數據庫輪詢：MySQLNonTransientConnectionException：太多的連接

Question

我已經寫了一個WebService負責輪詢數據庫每3秒和發送的最新數據

不幸的是我得到這個例外在我的控制檯一段時間後。

Connection Failed! Check output console 
com.mysql.jdbc.exceptions.MySQLNonTransientConnectionException: Too many connections 
     at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:921) 
     at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:2985) 
     at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:885) 
     at com.mysql.jdbc.MysqlIO.secureAuth411(MysqlIO.java:3421) 
     at com.mysql.jdbc.MysqlIO.doHandshake(MysqlIO.java:1247) 
     at com.mysql.jdbc.Connection.createNewIO(Connection.java:2775) 
     at com.mysql.jdbc.Connection.<init>(Connection.java:1555) 
     at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:285) 
     at java.sql.DriverManager.getConnection(DriverManager.java:579) 
     at java.sql.DriverManager.getConnection(DriverManager.java:221) 
     at com.serviceees.DBPollerService.getUpdates(DBPollerService.java:47) 
     at sun.reflect.GeneratedMethodAccessor51.invoke(Unknown Source) 
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 
     at java.lang.reflect.Method.invoke(Method.java:601) 
     at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$TypeOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:168) 
     at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:70) 
     at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:279) 
     at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:86) 
     at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:136) 
     at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:74) 
     at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1357) 
     at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1289) 
     at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1239) 
     at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1229) 
     at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:420) 
     at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:497) 
     at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:684) 
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) 
     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:291) 
     at org.apache.coyote.http11.Http11AprProcessor.process(Http11AprProcessor.java:877) 
     at org.apache.coyote.http11.Http11AprProtocol$Http11ConnectionHandler.process(Http11AprProtocol.java:594) 
     at org.apache.tomcat.util.net.AprEndpoint$Worker.run(AprEndpoint.java:1675) 
     at java.lang.Thread.run(Thread.java:722) 

這是我的計劃

package com.serviceees; 


import java.sql.Connection; 
import java.sql.DriverManager; 
import java.sql.PreparedStatement; 
import java.sql.ResultSet; 
import java.sql.SQLException; 
import java.util.ArrayList; 

import javax.ws.rs.GET; 
import javax.ws.rs.Path; 
import javax.ws.rs.Produces; 

import com.google.gson.Gson; 

import dto.Orders; 

@Path("/updates") 
public class DBPollerService { 
    @GET 
    @Produces("application/json") 
    public String getUpdates() { 
     String clientResponse = "Error"; 
     ArrayList<Orders> newOrdersList = new ArrayList<Orders>(); 
     Gson gson = new Gson(); 
     try { 

      try { 
       Class.forName("com.mysql.jdbc.Driver"); 
      } catch (ClassNotFoundException e) { 
       e.printStackTrace(); 
      } 
      Connection connection = null; 
      PreparedStatement preparedStatement = null; 
      String selectSQL = "SELECT *\r\n" + 
      "FROM Orders\r\n" + 
      "INNER JOIN (\r\n" + 
      " SELECT id, updated_at AS modified from Orders\r\n" + 
      " UNION\r\n" + 
      " SELECT id, created_at from Orders \r\n" + 
      ") AS whatever ON whatever.id = Orders.id\r\n" + 
      "ORDER BY whatever.modified DESC;\r\n" + 
      ""; 
      try { 
       connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "", ""); 
       preparedStatement = connection.prepareStatement(selectSQL); 
       while (true) { 

        try { 


         ResultSet rs = preparedStatement.executeQuery(selectSQL); 
         while (rs.next()) { 
          Orders order = new Orders(); 
          order.setId(rs.getInt(1)); 
          order.setVendorName(rs.getString(2)); 
          order.setItem(rs.getString(3)); 
          newOrdersList.add(order); 
         } 
         clientResponse = "jsonCallback(["+gson.toJson(newOrdersList)+"])"; 
         Thread.sleep(3000); 
        // System.out.println("clientResponse"+clientResponse); 
         return clientResponse; 
        } catch (InterruptedException e) { 
         e.printStackTrace(); 
        } 
       } 

      } catch (SQLException e) { 
      // System.out.println("Connection Failed! Check output console"); 
       e.printStackTrace(); 

      } 

     } catch (Exception e) { 
      e.printStackTrace(); 
     } 
    // clientResponse = gson.toJson(newOrdersList); 

     return clientResponse; 
    } 

} 

Answer 1

注：這已經answered無數次。

您需要關閉您的jdbc Connection,PreparedStatement和ResultSet對象。

try { 
    connection = DriverManager.getConnection(...) 
    ... 
} catch ... 
... 
} finally { 
    // Each of these needs wrapped in a try/catch block 
    if(resultSet != null) { resultSet.close() } 
    if(preparedStatement != null) { preparedStatement.close() } 
    if(connection != null) { connection.close() } 
} 

當使用JDBC，我通常會寫輔助方法來處理收盤：這是最容易通過添加一個finally塊來你試試月底/ catch塊包裹你的來電getConnection和prepareStatement實現任務。通過將它們放在最後，確保他們始終執行（不管你得到一個異常或在try塊內返回。

Answer 2

您可以使用try與資源功能，將採取關閉連接的護理

try(Connection con=DriverManager.getConnection()){ 
//sql queries 
} 
catch(SQLException ex){ 
//error handling code 
}