Runtime.exec() vs. ProcessBuilder.start(): When Should I Use Each?

ProcessBuilder vs. Runtime.exec(): Understanding the Difference

When attempting to execute external commands from Java, developers often encounter a discrepancy in behavior between Runtime.exec() and ProcessBuilder.start().

Runtime.exec():

Using Runtime.getRuntime().exec() involves a two-step process: tokenization and execution. The input string is parsed and converted into an array of arguments before being executed.

ProcessBuilder:

In contrast, ProcessBuilder operates differently. Its constructors accept a varargs array or a list of strings, where each string represents an individual argument. The arguments are then combined into a single string that is passed to the operating system.

Impact on Execution:

This difference in argument handling can impact the execution of the command. For instance, if the command includes spaces, Runtime.exec() will automatically handle the tokenization, whereas ProcessBuilder requires explicitly creating the argument array or list.

Example:

Consider the following command with spaces:

"C:\DoStuff.exe -arg1 -arg2"

Using Runtime.exec():

Process p = Runtime.getRuntime().exec("C:\DoStuff.exe -arg1 -arg2");

In this case, the command will be executed as intended, and the exitValue will be 0.

Using ProcessBuilder:

Process p = (new ProcessBuilder("C:\DoStuff.exe -arg1 -arg2")).start();

However, using ProcessBuilder directly without tokenization will result in an error or unexpected behavior, returning an exitValue of 1001. To correct this, you must create the argument array explicitly:

Process p = (new ProcessBuilder("C:\DoStuff.exe", "-arg1", "-arg2")).start();

Summary:

In general, when using ProcessBuilder, it's essential to provide the arguments as a separate list or array, explicitly indicating each individual argument. This additional step ensures that the arguments are parsed correctly and the external command is executed as intended.

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