Call external javascript functions from java code
Solution 1:
Use ScriptEngine.eval(java.io.Reader)
to read the script
ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("JavaScript");
// read script file
engine.eval(Files.newBufferedReader(Paths.get("C:/Scripts/Jsfunctions.js"), StandardCharsets.UTF_8));
Invocable inv = (Invocable) engine;
// call function from script file
inv.invokeFunction("yourFunction", "param");
Solution 2:
try {
ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("JavaScript");
System.out.println("okay1");
FileInputStream fileInputStream = new FileInputStream("C:/Users/Kushan/eclipse-workspace/sureson.lk/src/main/webapp/js/back_end_response.js");
System.out.println("okay2");
if (fileInputStream != null){
BufferedReader reader = new BufferedReader(new InputStreamReader(fileInputStream));
engine.eval(reader);
System.out.println("okay3");
// Invocable javascriptEngine = null;
System.out.println("okay4");
Invocable invocableEngine = (Invocable)engine;
System.out.println("okay5");
int x=0;
System.out.println("invocableEngine is : "+invocableEngine);
Object object = invocableEngine.invokeFunction("backend_message",x);
System.out.println("okay6");
}
}catch(Exception e) {
System.out.println("erroe when calling js function"+ e);
}
Solution 3:
Let us say your jsfunctions.js file has a function "display" and this file is stored in C:/Scripts/Jsfunctions.js
jsfunctions.js
var display = function(name) {
print("Hello, I am a Javascript display function",name);
return "display function return"
}
Now, in your java code, I would recommend you to use Java8 Nashorn. In your java class,
import java.io.FileNotFoundException;
import java.io.FileReader;
import javax.script.Invocable;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
class Test {
public void runDisplay() {
ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
try {
engine.eval(new FileReader("C:/Scripts/Jsfunctions.js"));
Invocable invocable = (Invocable) engine;
Object result;
result = invocable.invokeFunction("display", helloWorld);
System.out.println(result);
System.out.println(result.getClass());
} catch (FileNotFoundException | NoSuchMethodException | ScriptException e) {
e.printStackTrace();
}
}
}
Note: Get the absolute path of your javascript file and replace in FileReader() and run the java code. It should work.