Java implementation method for dynamically generating byte code from a string _java

can generate an executable class file

Can execute code directly:

Copy Code code as follows:

public class Test {

/**
* @param args
*/
@SuppressWarnings ("Static-access")
public static void Main (string[] args) {
try {
New Test (). Calculate ("234-(1 + 45 * 4)/5");
catch (Exception e) {
E.printstacktrace ();
}
}

Private static double calculate (String expr) throws Exception {
  string className = "Calculatormain";
  String methodname = "Calculate";
  String Source = "Class" + className
    + "{public static void main (string[] args) {System. Out.println (Calculate ());} public static Double "+ methodname +" () {return "
    + expr +;}}";
  Javacompiler compiler = Toolprovider.getsystemjavacompiler ();
  Standardjavafilemanager FileManager = Compiler.getstandardfilemanager (
    null, NULL, NULL);
  Stringsourcejavaobject sourceObject = new Test.stringsourcejavaobject (
    "Main", SOURCE);
  iterable< extends javafileobject> fileobjects = Arrays
   . aslist (sourceObject);
  Compilationtask task = Compiler.gettask (null, filemanager, NULL, NULL,
    null, fileobjects);

Boolean result = Task.call ();
if (result) {
ClassLoader loader = Thread.CurrentThread (). GetClass ()
. getClassLoader ();
try {
Class<?> clazz = Loader.loadclass (className);
Method method = Clazz.getmethod (methodname, new class<?>[] {});
Object value = Method.invoke (null, new object[] {});
Return (Double) value;
catch (Exception e) {
throw new Calculationexception ("Internal error.") ");
}
} else {
/New Calculationexception ("Wrong expression"). ");
}
return 0;
}

Static Class Stringsourcejavaobject extends Simplejavafileobject {

Private String content = null;

Public Stringsourcejavaobject (string name, string content)
Throws URISyntaxException {
Super (Uri.create ("string:///" + name.replace ('. ', '/')
+ Kind.SOURCE.extension), kind.source);
this.content = content;
}

Public Charsequence getcharcontent (Boolean ignoreencodingerrors)
Throws IOException {
return content;
}
}

}