尝试通过Servlet连接到MongoDB时，Tomcat服务器无法

Question

Following is the servlet doget code:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub      
    String message = "Hello World";
    request.setAttribute("message", message); // This will be available as ${message}
    request.getRequestDispatcher("/WEB-INF/hello.jsp").forward(request, response);

    /*response.getWriter().println("<h2>Hello friend!</h2>");
}

When run the above code on tomcat server, its executing.

But not when I work with the mongodb database. The new code which doesn't run the server is as follows:

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    MongoClient mongo = new MongoClient("localhost", 27017);

    /**** Get database ****/
    // if database doesn't exists, MongoDB will create it for you
    DB db = mongo.getDB("testdb");

    /**** Get collection / table from 'testdb' ****/
    // if collection doesn't exists, MongoDB will create it for you
    DBCollection table = db.getCollection("user");

    /**** Insert ****/
    // create a document to store key and value
    BasicDBObject document = new BasicDBObject();
    document.put("name", "mkyong");
    document.put("age", 30);
    document.put("createdDate", new Date());
    table.insert(document);

    /**** Find and display ****/
    BasicDBObject searchQuery = new BasicDBObject();
    searchQuery.put("name", "mkyong");

    DBCursor cursor = table.find(searchQuery);

    while (cursor.hasNext()) {
        System.out.println(cursor.next());
    }


    String message = "Hello World";
    request.setAttribute("message", message); // This will be available as ${message}
    request.getRequestDispatcher("/WEB-INF/hello.jsp").forward(request, response);

    /*response.getWriter().println("<h2>Hello friend!</h2>");*/



}

generated error: Server Tomcat v7.0 Server at localhost failed to start.

Why is that?

complete console output:

Mar 03, 2017 3:18:12 PM org.apache.tomcat.util.digester.SetPropertiesRule begin
WARNING: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property 'source' to 'org.eclipse.jst.jee.server:MyFirstServlet' did not find a matching property.
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Server version:        Apache Tomcat/7.0.75
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Server built:          Jan 18 2017 20:54:42 UTC
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Server number:         7.0.75.0
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: OS Name:               Windows 7
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: OS Version:            6.1
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Architecture:          x86
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Java Home:             C:\Program Files (x86)\Java\jre1.8.0_121
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: JVM Version:           1.8.0_121-b13
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: JVM Vendor:            Oracle Corporation
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: CATALINA_BASE:         D:\eclipse-workspace-j\.metadata\.plugins\org.eclipse.wst.server.core\tmp0
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: CATALINA_HOME:         C:\Program Files (x86)\Apache Software Foundation\Tomcat 7.0
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dcatalina.base=D:\eclipse-workspace-j\.metadata\.plugins\org.eclipse.wst.server.core\tmp0
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dcatalina.home=C:\Program Files (x86)\Apache Software Foundation\Tomcat 7.0
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dwtp.deploy=D:\eclipse-workspace-j\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Djava.endorsed.dirs=C:\Program Files (x86)\Apache Software Foundation\Tomcat 7.0\endorsed
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.VersionLoggerListener log
INFO: Command line argument: -Dfile.encoding=Cp1252
Mar 03, 2017 3:18:12 PM org.apache.catalina.core.AprLifecycleListener lifecycleEvent
INFO: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: C:\Program Files (x86)\Java\jre1.8.0_121\bin;C:\Windows\Sun\Java\bin;C:\Windows\system32;C:\Windows;C:/Program Files (x86)/Java/jre1.8.0_121/bin/client;C:/Program Files (x86)/Java/jre1.8.0_121/bin;C:/Program Files (x86)/Java/jre1.8.0_121/lib/i386;C:\ProgramData\Oracle\Java\javapath;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files\MATLAB\R2013a\runtime\win64;C:\Program Files\MATLAB\R2013a\bin;C:\Program Files (x86)\Skype\Phone\;C:\eclipse;;.
Mar 03, 2017 3:18:12 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-bio-8080"]
Mar 03, 2017 3:18:12 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-bio-8009"]
Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 526 ms
Mar 03, 2017 3:18:12 PM org.apache.catalina.core.StandardService startInternal
INFO: Starting service Catalina
Mar 03, 2017 3:18:12 PM org.apache.catalina.core.StandardEngine startInternal
INFO: Starting Servlet Engine: Apache Tomcat/7.0.75
Mar 03, 2017 3:18:12 PM org.apache.catalina.core.ContainerBase startInternal
SEVERE: A child container failed during start
java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/MyFirstServlet]]
    at java.util.concurrent.FutureTask.report(Unknown Source)
    at java.util.concurrent.FutureTask.get(Unknown Source)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1119)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:819)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1571)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1561)
    at java.util.concurrent.FutureTask.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/MyFirstServlet]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:162)
    ... 6 more
Caused by: java.lang.NoClassDefFoundError: com/mongodb/DBObject
    at java.lang.Class.getDeclaredFields0(Native Method)
    at java.lang.Class.privateGetDeclaredFields(Unknown Source)
    at java.lang.Class.getDeclaredFields(Unknown Source)
    at org.apache.catalina.util.Introspection.getDeclaredFields(Introspection.java:106)
    at org.apache.catalina.startup.WebAnnotationSet.loadFieldsAnnotation(WebAnnotationSet.java:270)
    at org.apache.catalina.startup.WebAnnotationSet.loadApplicationServletAnnotations(WebAnnotationSet.java:139)
    at org.apache.catalina.startup.WebAnnotationSet.loadApplicationAnnotations(WebAnnotationSet.java:65)
    at org.apache.catalina.startup.ContextConfig.applicationAnnotationsConfig(ContextConfig.java:417)
    at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:891)
    at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:388)
    at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:117)
    at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:90)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5522)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
    ... 6 more
Caused by: java.lang.ClassNotFoundException: com.mongodb.DBObject
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1892)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1735)
    ... 20 more

Mar 03, 2017 3:18:12 PM org.apache.catalina.core.ContainerBase startInternal
SEVERE: A child container failed during start
java.util.concurrent.ExecutionException: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost]]
    at java.util.concurrent.FutureTask.report(Unknown Source)
    at java.util.concurrent.FutureTask.get(Unknown Source)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1119)
    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:300)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
    at org.apache.catalina.core.StandardService.startInternal(StandardService.java:444)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
    at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:758)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:693)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:294)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:428)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:162)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1571)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1561)
    at java.util.concurrent.FutureTask.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: org.apache.catalina.LifecycleException: A child container failed during start
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1127)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:819)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
    ... 6 more

Mar 03, 2017 3:18:12 PM org.apache.catalina.startup.Catalina start
SEVERE: The required Server component failed to start so Tomcat is unable to start.
org.apache.catalina.LifecycleException: Failed to start component [StandardServer[8005]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:162)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:693)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:294)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:428)
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardService[Catalina]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:162)
    at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:758)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
    ... 7 more
Caused by: org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina]]
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:162)
    at org.apache.catalina.core.StandardService.startInternal(StandardService.java:444)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
    ... 9 more
Caused by: org.apache.catalina.LifecycleException: A child container failed during start
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:1127)
    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:300)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:145)
    ... 11 more

Mar 03, 2017 3:18:12 PM org.apache.coyote.AbstractProtocol pause
INFO: Pausing ProtocolHandler ["http-bio-8080"]
Mar 03, 2017 3:18:12 PM org.apache.coyote.AbstractProtocol pause
INFO: Pausing ProtocolHandler ["ajp-bio-8009"]
Mar 03, 2017 3:18:12 PM org.apache.catalina.core.StandardService stopInternal
INFO: Stopping service Catalina
Mar 03, 2017 3:18:12 PM org.apache.coyote.AbstractProtocol destroy
INFO: Destroying ProtocolHandler ["http-bio-8080"]
Mar 03, 2017 3:18:12 PM org.apache.coyote.AbstractProtocol destroy
INFO: Destroying ProtocolHandler ["ajp-bio-8009"]

Answer 1

It is look like that your mongodb lib is missing in libraries

java.lang.ClassNotFoundException

it means that Java cannot find class to load