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

Question

嗨，当我尝试用我的Java示例代码连接oracle时，我是Java新手，但出现了以上异常

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();
    }
    }

}

并且抛出的异常是

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)

帮我解决一下

Answer 1

首先，连接URL错误。8080后通常由Web服务器（如Apache Tomcat）使用。Oracle本身使用默认端口1521。另请参见此Oracle
JDBC文档
。

再者，你忘了打电话ResultSet#next()。这会将光标设置到结果集中的下一行。结果集将与游标一起返回到第一行
之前 。如果您不移动光标，则getXXX()对的任何调用ResultSet都会失败。

如果您期望结果集中有多行，则需要使用while循环：

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

或者，如果只希望一行，那么您还可以继续执行以下if语句：

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（同样在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发生资源泄漏。在GET请求上加载JDBC驱动程序也不必要地昂贵。在应用程序启动或servlet初始化期间只需执行一次。