The Method 2 is to use the WrapperStartStopApp helper class.
This method provides a way to integrate with applications like Tomcat,
which are started using one class and then stopped using another class.
Typically, this kind of application will open a server socket on startup whose job is to wait for a connection that triggers a shutdown.
The shutdown or stop class,
triggers the shutdown by connecting to application when launched.
The Wrapper works with this kind of application by starting up the application, as in Method 1, using the
start class and then calling the main method of the
stop class when it is time for the application to be shut down.
When integrating with this Method 2, the WrapperStartStopApp helper class replaces an application's main class.
This gives the WrapperStartStopApp class a chance to immediately initialize
the WrapperManager and register the JVM with the Wrapper.
The WrapperStartStopApp class then manages all interaction with the Wrapper as well as the life-cycle of an application.
When the Wrapper sends a start message to the JVM via the WrapperManager,
the main method of the application's start class is called.
Likewise, when the Wrapper sends a stop message, the main method of the application's stop class is called.
When the WrapperStartStopApp helper class is launched, it needs to be told about the
class names of both the start and stop
classes, as well as any parameters thata need to be provided to the main methods of each class.
This results in a parameter list that is a little
more complicated than that of the Method 1 (WrapperSimpleApp) helper class.
The first parameter passed to the WrapperStartStopApp class
will be the full class name of the start class.
This is followed by a count of the parameters to the start class's main method, which will come next.
After the start class's parameters, comes the stop class's full class name.
This is followed by a TRUE/FALSE flag that tells the WrapperStartStopApp class
whether or not it should wait until all non-daemon threads have completed before actually exiting.
This flag is then followed by the stop class's parameter count and parameters.
Don't worry if this is confusing right now.
A detailed example is provided below.
This section will walk you through a detailed explanation
of how to configure Tomcat
to run within the Wrapper.
Most other applications can be integrated by following the same steps.
This tutorial will start with a clean install of Tomcat.
We used Tomcat 9.0.0.M13, so the exact steps may be slightly different depending on the version you installed.
Tomcat was installed in the root directory, D:\,
resulting in a Tomcat home directory of D:\apache-tomcat-9.0.0.M13.
Installing Wrapper Files
There are four directories that are required to be configured in order to be able to use the Wrapper.
First, copy the following files into the Tomcat bin directory:
The wrapper.exe file is the actual Wrapper executable.
The three batch files are used to run Tomcat in a console, and to install and uninstall it as a Windows Service.
These batch files should not require any modification.
They do assume that the wrapper.conf file will be located
within a conf directory (one level up, ../conf/wrapper.conf).
If you wish to place the wrapper.conf file somewhere else,
then the three batch files will require appropriate modification.
Copy the following two files into the lib directory of Tomcat:
The wrapper.dll file is a native library file
required by the portion of the Wrapper that runs within the JVM.
The wrapper.jar file contains all of the Wrapper classes.
The Wrapper requires a configuration file wrapper.conf for each application.
The standard location for this file is in a conf directory in the application's home directory.
Copy the following template file wrapper.conf.in into the conf directory of Tomcat.
Rename the file as follows.
Be sure to remove the .in extension, so that the file is named wrapper.conf.
You should now have:
If you wish to relocate the configuration file wrapper.conf, you are free to do so.
You will need to modify the batch files copied into the bin directory above to reflect the new location.
The default configuration file wrapper.conf will place a
wrapper.log file in a logs directory under the application's home directory.
Tomcat already has such a directory, so we are all set.
If you wish to place the wrapper.log file in another location,
you will need to edit the wrapper.conf file
and modify the wrapper.logfile property to reflect the new location.
Locate the Application's Java Command Line
Before the Wrapper can be configured to launch an application,
you will need to know the full Java command that is normally used.
Most applications make use of a batch file to build up the actual command line.
These batch files tend to get quite unwieldy,
but in fact, the featured ability to avoid having to work with them is
one of the benefits of working with the Wrapper.
Tomcat is launched by default using a batch file called startup.bat
and then shutdown using a batch file called shutdown.bat.
It is launched by first changing the current directory to the
bin directory and then run from there.
If you open startup.bat into an editor, you will notice after some
investigation that Java is not actually launched from this batch file.
Rather another batch file, catalina.bat, is called.
Tomcat's scripts are very advanced and allow the user
to do a lot of configuration from the command line.
The command line that we will capture and use with the Wrapper will actually be a snapshot of one such configuration.
This example will assume that no parameters are passed to either the startup or shutdown scripts when they are run.
If you open catalina.bat into an editor and scroll
down to the very bottom of the file, you will see four lines that launch Java.
With the defaults that we are using, the first of these will be used.
The line we are interested in looks like the following: (The command is very long and has been truncated.)
The majority of the script has the task of collecting system-specific information
and storing that information into environment variables.
The line above then expands all of the collected information
into the final Java command that launches the application.
From looking at the source of the batch file,
we hope you appreciate the complexity and the desire to have to
avoid completely writing such scripts yourself.
In order to configure the Wrapper, all that is really needed is the final expanded command line.
Rather than reading through the entire script and attempting to understand it,
we will use a simple trick to display the final command line in the console.
Edit the batch file catalina.bat by inserting ECHO at the beginning of the above line.
After doing so, you should have:(Once again the line has been truncated to fit on the screen.)
We now need to repeat the same process for the batch file shutdown.bat
as well as startup.bat above.
You may be surprised to find that if you simply run it now, you will get the following output.
This is because both startup.bat and shutdown.bat call
catalina.bat only changing a parameter.
Other than the start Tomcat at the beginning of the startup line, the two commands are almost identical.
The only difference is the parameter passed to the main class at the end.
The start Tomcat portion of the command is only used to spawn Tomcat into its own console.
This is not required when using the Wrapper, so the rest of this example will ignore that portion of the command.
The Wrapper will also handle the quoting of elements of the Java command line that it builds up.
So it is not necessary for them to be carried over into the configuration file wrapper.conf below.
Modifying the "wrapper.conf" File
In order to use the above Java command line with the Wrapper,
we need to break up the command line's components into a configuration file.
Open the wrapper.conf
file into an editor and make the changes as shown below.
We have provided some links where you will find the description for the properties mentioned.
Please take the time to review the descriptions of any properties that are modified.
In many cases, you can find complete details on their usage that are not mentioned here.
First, extract the Java executable and assign the location path to the property:
Most applications provide a number of parameters to the Java executable when it is launched.
The Java Service Wrapper provides special properties to configure things like memory, as well as class and library paths.
These will be covered below; however, any other settings are configured using the
wrapper.java.additional.<n> series of properties.
The Tomcat command line has several of these properties:
# Following properties are optional:
Note that all quotes have been removed as none of these paths will ever contain quotes.
See the property documentation about how to handle properties containing spaces.
Now we have the classpath, which is configured using the properties
The Wrapper requires that the classpath be broken up into its individual elements.
Since we will use the Java Service Wrapper, it is necessary to include the wrapper.jar file as well:
The next component of the command used to launch Tomcat is the main class org.apache.catalina.startup.Bootstrap.
The main class executed by Java when launched is specified by using the
As mentioned above; however, because we are making use of the WrapperStartStopApp
helper class to start and stop Tomcat, we will specify that class's full name as the main class.
The Tomcat main classes are then specified as application parameters below.
Complete details to configure these properties are available by visiting the
wrapper.app.parameter.<n> property page.
Application parameters appear in the Java command line, directly after the main class.
When we use the WrapperStartStopApp helper class, a lot of information needs
to be provided about both the start and stop classes.
This information includes each class's full name, the list of parameters passed to their main methods, and a flag instructing
the helper class whether or not it should wait for all non-daemon threads to exit before causing the JVM to exit.
We will explain how this information is encoded as follows.
We start by presenting the property values for the Tomcat application.
Several comments have been already added above, specifically about what you can normally find
in the wrapper.conf file.
It will be easy to understand what each property means.
We suggest to add these comments to your configuration file wrapper.conf as well.
# The first application parameter is the name of the class whose main
# method is to be called when the application is launched. The class
# name is followed by the number of parameters to be passed to its main
# method. Then comes the actual parameters.
# The start parameters are followed by the name of the class whose main
# method is to be called to stop the application. The stop class name
# is followed by a flag that controls whether or not the Wrapper should
# wait for all non daemon threads to complete before exiting the JVM.
# The flag is followed by the number of parameters to be passed to the
# stop class's main method. Finally comes the actual parameters.
The start and stop class names should be clear now.
The first parameter count is required to locate the stop class in the parameter list.
The second count is there for consistency.
The flag at parameter #5 above, is used to control the behavior of the
WrapperStartStopApp helper class when it is shutting down the JVM.
When the Wrapper sends a JVM shutdown request, WrapperStartStopApp responds by
calling the main method of the stop class with the configured parameters.
The flag above controls what happens when that main method returns.
If the flag is FALSE, then System.exit(0) will be called immediately.
When TRUE, WrapperStartStopApp will wait until all non-daemon
threads have completed before calling System.exit(0).
The latter is the behavior that produces the cleanest shutdown for Tomcat.
If TRUE is specified but one or more Daemon threads do not complete, the Wrapper will forcibly kill
the JVM after its Shutdown Timeout has expired.
The timeout set by default is 30 seconds.
Non-daemon threads are counted by iterating over all threads in the
system and counting those whose isDaemon method returns FALSE.
Unfortunately, this count will never actually reach "0" (zero) on most JVMs
because of the existence of system threads.
In most Oracle Hotspot JVMs, there will be one non-daemon system thread.
In order to make the shutdown work correctly, this system thread count needs to be correct as well.
It can be set by defining system property:
The default value is 1 thread.
If the main method of the stop class calls System.exit
from within its main thread, that thread will in effect become deadlocked by that call.
The Wrapper avoids a deadlock by detecting this and proceeding with the shutdown after 5 seconds.
However, this may result in the application failing to shutdown cleanly on its own, and should be avoided where possible.
This case can be tested for by enabling the wrapper.debug=TRUE property.
After that, review the log file during the shutdown process.
In order to use the Wrapper, one more property must be set.
The Wrapper makes use of a native library to control interactions with the system.
This library filewrapper.dll
needs to be specified on the library path supplied to the JVM.
Tomcat does not have any native libraries of its own, but if it did,
the directories where they were located would also need to be specified.
Notice, while these configurations will work correctly on this particular machine,
it is highly dependent on the directory structure and platform.
By taking advantage of the fact that the Wrapper always sets the working directory
to the location of the wrapper.exe file and also by making use of a single environment variable, we are able to modify the above properties.
This way they are completely platform and machine independent.
It has been reported that Tomcat 5.0.28 will not work correctly if the bin directory
is included in the java.endorsed.dirs system property.
This is caused by a change in Tomcat, rather than any issue with the Wrapper.
Please modify the above configuration as follows:
The final step is to set the Windows Service Properties.
We will just set the properties that should be changed, but there are several others available.
Please read the documentation for details on their usage.
Suggested values for these variables are shown below.
wrapper.ntservice.displayname=Tomcat Application Server
wrapper.ntservice.description=Tomcat Application Server
Trying It Out
Tomcat can now be run by simply executing the batch file bin\Tomcat.bat.
Because of the way the Wrapper sets its current directory, it is not necessary to run this batch
file from within the bin directory.
Please try running the application once as a console application
to verify the configuration before attempting to run it as a service.
Congratulations. Your application should now be up and running.
If you have any problems, please take a look at the
section for help with tracking down the problem.
Tuning The Startup
By default, the
class will wait 2 seconds for the user application's main method to complete.
After that, it assumes that the application has started and reports back to the Wrapper process.
This is done because many user applications are written with main methods that do not return for the life of the application.
In such cases, there is no reliable way for the WrapperStartStopApp class to tell
when and if the application has completed its startup.
If, however, it is known that the application's main method will return once the application is started,
it would be ideal for the Wrapper to wait until it has done so before continuing.
waitForStartMain System Property:
For main methods that return in this way, the WrapperStartStopApp looks for the
If it is set to TRUE, the WrapperStartStopApp will wait indefinitely for the main method to complete.
Waiting indefinitely is an advantageous option
if it is known for sure that the main method will return in a timely manner.
But on the other hand, while it is waiting eternally,
the Wrapper will never give up on the startup process, no matter how long it takes.
So, if there is any chance that this startup could hang, then
system property to set the maximum wait time may be a better option.
For instance, to wait for up to 5 minutes (300 seconds) for the startup main method to complete,
set the property to 300 as follows:
The main methods of many applications are designed not to return.
In these cases, you must either stick with the default 2-second startup timeout or specify a slightly longer timeout, using the
maxStartMainWait property, to simulate the amount of time your application takes to start up.
If TRUE in the waitForStartMain is specified for an application
whose start method never returns, the Wrapper will appear at first to be functioning correctly.
However, the Wrapper is actually in a wait status eternally and will never enter a running state, which means
that the Windows Service Manager and several of the Wrapper's error recovery mechanisms will not function correctly.