VM parameters

## VM parameters |

### 1. Fixed VM parameters

Fixed VM parameters can be configured in the launcher wizard where you can use compiler variables to handle platform-specific changes or launcher variables to use runtime-dependent variable in your VM parameters.

### 2. *.vmoptions files

A common requirement is to adjust the VM parameters of your application launchers depending on the runtime environment like the target platform or some user selection in the installer.

In addition to the fixed VM parameters, a parameter file in the same directory as the executable is read and its contents are added to the existing VM parameters. The name of this parameter file is the same as the executable file with the extension `.vmoptions`. For example, if your executable is named `hello.exe`, the name of the VM parameter file is `hello.vmoptions`. In this file, each line is interpreted as a single VM parameter. The last line must be followed by a line feed. install4j adapts your .vmoptions files during the compilation phase so that the line endings are suitable for all platforms. For example, the contents of the VM parameter file could be:

    -Xmx128m
    -Xms32m

The `*.vmoptions` files allow the installer as well as expert users to modify the VM parameters for your application launchers.

In addition to the VM parameters you can also modify the classpath in the `*.vmoptions` files with the following options:

- -classpath [classpath]
  Replace the classpath of the generated launcher.
- -classpath/a [classpath]
  Append to the classpath of the generated launcher.
- -classpath/p [classpath]
  Prepend to the classpath of the generated launcher.

For GUI launchers on Mac OS X, the VM options are stored in a file called `Info.plist` inside the application bundle. The "Add VM options" action described below handles these platform-specific differences.

### 3. Environment variables

You can use environment variables in the VM parameters and the `.vmoptions` file with the syntax `${variableName}` where you replace `variableName` with the desired environment variable.

This environment variable syntax also works in the arguments text field and the classpath configuration.

### 4. "Add VM options" action

In order to handle VM parameter additions in the installer in a cross-platform fashion, install4j includes an "Add VM options" action that adds VM parameters to the `*.vmoptions` file on Microsoft Windows and Unix and modifies the `Info.plist` file on Mac OS X.

The Add VM options action creates a `*.vmoptions` file if necessary or adds your options to the `*.vmoptions` file if it already exists. However, a number of VM parameters can only occur once so the action replaces the following parameters if they already exist:

- -Xmx
- -Xms
- -Xss
- -Xloggc
- -Xbootclasspath
- -verbose
- -ea / -enableassertions
- -da / -disableassertions
- -agentlib
- -agentpath
- -javaagent
- -splash

as well as the install4j-specific classpath modification options (see above).

To set an -Xmx value that depends on the total memory of the target system, you can use a "Set a variable action" to calculate the numeric part of the -Xmx value using the utility method `SystemInfo.getPhysicalMemory()` and use that variable in the "VM options" property of the "Add VM options" action. For example, in order to use 50% of the total memory for the maximum heap size, you do the following after the "Install files" action:

1. Add a "Set a variable" action with variable name "xmx" and expression

                 "-Xmx" + Math.round(SystemInfo.getPhysicalMemory() * 0.5 / 1024 / 1024) + "m"

2. Add a "Add VM options" action with VM options

               "${installer:xmx}".