Eclipse – Ant build won’t run in Eclipse

You can build an eclipse project via a workspace from the command line:

eclipsec.exe -noSplash -data "D:\Source\MyProject\workspace" -application org.eclipse.jdt.apt.core.aptBuild

It uses the jdt apt plugin to build your workspace automatically. This is also known as a 'Headless Build'. Damn hard to figure out. If you're not using a win32 exe, you can try this:

java -cp startup.jar -noSplash -data "D:\Source\MyProject\workspace" -application org.eclipse.jdt.apt.core.aptBuild

Update

Several years ago eclipse replaced startup.jar with the "equinox launcher"

https://wiki.eclipse.org/Equinox_Launcher

On Eclipse Mars (MacOX):

java -jar /Applications/Eclipse.app/Contents/Eclipse/plugins/org.eclipse.equinox.launcher_1.3.100.v20150511-1540.jar -noSplash -data "workspace" -application org.eclipse.jdt.apt.core.aptBuild

The -data parameter specifies the location of your workspace.

The version number for the equinox launcher will depend on what version of eclipse you have.

The three most influential factors for Eclipse speed are:

• Using the latest version of Eclipse (2020-06 as on 26 June 2020)
  Note that David Balažic's comment (July 2014) contradicts that criteria which was working six years ago:

The "same" workspace in Indigo (3.7.2) SR2 loads in 4 seconds, in Kepler SR2 (4.3.2) in 7 seconds and in Luna (4.4.0) in 10 seconds. All are Java EE bundles. Newer versions have more bundled plugins, but still the trend is obvious. (by "same" workspace I mean: same (additionally installed) plugins used, same projects checked out from version control).

• Launching it with the latest JDK (Java 14 at the time of writing, which does not prevent you to compile in your Eclipse project with any other JDK you want: 1.4.2, 1.5, 1.6 older...)

    -vm jdk1.6.0_10\jre\bin\client\jvm.dll
  

• Configuring the eclipse.ini (see this question for a complete eclipse.ini)

    -Xms512m
    -Xmx4096m
    [...]
  

The Xmx argument is the amount of memory Eclipse will get (in simple terms). With -Xmx4g, it gets 4 GB of RAM, etc.

Note:

1. Referring to the jvm.dll has advantages:

• Splash screen coming up sooner.
• Eclipse.exe in the process list instead of java.exe.
• Firewalls: Eclipse wants access to the Internet instead of Java.
• Window management branding issues, especially on Windows and Mac.

Dec. 2020, Udo conforms in the comments

From version 4.8 (Photon) an up there was a steady speed gain after each version.
The main platform was optimized every release to load faster, enable more features for the dark theme and to add more features for newer Java versions for the Java development tools.
Especially with-in the last 3 versions the startup time was increased a lot. There should be a significant increase in start-up time with the newest version of Eclipse 2020-12.

In my experience it started a lot faster with each new version.
But: There are still plug-ins which do not follow the new way of using the Eclipse API and are therefore still slow to start.
Since the change to Java 11 as the minimum runtime version starting from Eclipse version 2020-09 at least the core system uses the newer features of the JVM. It is up to the providers of the other plug-ins to upgrade to newer APIs and to use the full power of modern CPUs (e.g. concurrent programming model).