Validate Java Expression

    You may come under a scenario where you want to check at runtime if the given expression is valid or not. For example you are building a expression builder on the client side. With the help of of expression builder you can create a expression. Expression may contains different data types like Integer, String and Date. Now the question is how can any one check if the build expression is valid or not. I have the following code that will ensure given expression is valid or not.

Assumption :

1) This code will work on java 6 and above.

2) You have to pass the expression in the form of values.

import java.io.PrintWriter; import java.io.StringWriter; import java.net.URI; import java.util.Arrays; import javax.tools.DiagnosticCollector; import javax.tools.JavaCompiler; import javax.tools.JavaFileObject; import javax.tools.SimpleJavaFileObject; import javax.tools.ToolProvider; import javax.tools.JavaCompiler.CompilationTask; public class ExpressionEvaluator { public static boolean isValidExpression( String expression) { JavaCompiler compiler = ToolProvider.getSystemJavaCompiler(); System.out.println("compiler  = " + compiler); System.out.println("JAVA HOME = " + System.getProperty("java.home")); System.out.println("CLASSPATH = " + System.getProperty("java.class.path")); DiagnosticCollector<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>(); StringWriter writer = new StringWriter(); PrintWriter out = new PrintWriter(writer); out.println("public class TextExpression {"); out.println("  public static void main(String args[]) {"); out.println("    if(" + expression + "){}"); out.println("  }"); out.println("}"); out.close(); JavaFileObject file = new JavaSourceFromString("TextExpression", writer.toString()); Iterable<? extends JavaFileObject> compilationUnits = Arrays.asList(file); CompilationTask task = compiler.getTask(null, null, diagnostics, null, null, compilationUnits); boolean success = task.call(); return success; } } class JavaSourceFromString extends SimpleJavaFileObject { final String code; JavaSourceFromString(String name, String code) { super(URI.create("string:///" + name.replace('.', '/')+ Kind.SOURCE.extension), Kind.SOURCE); this.code = code; } @Override public CharSequence getCharContent(boolean ignoreEncodingErrors) { return code; } }