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Java Options Framework

The Java Options Framework contributes arbitrary Java options to the application at runtime.

Detection Criterion java_opts set in the config/java_opts.yml file or the JAVA_OPTS environment variable set
Tags java-opts
Tags are printed to standard output by the buildpack detect script

Configuration

For general information on configuring the buildpack, including how to specify configuration values through environment variables, refer to Configuration and Extension.

The framework can be configured by creating or modifying the config/java_opts.yml file in the buildpack fork.

Name Description
from_environment Whether to append the value of the JAVA_OPTS environment variable to the collection of Java options
java_opts The Java options to use when running the application. All values are used without modification when invoking the JVM. The options are specified as a single YAML scalar in plain style or enclosed in single or double quotes.

Any JAVA_OPTS from either the config file or environment variables will be specified in the start command after any Java Opts added by other frameworks.

Runtime variable expansion

Java options are assembled at container start by the buildpack's profile.d script (00_java_opts.sh), then passed to the JVM by the shell-free javaexec launcher. Because javaexec tokenizes JAVA_OPTS without invoking a shell, characters such as *, &, ;, |, and > are treated as literals — they reach the JVM exactly as written.

Environment variable references

$VARNAME and ${VARNAME} references in both JAVA_OPTS (env) and java_opts (config) are expanded at container start against the runtime environment:

# $PWD, $HOME, $PORT, and any CF-injected variable all work
cf set-env my-application JAVA_OPTS '-Dapp.config=$PWD/config/app.properties'
cf set-env my-application JAVA_OPTS '-Dserver.port=$PORT'
# config/java_opts.yml
java_opts: '-Xloggc:$PWD/beacon_gc.log -verbose:gc'

Command substitutions are never executed

$(...) and backtick command substitutions are not executed. A value such as -Dinject=$(hostname) reaches the JVM as the literal string -Dinject=$(hostname). This is intentional: executing arbitrary commands from a user-supplied option string would be a security vulnerability.

Processor count: $(nproc)

The one exception is -XX:ActiveProcessorCount=$(nproc), which the buildpack itself emits for JRE vendors that need it. The profile.d script resolves this single known token to the actual CPU count before passing the option to the JVM. Any other $(...) expression passes to the JVM literally.

Special characters and quoting

Characters that were shell-special under the old eval-based launcher (*, &, ;, |, >) are now passed to the JVM as literals — no quoting tricks required.

POSIX quoting in the assembled JAVA_OPTS string is respected by javaexec's tokenizer: a quoted value such as "-Dfoo=bar baz" is delivered as the single argument -Dfoo=bar baz.

Want to pass to JVM Write in JAVA_OPTS / java_opts
Literal $PORT (no expansion) \$PORT
Literal \ backslash \\
Literal \\ two backslashes \\\\
Value of $PORT at runtime $PORT
Cron expression 0 */7 * * * 0 */7 * * * (no quoting needed)
Space inside one JVM arg "-Dfoo=bar baz" (quote the arg) 
# Expand $PORT at runtime
cf set-env my-application JAVA_OPTS '-Dserver.port=$PORT'

# Literal $PORT — not expanded
cf set-env my-application JAVA_OPTS '-Dexample.literal=\$PORT'

# Windows-style path — \\ becomes one backslash
cf set-env my-application JAVA_OPTS '-Dapp.data=C:\\data\\app'

# Cron expression — * is not glob-expanded
cf set-env my-application JAVA_OPTS '-DcronExpr=0 */7 * * *'

Note: $ followed by a digit or non-identifier character (e.g. $1, $.) is left as-is. Undefined variables expand to an empty string.

Migrating from the Ruby buildpack? See Migrating JAVA_OPTS escaping from the Ruby buildpack for a comparison of the escaping rules.

Examples

Configuration File Example

# config/java_opts.yml
---
from_environment: false
java_opts: -Xloggc:$PWD/beacon_gc.log -verbose:gc

Environment Variable Override Examples

To override the configuration via the JBP_CONFIG_JAVA_OPTS environment variable, use YAML flow style (inline YAML) with curly braces:

Example 1: Using an array of options (recommended)

cf set-env my-application JBP_CONFIG_JAVA_OPTS '{ java_opts: ["-Xms256m", "-Xmx1024m", "-XX:+UseG1GC"] }'

Or in the application manifest:

env:
  JBP_CONFIG_JAVA_OPTS: '{ java_opts: ["-Xms256m", "-Xmx1024m", "-XX:+UseG1GC"] }'

Example 2: Disabling from_environment

cf set-env my-application JBP_CONFIG_JAVA_OPTS '{ from_environment: false, java_opts: ["-Xmx512m"] }'

Example 3: Multiple JVM options

env:
  JBP_CONFIG_JAVA_OPTS: '{ from_environment: false, java_opts: ["-Xmx512M", "-Xms256M", "-Xss1M", "-XX:MetaspaceSize=157286K", "-XX:MaxMetaspaceSize=314572K"] }'

Note: For backward compatibility, a space-separated string is also supported:

env:
  JBP_CONFIG_JAVA_OPTS: '{ java_opts: "-Xmx512M -Xms256M" }'

However, using an array format is recommended for clarity and to avoid parsing ambiguities.

Allowed Memory Settings

Argument Description
-Xms Minimum or initial size of heap.
-Xss Size of each thread's stack. This could effect the total heap size. JRE Memory
-XX:MaxMetaspaceSize The maximum size Metaspace can grow to. This could effect the total heap size. JRE Memory
-XX:MaxPermSize The maximum size Permgen can grow to. Only applies to Java 7. This could effect the total heap size. JRE Memory
-Xmn <SIZE> Maximum size of young generation, known as the eden region.
-XX:+UseGCOverheadLimit Use a policy that limits the proportion of the VM's time that is spent in GC before an java.lang.OutOfMemoryError error is thrown.
-XX:+UseLargePages Use large page memory. For details, see Java Support for Large Memory Pages.
-XX:-HeapDumpOnOutOfMemoryError Dump heap to file when java.lang.OutOfMemoryError is thrown.
-XX:HeapDumpPath=<PATH> Path to directory or filename for heap dump.
-XX:LargePageSizeInBytes=<SIZE> Sets the large page size used for the Java heap.
-XX:MaxDirectMemorySize=<SIZE> Upper limit on the maximum amount of allocatable direct buffer memory. This could effect the total heap size. JRE Memory
-XX:MaxHeapFreeRatio=<RATIO> Maximum percentage of heap free after GC to avoid shrinking.
-XX:MaxNewSize=<SIZE> Maximum size of new generation. Since 1.4, MaxNewSize is computed as a function of NewRatio.
-XX:MinHeapFreeRatio=<RATIO> Minimum percentage of heap free after GC to avoid expansion.
-XX:NewRatio=<RATIO> Ratio of old/new generation sizes. 2 is equal to approximately 66%.
-XX:NewSize=<SIZE> Default size of new generation.
-XX:OnError="<CMD ARGS>;<CMD ARGS>" Run user-defined commands on fatal error.
-XX:ReservedCodeCacheSize=<SIZE> Java 8 Only Maximum code cache size. Also know as -Xmaxjitcodesize. This could effect the total heap size. JRE Memory
-XX:SurvivorRatio=<RATIO> Ratio of eden/survivor space. Solaris only.
-XX:TargetSurvivorRatio=<RATIO> Desired ratio of survivor space used after scavenge.