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Installation

jre_downloader is the pair of helpers that turn a (distribution, version) into a path to a working java binary.

API

// With `events`
pub async fn jre_download<F>(
    runtimes_folder: &Path,
    distribution: &JavaDistribution,
    version: &u8,
    on_progress: F,
    event_bus: Option<&EventBus>,
) -> JreResult<PathBuf>
where F: Fn(u64, u64);

// Without `events`
pub async fn jre_download<F>(
    runtimes_folder: &Path,
    distribution: &JavaDistribution,
    version: &u8,
    on_progress: F,
) -> JreResult<PathBuf>
where F: Fn(u64, u64);

// Available regardless of feature
pub async fn find_java_binary(
    runtimes_folder: &Path,
    distribution: &JavaDistribution,
    version: &u8,
) -> JreResult<PathBuf>;

Both helpers apply JavaDistribution::get_fallback(version) internally, so calling them with a (distribution, version) that isn't published on the current platform still returns a working binary path (from the fallback). The same logic lets find_java_binary locate an install made by jre_download with no extra bookkeeping.

Pipeline

sequenceDiagram
    participant App
    participant Downloader as jre_download
    participant FS
    participant API as Provider API
    participant Core as lighty_core

    App->>Downloader: jre_download(dir, dist, 21, cb)
    Downloader->>FS: clear / create dir
    Downloader->>API: get_download_url(21)
    API-->>Downloader: URL
    Downloader->>Core: download_file(URL, cb)
    Core-->>Downloader: archive bytes (Vec<u8>)
    Downloader->>Core: zip_extract / tar_gz_extract
    Downloader->>FS: locate java binary
    Downloader-->>App: PathBuf
Loading

Disk layout

<runtimes_folder>/
└── <distribution>_<version>/
    └── <jre_root>/                    # whatever the archive ships
        ├── bin/java[.exe]             # Linux / Windows / Liberica macOS
        └── Contents/Home/bin/java     # macOS bundles (Temurin, Zulu)

Example after jre_download(<cache>/java, &Temurin, &21, …):

~/.cache/LightyLauncher/java/temurin_21/jdk-21.0.4+7-jre/bin/java

prepare_installation_directory wipes the target dir before each install — installs are atomic from the caller's point of view.

Locating the binary

locate_binary_in_directory handles three macOS layouts:

Layout Distribution Path
Contents/Home/bin/java Temurin <jre_root>/Contents/Home/bin/java
*.jre/Contents/Home/bin/java Zulu Java 8 on macOS nested bundle
bin/java (flat) Liberica tar.gz <jre_root>/bin/java

Linux uses bin/java; Windows uses bin/java.exe.

On Unix, ensure_executable_permissions chmods the binary to 0o755 before returning.

Example

use lighty_core::AppState;
use lighty_java::{JavaDistribution, jre_downloader};

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    AppState::init("LightyLauncher")?;
    let runtimes = AppState::cache_dir().join("java");

    let java = jre_downloader::jre_download(
        &runtimes,
        &JavaDistribution::Temurin,
        &21,
        |cur, tot| {
            if tot > 0 {
                println!("{:.1}%", cur as f64 * 100.0 / tot as f64);
            }
        },
        #[cfg(feature = "events")] None,
    ).await?;

    println!("java: {}", java.display());
    Ok(())
}

With events

Pass Some(&bus) to receive the eight JavaEvent variants. See events.md.

Errors

pub enum JreError {
    NotFound { path: PathBuf },
    InvalidStructure,
    Download(String),       // wraps provider URL fetch + download_file
    UnsupportedOS,
    Io(std::io::Error),
    Extraction(String),     // wraps zip_extract / tar_gz_extract
}

See also