> Markdown version of [Requirements and Configuration](https://vaadin.com/docs/v25/tools/modernization-toolkit/swing-bridge/netbeans-rcp/configuration). Section index: [llms.txt](https://vaadin.com/docs/v25/tools/llms.txt)

# <a id="swing-bridge.netbeans-rcp.configuration"></a>Requirements and Configuration

This page covers what a NetBeans Platform guest needs on top of a standard SwingBridge setup: how the distribution is discovered, the additional JVM flags, and the system properties that control embedding.

## <a id="swing-bridge.netbeans-rcp.configuration.requirements"></a>Requirements

- **A pre-built NetBeans Platform distribution** — the directory the platform’s own launcher would run. It must contain at least `etc/<branding>.clusters` and `platform/lib/boot.jar`, alongside the branding cluster and the feature module clusters. Bare `.nbm` files without a host application are not supported.

- **JDK 21.** NetBeans Platform 25’s `TopSecurityManager` depends on classes removed in JDK 24 and later; embedding on a newer JDK requires a NetBeans Platform variant that has dropped that dependency.

- **The standard SwingBridge runtime setup** — the `--patch-module` / `-Xbootclasspath/a` flags, `java.awt.headless=false`, a valid license, and server push (`@Push`). See [Installation from Scratch](https://vaadin.com/docs/v25/tools/modernization-toolkit/swing-bridge/installation-from-scratch.md).

## <a id="swing-bridge.netbeans-rcp.configuration.discovery"></a>Cluster Discovery

SwingBridge locates the NetBeans Platform distribution using the same convention ladder plain Swing guests use for their JARs. The first source that yields a valid distribution wins:

| Order | Source                                          | Notes                                                                                                                                                                                                                                                                                                       |
| ----- | ----------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| 1     | `-Dswingbridge.rcp.cluster.dir=<absolute-path>` | Explicit override. Useful for power users and CI.                                                                                                                                                                                                                                                           |
| 2     | Directory entries in `swing-app-jar-list.conf`  | The same file plain Swing guests use. Entries that are **directories** (not JARs) are treated as candidate distributions. See [Using `swing-app-jar-list.conf`](https://vaadin.com/docs/v25/tools/modernization-toolkit/swing-bridge/adding-your-app.md#swing-bridge.adding-your-app.jar-loading.jar-list). |
| 3     | The `applibs/` directory                        | Resolved exactly as for plain Swing guests (`-Dapplibs.dir` → next to the running JAR → `<user.dir>/applibs`). The directory itself and one level below it are probed, since some build outputs nest the distribution under a versioned subdirectory.                                                       |

A directory qualifies as a distribution only when it contains **both** `etc/<branding>.clusters` and `platform/lib/boot.jar`; the branding token is the basename of the `.clusters` file. If no source yields a valid distribution, startup fails with a message that names all three sources, so you know which levers are available. Discovery runs once per JVM and the result is reused across sessions.

> **Note:** A frequent mistake is listing the distribution’s individual JARs in `swing-app-jar-list.conf`. Cluster discovery only recognizes **directory** entries — add the distribution’s root directory, not its JARs.

## <a id="swing-bridge.netbeans-rcp.configuration.jvm-flags"></a>NetBeans JVM Flags

A NetBeans Platform guest needs a few JVM flags beyond the standard SwingBridge runtime set documented in [JVM Flags Reference](https://vaadin.com/docs/v25/tools/modernization-toolkit/swing-bridge/installation-from-scratch.md#swing-bridge.installation-from-scratch.jvm-flags). Add these to the `<jvmArguments>` of the `spring-boot-maven-plugin`, together with the standard set:

```
--add-opens=java.base/java.lang=ALL-UNNAMED
--add-opens=java.desktop/javax.swing=ALL-UNNAMED
--add-opens=java.desktop/javax.swing.text=ALL-UNNAMED
--add-opens=java.base/java.net=ALL-UNNAMED
--add-opens=java.base/java.security=ALL-UNNAMED
-Djava.security.manager=allow
```

| Flag                                                                                                       | Purpose                                                                                                                                                                                                                                          |
| ---------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `--add-opens=java.base/java.lang=ALL-UNNAMED`                                                              | **Required.** Lets SwingBridge give each tenant a thread group that reports itself as a JVM root, so NetBeans’s `RequestProcessor` attributes its worker threads per tenant. Without it, platform startup fails with a message naming this flag. |
| `-Djava.security.manager=allow`                                                                            | **Required.** NetBeans Platform 25 installs a `SecurityManager` during boot. On JDK 21 this is only permitted when the JVM is started with `-Djava.security.manager=allow`.                                                                      |
| `--add-opens=java.desktop/javax.swing=ALL-UNNAMED` `--add-opens=java.desktop/javax.swing.text=ALL-UNNAMED` | Reflective access the platform performs into Swing internals during boot and rendering.                                                                                                                                                          |
| `--add-opens=java.base/java.net=ALL-UNNAMED` `--add-opens=java.base/java.security=ALL-UNNAMED`             | Reflective access the platform’s module system and networking layers perform during boot.                                                                                                                                                        |

> **Important:** These flags apply to the runtime JVM only. The compile-time `.mvn/jvm.config` set from [Project Setup](https://vaadin.com/docs/v25/tools/modernization-toolkit/swing-bridge/installation-from-scratch.md#swing-bridge.installation-from-scratch.project-setup) is unchanged — the additional flags above are not needed to compile.

## <a id="swing-bridge.netbeans-rcp.configuration.system-properties"></a>System Properties

In addition to the SwingBridge system properties (see [System Properties Reference](https://vaadin.com/docs/v25/tools/modernization-toolkit/swing-bridge/configuration.md#swing-bridge.configuration.system-properties)), the following applies to NetBeans Platform guests:

| Property                      | Default | Description                                                                                                                                                                  |
| ----------------------------- | ------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `swingbridge.rcp.cluster.dir` | —       | Absolute path to the NetBeans Platform distribution directory. Highest-priority discovery source; overrides `swing-app-jar-list.conf` entries and the `applibs/` convention. |

The per-tenant `--userdir`, `--cachedir`, `--branding`, and look-and-feel arguments are derived and managed automatically per session; they are not configured by hand.

## <a id="swing-bridge.netbeans-rcp.configuration.laf"></a>Look and Feel

The bridge resolves the look-and-feel from the distribution’s `etc/<branding>.conf` file — the `--laf <class>` token in its `default_options` line — and falls back to `com.formdev.flatlaf.FlatLightLaf` when the file is missing or specifies no look-and-feel. Because each session’s frames are rendered into an HTML canvas with no native window, the bridge also transparently handles two platform-default behaviors that don’t apply to offscreen rendering: it keeps the main menu bar painted in-window on macOS, and it disables FlatLaf’s native window library on Windows. No configuration is required for either.