我编写了一个WebService，负责每隔3秒轮询一次DB并发送最新数据
不幸的是，我在一段时间后在我的控制台中收到此异常。
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)
这是我的计划
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;
}
}
答案 0 :(得分：0)
注意：这已经多次answered了。
您需要关闭jdbc Connection，PreparedStatement和ResultSet个对象。最简单的方法是将finally块添加到try / catch块的末尾，包含对getConnection和prepareStatement的调用：
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() }
}
使用JDBC时，我通常会编写辅助方法来处理结束任务。通过将它们放在finally中，您可以确保它们始终被执行（无论您是获得异常还是从try块中返回。
答案 1 :(得分：0)
您可以使用 try资源功能来处理关闭连接
try(Connection con=DriverManager.getConnection()){
//sql queries
}
catch(SQLException ex){
//error handling code
}