How to Execute Java Code Stored in a String Variable?

Executing Code Stored in a String

Question:

Can one execute Java code that is stored within a String variable? Is it possible to convert such a String into a Java statement and run it?

Answer:

Using the Compiler API

As mentioned in a previous suggestion, the Compiler API enables you to compile and execute code dynamically. Here's how you can utilize it:

<code class="java">// Create a Java source code string
String javaCode = "...";

// Create a Java compiler instance
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

// Create a source code file from the string
JavaFileObject javaFile = new StringJavaFileObject("MyCode", javaCode);

// Compile the source code
DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<>();
Iterable<? extends JavaFileObject> compilationUnits = Collections.singletonList(javaFile);
compiler.getTask(null, null, diagnostics, null, null, compilationUnits).call();

// Execute the compiled code
Class<?> clazz = Class.forName("MyCode");
Method method = clazz.getDeclaredMethod("myMethod");
method.invoke(null);</code>

Using Beanshell

Alternatively, you can employ the Beanshell library as follows:

<code class="java">// Create a Beanshell interpreter and add the Java code to it
Interpreter interpreter = new Interpreter();
interpreter.eval(javaCode);

// Access the defined classes and methods in the interpreter
Class<?> myClass = interpreter.getClassLoader().loadClass("MyClass");
Method method = myClass.getDeclaredMethod("myMethod");
method.invoke(null);</code>

Note that Beanshell is no longer actively developed but remains reliable for production environments.

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