JSONからJavaクラス変換

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import java.util.List;

@JsonIgnoreProperties(ignoreUnknown = true)
public class User {
    private int id;
    private String name;
    private String email;
    private boolean active;
    private double score;
    private Address address;
    private List<String> tags;

    // getters and setters omitted for brevity

    public static void main(String[] args) throws Exception {
        String json = "{\"id\":1,\"name\":\"Alice\",\"email\":\"alice@example.com\",\"active\":true,\"score\":98.5,\"address\":{\"street\":\"123 Main St\",\"city\":\"Springfield\",\"zip\":\"12345\"},\"tags\":[\"admin\",\"user\"]}";
        ObjectMapper mapper = new ObjectMapper();
        User user = mapper.readValue(json, User.class);
        System.out.println(user.getName()); // -> Alice
    }
}

class Address {
    private String street;
    private String city;
    private String zip;
    // getters and setters
}

// Minimal JSON-to-Java-POJO generator in JS
function jsonToJava(obj, name = "Root") {
  const classes = [];
  function infer(val, fieldName) {
    if (val === null) return "Object";
    if (typeof val === "string") return "String";
    if (typeof val === "number") return Number.isInteger(val) ? "int" : "double";
    if (typeof val === "boolean") return "boolean";
    if (Array.isArray(val)) {
      const first = val.find(v => v !== null);
      if (!first) return "List<Object>";
      const elem = infer(first, fieldName);
      const boxed = elem === "int" ? "Integer" : elem === "double" ? "Double" : elem === "boolean" ? "Boolean" : elem;
      return `List<${boxed}>`;
    }
    if (typeof val === "object") {
      const cls = fieldName.charAt(0).toUpperCase() + fieldName.slice(1);
      build(val, cls);
      return cls;
    }
    return "Object";
  }
  function build(obj, cls) {
    const fields = Object.entries(obj).map(([k, v]) => {
      const type = infer(v, k);
      return `    private ${type} ${k};`;
    });
    classes.push(`public class ${cls} {\n${fields.join("\n")}\n}`);
  }
  build(obj, name);
  return classes.join("\n\n");
}

console.log(jsonToJava({ id: 1, name: "Alice", scores: [98, 85] }, "User"));
// public class User {
//     private int id;
//     private String name;
//     private List<Integer> scores;
// }

import json

def json_to_java(obj: dict, class_name: str = "Root") -> str:
    classes = []

    def infer(val, name):
        if val is None:
            return "Object"
        if isinstance(val, bool):
            return "boolean"
        if isinstance(val, int):
            return "int"
        if isinstance(val, float):
            return "double"
        if isinstance(val, str):
            return "String"
        if isinstance(val, list):
            if not val:
                return "List<Object>"
            elem = infer(val[0], name)
            boxed = {"int": "Integer", "double": "Double", "boolean": "Boolean"}.get(elem, elem)
            return f"List<{boxed}>"
        if isinstance(val, dict):
            cls = name[0].upper() + name[1:]
            build(val, cls)
            return cls
        return "Object"

    def build(obj, cls):
        fields = [f"    private {infer(v, k)} {k};" for k, v in obj.items()]
        classes.append(f"public class {cls} {{\n" + "\n".join(fields) + "\n}")

    build(obj, class_name)
    return "\n\n".join(classes)

data = json.loads('{"id": 1, "name": "Alice", "tags": ["admin"]}')
print(json_to_java(data, "User"))
# public class User {
#     private int id;
#     private String name;
#     private List<String> tags;
# }

# Install jsonschema2pojo (requires Java 8+)
# Download from https://github.com/joelittlejohn/jsonschema2pojo

# Generate POJOs from a JSON file
jsonschema2pojo --source user.json --target src/main/java \
  --source-type json --annotation-style jackson2

# Generate with Gson annotations instead
jsonschema2pojo --source user.json --target src/main/java \
  --source-type json --annotation-style gson

# From a JSON string via stdin
echo '{"id": 1, "name": "Alice", "tags": ["admin"]}' | \
  jsonschema2pojo --source-type json --annotation-style jackson2 \
  --target src/main/java --target-package com.example.model