Resolving the "Failed to Bounce to Type" Error When Converting Firebase JSON to Java Objects

Why do I encounter a 'Failed to bounce to type' error when converting Firebase JSON data into Java objects?

// Example Java model class
public class User {
    private String id;
    private String name;
    private int age;
    
    // Constructors, getters and setters
}

The 'Failed to bounce to type' error typically arises during the deserialization process when you attempt to convert JSON data from Firebase into Java objects. This issue often stems from mismatched data types or missing fields that prevent the JSON parser from accurately mapping the data to the Java model classes.

import com.fasterxml.jackson.annotation.JsonProperty;

public class User {
    private String id;
    private String name;
    private Integer age; // Use Integer instead of int to allow null
    
    // Default constructor
    public User() {}
    
    // Getters and setters
    public String getId() { return id; }
    public void setId(String id) { this.id = id; }
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public Integer getAge() { return age; }
    public void setAge(Integer age) { this.age = age; }
}

Causes

• Mismatched data types between JSON and Java fields.
• Missing default constructors in Java classes.
• Improperly named fields that do not align with JSON keys.
• Nullable fields mapped to primitive types.

Solutions

• Ensure that your Java fields have the correct data type matching the JSON.
• Make sure every Java model class has a default (no-argument) constructor.
• Use annotations like @JsonProperty to map JSON keys to differently named Java fields.
• Convert primitive data types to their corresponding wrapper classes to handle null values.

Mistake: Not including a default constructor in Java classes.

Solution: Add an empty constructor to your Java model class.

Mistake: Using primitive types (e.g., int, double) without nullable wrappers.

Solution: Change primitive types to their wrapper classes (e.g., Integer, Double).

Mistake: Incorrectly named fields that don’t match the JSON keys.

Solution: Verify that Java field names match the JSON keys or use @JsonProperty to map them correctly.