeAll(Collections.singleton(null));

        con.close();
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    return list;

在这里，我尝试搜索我的记录以检查记录中是否存在一组特定的关键字。我尝试了几乎所有方法都无法找出错误..我认为它与语句“rs.beforeFirst()”有关，因为它只打印第一次迭代..以下来自控制台..

    16:55:06,240 INFO  [STDOUT] Let us C contains let:true
    16:55:06,240 INFO  [STDOUT] [Let us C]
    16:55:06,240 INFO  [STDOUT] Let us C++ contains let:true
    16:55:06,240 INFO  [STDOUT] [Let us C, Let us C++]
    16:55:06,240 INFO  [STDOUT] Let us HTML contains let:true
    16:55:06,240 INFO  [STDOUT] [Let us C, Let us C++, Let us HTML]
    16:55:06,240 INFO  [STDOUT] dfgdfg contains let:false
    16:55:06,240 INFO  [STDOUT] digital electronics contains let:false
    16:55:06,240 INFO  [STDOUT] java contains let:false
    16:55:06,241 INFO  [STDOUT] oops contains let:false
    16:55:06,241 INFO  [STDOUT] quantum computing contains let:false
    16:55:06,241 INFO  [STDOUT] sdf contains let:false
    16:55:06,241 ERROR [[SearchBooksCombo]] Servlet.service() for servlet SearchBooksCombo threw exception
    java.lang.NullPointerException
        at com.classes.dao.LibraryDAO.getMatchingBooks(LibraryDAO.java:631)
        at com.classes.servlets.SearchBooksCombo.doGet(SearchBooksCombo.java:37)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
        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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654)
        at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:557)
        at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:481)
        at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:968)
        at org.apache.jsp.addCopy_jsp._jspService(addCopy_jsp.java:80)
        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:373)
        at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:336)
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
        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.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
        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.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:182)
        at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
        at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
        at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446)
        at java.lang.Thread.run(Unknown Source)
    16:55:06,241 ERROR [[jsp]] Servlet.service() for servlet jsp threw exception
    java.lang.NullPointerException
        at com.classes.dao.LibraryDAO.getMatchingBooks(LibraryDAO.java:631)
        at com.classes.servlets.SearchBooksCombo.doGet(SearchBooksCombo.java:37)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
        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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654)
        at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:557)
        at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:481)
        at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:968)
        at org.apache.jsp.addCopy_jsp._jspService(addCopy_jsp.java:80)
        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:373)
        at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:336)
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
        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.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
        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.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:182)
        at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
        at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
        at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446)
        at java.lang.Thread.run(Unknown Source)
    16:55:06,242 INFO  [CachedConnectionManager] Closing a connection for you.  Please close them yourself: org.jboss.resource.adapter.jdbc.jdk5.WrappedConnectionJDK5@52fdeb
    java.lang.Throwable: STACKTRACE
        at org.jboss.resource.connectionmanager.CachedConnectionManager.registerConnection(CachedConnectionManager.java:290)
        at org.jboss.resource.connectionmanager.BaseConnectionManager2.allocateConnection(BaseConnectionManager2.java:423)
        at org.jboss.resource.connectionmanager.BaseConnectionManager2$ConnectionManagerProxy.allocateConnection(BaseConnectionManager2.java:849)
        at org.jboss.resource.adapter.jdbc.WrapperDataSource.getConnection(WrapperDataSource.java:89)
        at com.classes.dao.LibraryDAO.getMatchingBooks(LibraryDAO.java:622)
        at com.classes.servlets.SearchBooksCombo.doGet(SearchBooksCombo.java:37)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:690)
        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.ApplicationDispatcher.invoke(ApplicationDispatcher.java:654)
        at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:557)
        at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:481)
        at org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:968)
        at org.apache.jsp.addCopy_jsp._jspService(addCopy_jsp.java:80)
        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:373)
        at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:336)
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
        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.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
        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.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:182)
        at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:84)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
        at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:157)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:262)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
        at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:446)
        at java.lang.Thread.run(Unknown Source)

最佳答案

"because it is only printing for the first iteration."

来自ResultSet javadoc 。

A default ResultSet object is not updatable and has a cursor that moves forward only. Thus, you can iterate through it only once and only from the first row to the last row. It is possible to produce ResultSet objects that are scrollable and/or updatable. The following code fragment, in which con is a valid Connection object, illustrates how to make a result set that is scrollable and insensitive to updates by others, and that is updatable. See ResultSet fields for other options.

   Statement stmt = con.createStatement(
                                  ResultSet.TYPE_SCROLL_INSENSITIVE,
                                  ResultSet.CONCUR_UPDATABLE);
   ResultSet rs = stmt.executeQuery("SELECT a, b FROM TABLE2");
   // rs will be scrollable, will not show changes made by others,
   // and will be updatable

关于Java:结果集错误，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/21380043/

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Java:结果集错误