At the moment I am writing a Spring and JDBC based web-application that interacts with a MySQL database on a Windows Server 2012 x64. The MySQL database driver is registered by Tomcat and not by the servlet itself (As so many people do).
Although I close all connection/prepared statements/result sets, Tomcat logs a possible memory leak during a restart and I don't know why. Additionally the server crashes (Read: times out) after a few days, maybe because the leaks.
$APACHE_DIR/conf/context.xml:
<?xml version='1.0' encoding='utf-8'?>
<Context>
<WatchedResource>WEB-INF/web.xml</WatchedResource>
<WatchedResource>${catalina.base}/conf/web.xml</WatchedResource>
<Resource name="jdbc/testservlet"
global="jdbc/testservlet"
type="javax.sql.DataSource"
username="root"
password="123456aA"
driverClassName="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/testservlet"
maxTotal="10"
maxIdle="10"
maxWaitMillis="10000"
removeAbandonedTimeout="300"
defaultAutoCommit="true" />
</Context>
$APACHE_DIR/webapps/testservlet/META-INF/context.xml:
<?xml version='1.0' encoding='utf-8'?>
<Context>
<ResourceLink name="jdbc/testservlet" global="jdbc/testservlet" type="javax.sql.DataSource" />
</Context>
$PROJECT_DIR/DatabaseConfiguration.java
package com.example.testservlet.configuration;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.sql.DataSource;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class DatabaseConfiguration
{
@Bean
public DataSource getDataSource() throws Exception
{
Context initialContext = new InitialContext();
Context environmentContext = (Context) initialContext.lookup("java:comp/env");
DataSource dataSource = (DataSource) environmentContext.lookup("jdbc/testservlet");
return dataSource;
}
}
$PROJECT_DIR/HomeController.java
package com.example.testservlet.controller;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.ResultSet;
import javax.sql.DataSource;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;
@Controller
public class HomeController
{
@Autowired
DataSource datasource;
@ResponseBody
@RequestMapping(value = "/", method = RequestMethod.GET)
public void home() throws Exception
{
Connection connection = null;
ResultSet resultset = null;
try
{
connection = datasource.getConnection();
DatabaseMetaData metadata = connection.getMetaData();
resultset = metadata.getTables(null, null, "%", null);
while(resultset.next())
{
System.out.println("Table: " + resultset.getString(3));
}
}
finally
{
System.out.println("Final block start");
try{ connection.close(); } catch(Exception exception) { throw new Exception("Database error"); }
try{ resultset.close(); } catch(Exception exception) { throw new Exception("Database error"); }
System.out.println("Final block end");
}
}
}
$PROJECT_ROOT/pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<modelVersion>4.0.0</modelVersion>
<groupId>com.example</groupId>
<artifactId>testservlet</artifactId>
<packaging>war</packaging>
<version>0.1.0-SNAPSHOT</version>
<name>testservlet</name>
<dependencies>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>4.1.6.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
<version>4.1.6.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>4.1.6.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-jdbc</artifactId>
<version>4.1.6.RELEASE</version>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.38</version>
<scope>provided</scope>
</dependency>
</dependencies>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<build>
<finalName>testservlet</finalName>
<resources>
<resource>
<directory>src/main/resources</directory>
</resource>
</resources>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.3</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<configuration>
<failOnMissingWebXml>false</failOnMissingWebXml>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<classpathPrefix>lib/</classpathPrefix>
</manifest>
</archive>
<webResources>
<resource>
<directory>${project.basedir}/src/main/resources
</directory>
</resource>
</webResources>
</configuration>
</plugin>
</plugins>
</build>
</project>
The MySQL driver is installed as "mysql-connector-java.jar" (Version 5.1.38) inside the Tomcat lib directory also the database configuration is called by the Spring framework. A HTTP request to localhost:8080/testservlet + a Tomcat restarts results in the following log:
25-Jan-2016 19:11:28.006 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Server version: Apache Tomcat/8.0.30
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Server built: Dec 1 2015 22:30:46 UTC
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Server number: 8.0.30.0
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log OS Name: Windows Server 2012 R2
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log OS Version: 6.3
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Architecture: amd64
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Java Home: C:\Program Files\Java\jdk1.8.0_66\jre
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log JVM Version: 1.8.0_66-b18
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log JVM Vendor: Oracle Corporation
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log CATALINA_BASE: C:\Users\simonwaechter\Downloads\apache-tomcat-8.0.30-windows-x64
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log CATALINA_HOME: C:\Users\simonwaechter\Downloads\apache-tomcat-8.0.30-windows-x64
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.util.logging.config.file=C:\Users\simonwaechter\Downloads\apache-tomcat-8.0.30-windows-x64\conf\logging.properties
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.endorsed.dirs=C:\Users\simonwaechter\Downloads\apache-tomcat-8.0.30-windows-x64\endorsed
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Dcatalina.base=C:\Users\simonwaechter\Downloads\apache-tomcat-8.0.30-windows-x64
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Dcatalina.home=C:\Users\simonwaechter\Downloads\apache-tomcat-8.0.30-windows-x64
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.startup.VersionLoggerListener.log Command line argument: -Djava.io.tmpdir=C:\Users\simonwaechter\Downloads\apache-tomcat-8.0.30-windows-x64\temp
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.core.AprLifecycleListener.lifecycleEvent Loaded APR based Apache Tomcat Native library 1.1.33 using APR version 1.5.1.
25-Jan-2016 19:11:28.037 INFO [main] org.apache.catalina.core.AprLifecycleListener.lifecycleEvent APR capabilities: IPv6 [true], sendfile [true], accept filters [false], random [true].
25-Jan-2016 19:11:28.617 INFO [main] org.apache.catalina.core.AprLifecycleListener.initializeSSL OpenSSL successfully initialized (OpenSSL 1.0.1m 19 Mar 2015)
25-Jan-2016 19:11:28.866 INFO [main] org.apache.coyote.AbstractProtocol.init Initializing ProtocolHandler ["http-apr-8080"]
25-Jan-2016 19:11:28.881 INFO [main] org.apache.coyote.AbstractProtocol.init Initializing ProtocolHandler ["ajp-apr-8009"]
25-Jan-2016 19:11:28.881 INFO [main] org.apache.catalina.startup.Catalina.load Initialization processed in 1407 ms
25-Jan-2016 19:11:28.929 INFO [main] org.apache.catalina.core.StandardService.startInternal Starting service Catalina
25-Jan-2016 19:11:28.929 INFO [main] org.apache.catalina.core.StandardEngine.startInternal Starting Servlet Engine: Apache Tomcat/8.0.30
25-Jan-2016 19:11:29.006 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployWAR Deploying web application archive C:\Users\simonwaechter\Downloads\apache-tomcat-8.0.30-windows-x64\webapps\testservlet.war
25-Jan-2016 19:11:30.901 INFO [localhost-startStop-1] org.apache.tomcat.dbcp.dbcp2.BasicDataSourceFactory.getObjectInstance Name = testservlet Ignoring unknown property: value of "JCG Example MySQL database." for "description" property
25-Jan-2016 19:11:30.901 INFO [localhost-startStop-1] org.apache.tomcat.dbcp.dbcp2.BasicDataSourceFactory.getObjectInstance Name = testservlet Ignoring unknown property: value of "jdbc/testservlet" for "global" property
25-Jan-2016 19:11:31.010 INFO [localhost-startStop-1] org.apache.jasper.servlet.TldScanner.scanJars At least one JAR was scanned for TLDs yet contained no TLDs. Enable debug logging for this logger for a complete list of JARs that were scanned but no TLDs were found in them. Skipping unneeded JARs during scanning can improve startup time and JSP compilation time.
25-Jan-2016 19:11:31.213 INFO [localhost-startStop-1] org.springframework.web.context.ContextLoader.initWebApplicationContext Root WebApplicationContext: initialization started
25-Jan-2016 19:11:31.213 INFO [localhost-startStop-1] org.springframework.web.context.support.AnnotationConfigWebApplicationContext.prepareRefresh Refreshing Root WebApplicationContext: startup date [Mon Jan 25 19:11:31 CET 2016]; root of context hierarchy
25-Jan-2016 19:11:31.369 INFO [localhost-startStop-1] org.springframework.web.context.support.AnnotationConfigWebApplicationContext.loadBeanDefinitions Found 2 annotated classes in package [com.example.testservlet.configuration]
25-Jan-2016 19:11:32.141 INFO [localhost-startStop-1] org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping.registerHandlerMethod Mapped "{[/],methods=[GET],params=[],headers=[],consumes=[],produces=[],custom=[]}" onto public void com.example.testservlet.controller.HomeController.home() throws java.lang.Exception
25-Jan-2016 19:11:32.187 INFO [localhost-startStop-1] org.springframework.web.servlet.handler.SimpleUrlHandlerMapping.registerHandler Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.DefaultServletHttpRequestHandler]
25-Jan-2016 19:11:32.437 INFO [localhost-startStop-1] org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.initControllerAdviceCache Looking for @ControllerAdvice: Root WebApplicationContext: startup date [Mon Jan 25 19:11:31 CET 2016]; root of context hierarchy
25-Jan-2016 19:11:32.671 INFO [localhost-startStop-1] org.springframework.web.context.ContextLoader.initWebApplicationContext Root WebApplicationContext: initialization completed in 1458 ms
25-Jan-2016 19:11:32.749 INFO [localhost-startStop-1] org.springframework.web.servlet.DispatcherServlet.initServletBean FrameworkServlet 'DispatcherServlet': initialization started
25-Jan-2016 19:11:32.781 INFO [localhost-startStop-1] org.springframework.web.servlet.DispatcherServlet.initServletBean FrameworkServlet 'DispatcherServlet': initialization completed in 32 ms
25-Jan-2016 19:11:32.829 INFO [localhost-startStop-1] org.apache.catalina.startup.HostConfig.deployWAR Deployment of web application archive C:\Users\simonwaechter\Downloads\apache-tomcat-8.0.30-windows-x64\webapps\testservlet.war has finished in 3,807 ms
25-Jan-2016 19:11:32.829 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["http-apr-8080"]
25-Jan-2016 19:11:32.843 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["ajp-apr-8009"]
25-Jan-2016 19:11:32.843 INFO [main] org.apache.catalina.startup.Catalina.start Server startup in 3959 ms
25-Jan-2016 19:11:45.074 INFO [main] org.apache.catalina.core.StandardServer.await A valid shutdown command was received via the shutdown port. Stopping the Server instance.
25-Jan-2016 19:11:45.074 INFO [main] org.apache.coyote.AbstractProtocol.pause Pausing ProtocolHandler ["http-apr-8080"]
25-Jan-2016 19:11:45.137 INFO [main] org.apache.coyote.AbstractProtocol.pause Pausing ProtocolHandler ["ajp-apr-8009"]
25-Jan-2016 19:11:45.199 INFO [main] org.apache.catalina.core.StandardService.stopInternal Stopping service Catalina
25-Jan-2016 19:11:45.199 INFO [localhost-startStop-2] org.springframework.web.context.support.AnnotationConfigWebApplicationContext.doClose Closing Root WebApplicationContext: startup date [Mon Jan 25 19:11:31 CET 2016]; root of context hierarchy
25-Jan-2016 19:11:45.199 WARNING [localhost-startStop-2] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [testservlet] appears to have started a thread named [Abandoned connection cleanup thread] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.lang.Object.wait(Native Method)
java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:143)
com.mysql.jdbc.AbandonedConnectionCleanupThread.run(AbandonedConnectionCleanupThread.java:43)
25-Jan-2016 19:11:45.215 INFO [main] org.apache.coyote.AbstractProtocol.stop Stopping ProtocolHandler ["http-apr-8080"]
25-Jan-2016 19:11:45.309 INFO [main] org.apache.coyote.AbstractProtocol.stop Stopping ProtocolHandler ["ajp-apr-8009"]
25-Jan-2016 19:11:45.371 INFO [main] org.apache.coyote.AbstractProtocol.destroy Destroying ProtocolHandler ["http-apr-8080"]
25-Jan-2016 19:11:45.371 INFO [main] org.apache.coyote.AbstractProtocol.destroy Destroying ProtocolHandler ["ajp-apr-8009"]
I have no idea why this leak happens. There are many answers like deregistering the JDBC driver, but few of them handle the driver in a shared/hosted Tomcat environment where other servlets might access the same JDBC driver.
