java - MYSQL连接关闭后不允许操作

Question

基本上我有:

String query = "SELECT * FROM table WHERE UNIQUEID=? AND DIR IS NOT NULL AND NAME IS NOT NULL AND PAGETYPE IS NOT NULL";
DBConnect Database = new DBConnect();
Connection con = null;
PreparedStatement ps = null;
ResultSet rs=null;
try {
    con = Database.getcon();
    ps = con.prepareStatement(query);
    ps.setString(1, URI);
    rs=ps.executeQuery();
    if(rs.next()){
    }
} finally {
    if(ps != null)
        ps.close();
    if(rs != null)
        rs.close();
    if(con != null)
        con.close();
}
query = "SELECT COUNTCOMMENTS FROM videosinfos WHERE UNIQUEID=?";
try {
    con = Database.getcon();
    ps = con.prepareStatement(query); // Getting error here
    rs=ps.executeQuery();
    ps.setString(1, URI);
    rs=ps.executeQuery();
    if(rs.next()){
        comments = rs.getInt(1);
    }
} finally {
    if(ps != null)
        ps.close();
    if(rs != null)
        rs.close();
    if(con != null)
        con.close();
}

注意:我得到错误的那一行，对其进行评论。

连接到数据库:

public DBConnect(){
    try{
        Class.forName("com.mysql.jdbc.Driver");

        String unicode="useSSL=false&autoReconnect=true&useUnicode=yes&characterEncoding=UTF-8";
        con = DriverManager.getConnection("jdbc:mysql://localhost:15501/duckdb?"+unicode, "root", "_PWD");
        st = con.createStatement();
    }catch(Exception ex){
        System.out.println(ex.getMessage());
        System.out.println("couldn't connect!");
    }
}
public Connection getcon(){
    DBConnect condb = new DBConnect();
    Connection connect = con;
    return con;
}

但是在编译时我得到这个错误:

com.mysql.jdbc.exceptions.jdbc4.MySQLNonTransientConnectionException: No operations allowed after connection closed. at sun.reflect.GeneratedConstructorAccessor18.newInstance(Unknown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at com.mysql.jdbc.Util.handleNewInstance(Util.java:404) at com.mysql.jdbc.Util.getInstance(Util.java:387) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:917) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:896) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:885) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:860) at com.mysql.jdbc.ConnectionImpl.throwConnectionClosedException(ConnectionImpl.java:1246) at com.mysql.jdbc.ConnectionImpl.checkClosed(ConnectionImpl.java:1241) at com.mysql.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:4102) at com.mysql.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:4071) at duck.reg.pack.DBConnect.getitemfull_details(DBConnect.java:686) at duck.reg.pack.index.doPost(index.java:73) at javax.servlet.http.HttpServlet.service(HttpServlet.java:661) at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:80) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:799) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1455) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:748)

我将 Debian 与 MariaDB v10.x/Mysql 结合使用

Answer 1

有两个原因:

• 连接在第一个 PreparedStatement 执行后关闭
• getcon 使用 instance 变量而不是 local 变量。因此，下次调用 getcon 时，会返回相同的 conn 变量(之前关闭的变量)。

要解决此问题，需要修改 getcon 和 DBConnect 以声明一个本地 conn 变量并返回它(事实上，您不需要根本不需要 DBConnect)，例如:

public Connection getcon(){
    try{
        Class.forName("com.mysql.jdbc.Driver");
        String unicode="useSSL=false&autoReconnect=true&useUnicode=yes&characterEncoding=UTF-8";
        return DriverManager.getConnection("jdbc:mysql://localhost:15501/duckdb?"+unicode, "root", "_PWD");
    }catch(Exception ex){
        System.out.println(ex.getMessage());
        System.out.println("couldn't connect!");
        throw new RuntimeException(ex);
    }
}