java.sql.SQLException:Io异常:在与oracle的JDBC连接期间从读取调用中减去了一个

Question

嗨,当我尝试使用我的java示例代码连接oracle时,我是java的新手,我得到了上述异常

我的代码是

import java.sql.*;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class DbConnectivity extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
    {
       try {
        Class.forName("oracle.jdbc.driver.OracleDriver");
        Connection con = DriverManager.getConnection("jdbc:oracle:thin:@localhost:8080:orcl", "system", "tiger");\\ The Exception thrown here
        Statement stmt = con.createStatement();
        ResultSet rst = stmt.executeQuery("select * from users");
        System.out.println(rst.getString(1));
        stmt.close();
        con.close();
    } catch (ClassNotFoundException e) 
    {
        e.printStackTrace();
    } catch (SQLException e) 
    {
        e.printStackTrace();
    }
    }

}

抛出的异常是

java.sql.SQLException: Io exception: Got minus one from a read call
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:112)
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:146)
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:255)
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:387)
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:801)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at com.wipro.connnection.DbConnectivity.doGet(DbConnectivity.java:16)
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.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Unknown Source)

帮我理清一下

Answer 1

首先,连接URL是错误的.Post 8080通常由Apache Tomcat等Web服务器使用.Oracle本身使用默认端口1521.另请参阅此Oracle JDBC文档.

你忘了打电话了ResultSet#next().这会将光标设置为结果集中的下一行.返回结果集,光标位于第一行之前.如果不移动光标,任何getXXX()对该调用的调用ResultSet都将失败.

如果您希望结果集中有多行,则需要使用while循环:

resultSet = statement.executeQuery();
while (resultSet.next()) {
    String columnname = resultSet.getString("columnname");
    // ...
}

或者,如果您只期望一行,那么您也可以继续if声明:

resultSet = statement.executeQuery();
if (resultSet.next()) {
    String columnname = resultSet.getString("columnname");
    // ...
}

有关正确使用基本 JDBC的更多提示和示例(也在JSP/Servlet中),您可能会发现本文很有用.例如,关闭语句和连接的方式容易导致资源泄漏.在GET请求上加载JDBC驱动程序也是非常昂贵的.只需在应用程序启动或servlet初始化期间执行一次.