Spark Java : Before and After filters

Before filters are evaluated before each request and can read the request and read/modify the response.

After filters are evaluated after each request and can read the request and read/modify the response.

import static spark.Spark.*;

public class HelloSpark {
 public static void main(String[] args) { 
  
  before((request, response) -> {
     System.out.println("I am in before filter");
  });
  
  get("/hello", (request, response) -> { 
   System.out.println("I am processing");
     return "Hello";
  });
  
  after((request, response) -> {
      System.out.println("I am in after filter");
  });
 }

}

http://localhost:4567/hello

Hit above URL, you will get below messages in console.

I am in before filter

I am processing

I am in after filter

Filters optionally take a pattern, causing them to be evaluated only if the request path matches that pattern.

before("/hi", (request, response) -> {
 System.out.println("Filter for request hi");
});

Above filter evaluates, if request url is "/hi" (you can add wildcards to url).

import static spark.Spark.*;

public class HelloSpark {
 public static void main(String[] args) { 
  
  before((request, response) -> {
     System.out.println("I am in before filter");
  });
  
  get("/hello", (request, response) -> { 
   System.out.println("I am processing hello request");
     return "Hello";
  });
  
  after((request, response) -> {
      System.out.println("I am in after filter");
  });
  
  before("/hi", (request, response) -> {
   System.out.println("Filter for request hi");
  });
  
  get("/hi", (request, response) -> { 
   System.out.println("I am processing hi request");
     return "Hi";
  });
 }

}

Hit URLs

http://localhost:4567/hello

http://localhost:4567/hi

You will get messages like below in console.

I am in before filter

I am processing hello request

I am in after filter

I am in before filter

Filter for request hi

I am processing hi request

I am in after filter

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