I'm trying to create a pojo from a json file. But, for some reason "node.get("name").asText()" returns null.
The error happens at line 8 and here's what the debugger throws.
java.lang.NullPointerException: Cannot invoke "com.fasterxml.jackson.databind.JsonNode.asText()" because the return value of "com.fasterxml.jackson.databind.JsonNode.get(String)" is null.
I've already tried "node.get("solution").get("name").asText()" and switching "asText()" to "toString()", the result was the same.
Code fragment:
public static solution findSolution(String name){
File file = new File("/home/clementino/IdeaProjects/helloworldJava/problems.json");
ObjectMapper mapper = new ObjectMapper();
solution solution = new solution();
try {
JsonNode tree = mapper.readTree(file);
for(JsonNode node : tree){
if(node.get("name").asText().equalsIgnoreCase(name)){ //problema
solution = mapper.treeToValue(node, solution.class);
System.out.println(solution.getName());
}else{
System.out.println("problem doesnt exist");
}
}
}catch(Exception e){
System.out.println("error");
}
return solution;
}
problems.json:
{
"solution": [
{
"name":"twoSum",
"difficulty": "easy",
"status": "time exceeded",
"lastModified": "12-05-2025",
"testCase": false,
"source": "leetcode.com",
"language": "java"
},
{
"name": "Watermelon",
"difficulty": "easy",
"status": "working",
"lastModified": "05-02-2024",
"testCase": false,
"source": "codeforces.com",
"language": "C++"
}
]
}Answer
could you try this code?
JsonNode tree = mapper.readTree(file);
JsonNode solutionsArray = tree.get("solution");
if (solutionsArray != null && solutionsArray.isArray()) {
for (JsonNode node : solutionsArray) {
if (node.get("name") != null && node.get("name").asText().equalsIgnoreCase(name)) {
solution = mapper.treeToValue(node, solution.class);
System.out.println(solution.getName());
} else {
System.out.println("problem doesn't exist");
}
}
}
I think the issue is that you're trying to iterate over the root JsonNode, but your JSON structure wraps the actual array inside a solution field. Therefore, tree is not an array, and calling .get("name") on it will return null, causing the NullPointerException.