avoid nested if in hashmap which is created from complex json

Question

I have a hashmap which has key value pair of String and object. It is the conversion of something like below json.

{
    "test1": {
        "test2": {
            "test3": {
                "key": "value"
            },
            "somefields12": "some value2"
        },
        "somefields": "some value"
    }
}

But, I am not converting to map. I have just that map. If this may has key and value , I have to do write some logic based on that value. I implemented as below:

    if (map.containsKey("test1") ) {
        final HashMap<String, Object> test1 = (HashMap<String, Object>) map.get("test1");
        if (test1.containsKey("test2")) {
            final List<Object> test2 = (List<Object>) test1.get("test2");
            if (!test2.isEmpty()) {
                final HashMap<String, Object> test3 = (HashMap<String, Object>) test2.get(0);
                if (test3.containsKey("key")) {
                    final String value = String.valueOf(test2.get("key"));
                    if (!StringUtils.isBlank(value)) {
                        //do some work based on value
                    }
                }
            }
        }
    }

Now, I wanted to avoid the nested if (multiple ifs) from my code. What would be the best way to do so?

Answer 1

I'm not familiar with the fancy new Java 8 features, so I'd do it the old fashioned way with a function that takes a path to look up, and walks the list with a loop:

import java.util.*;

class Test {

  static String getByPath(HashMap<String, Object> map, String... path) {
    for(int i=0; i<path.length-1; i++) {
      map = (HashMap<String, Object>) map.get(path[i]);
      if (map == null) return null;
    }
    Object value = map.get(path[path.length-1]);
    return value == null ? null : String.valueOf(value);
  }

  public static void main(String[] args) {
    HashMap<String, Object> map = new HashMap<>();
    HashMap<String, Object> tmp1 = new HashMap<>();
    HashMap<String, Object> tmp2 = new HashMap<>();
    map.put("test1", tmp1);
    tmp1.put("test2", tmp2);
    tmp2.put("key1", "My Value");

    System.out.println("With valid path:   " + getByPath(map, "test1", "test2", "key1"));
    System.out.println("With invalid path: " + getByPath(map, "test1", "BANANA", "key1"));
  }
}

This results in:

With valid path:   My Value
With invalid path: null

This can optionally be extended to:

• Check that nodes are in fact maps before casting
• Use Optional or a helpful exception instead of returning null