Struct JavaRunner 

pub struct JavaRunner { /* private fields */ }

A builder for configuring and executing a Java program (JAR or main class).

This struct allows you to set the Java runtime, JAR file or main class, arbitrary tool arguments, memory limits, program arguments, and I/O redirection before spawning the process.

Examples

Run a JAR:

use java_manager::{JavaRunner, JavaRedirect};

JavaRunner::new()
    .java(java)
    .jar("myapp.jar")
    .min_memory(256 * 1024 * 1024)   // 256 MB
    .max_memory(1024 * 1024 * 1024)  // 1 GB
    .arg("--server")
    .redirect(JavaRedirect::new().output("out.log").error("err.log"))
    .execute()?;

Run a tool command (no JAR or main class needed):

JavaRunner::new()
    .java(java)
    .cmd(&["-version"])
    .execute()?;

Implementations

impl JavaRunner

pub fn new() -> Self

Creates a new builder with default settings.

pub fn java(self, java: JavaInfo) -> Self

Sets the Java installation to use.

This is mandatory before calling execute.

pub fn jar(self, jar: impl AsRef<Path>) -> Self

Sets the JAR file to execute (implies the -jar flag).

Either jar or main_class must be set.

pub fn min_memory(self, bytes: usize) -> Self

Sets the initial heap size (-Xms).

The value is given in bytes and will be formatted as a memory string (e.g., 256m, 1g). If the size is not a multiple of a megabyte or gigabyte, it will be rounded to the nearest megabyte.

pub fn max_memory(self, bytes: usize) -> Self

Sets the maximum heap size (-Xmx).

See min_memory for formatting details.

pub fn main_class(self, class: impl Into<String>) -> Self

Sets the main class to execute (instead of a JAR file).

Either jar or main_class must be set.

pub fn cmd(self, args: &[&str]) -> Self

Sets arbitrary tool arguments for the Java command (no JAR or main class).

Use this to run commands like java -version, java --list-modules, or java -XshowSettings. When cmd_args is set, the jar and main_class requirements are bypassed.

Examples

JavaRunner::new()
    .java(java)
    .cmd(&["-version"])
    .execute()?;

pub fn arg(self, arg: impl Into<String>) -> Self

Adds a single argument to be passed to the Java program.

Arguments are appended in the order they are added.

pub fn redirect(self, redirect: JavaRedirect) -> Self

Sets I/O redirection options.

pub fn classpath(self, paths: &[impl AsRef<Path>]) -> Self

Sets the classpath (-cp / -classpath).

Paths are joined with the platform-specific separator (; on Windows, : otherwise).

pub fn module_path(self, path: impl AsRef<Path>) -> Self

Sets the module path (--module-path).

pub fn add_opens( self, module: impl Into<String>, package: impl Into<String>, target: impl Into<String>, ) -> Self

Adds a --add-opens flag (e.g., java.base/java.lang=ALL-UNNAMED).

pub fn add_exports( self, module: impl Into<String>, package: impl Into<String>, target: impl Into<String>, ) -> Self

Adds a --add-exports flag (e.g., java.base/com.sun.internal=ALL-UNNAMED).

pub fn system_property( self, key: impl Into<String>, value: impl Into<String>, ) -> Self

Sets a system property (-Dkey=value).

pub fn env(self, key: impl Into<String>, value: impl Into<String>) -> Self

Sets an environment variable for the child Java process.

pub fn working_dir(self, path: impl AsRef<Path>) -> Self

Sets the working directory for the child Java process.

pub fn timeout(self, duration: Duration) -> Self

Sets a timeout for the Java process.

If the process runs longer than the specified duration, it will be killed. A Duration::ZERO or None means no timeout.

pub fn execute(&self) -> Result<(), JavaError>

Executes the configured Java program.

When cmd_args is set, the JAR / main-class requirement is bypassed and the provided arguments are passed directly to java.

Errors

Returns JavaError::Other if no Java installation has been set, or if neither a JAR file nor a main class (nor cmd arguments) has been specified. Returns JavaError::NotFound if the Java executable does not exist. Returns JavaError::IoError if file operations or process spawning fail. Returns JavaError::ExecutionFailed if the Java process exits with a non‑zero status.

Trait Implementations

impl Debug for JavaRunner

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for JavaRunner

fn default() -> JavaRunner

Returns the “default value” for a type.