Error: DynamoDB Mapper Could Not Instantiate Class

This Java DynamoDBMapper error means the mapper could not construct your model while reading an item. Check the nested exception for a missing public no-argument constructor, an abstract class, a non-static inner class, or a constructor that throws. Changing save behavior does not fix object construction.

1. Make the mapped class public and concrete. Add a public constructor with no arguments if you also define parameterized constructors.
2. If the model is nested, make it static or move it to a top-level class. Check the same requirements for mapped document classes.
3. Check getters, setters, and the key annotations; keep constructors free of initialization that can fail during deserialization.

Use the current Java mapping API

DynamoDBMapper belongs to AWS SDK for Java 1.x, which has reached end of support. With Java 2.x, use the Enhanced Client. This bean works with TableSchema.fromBean(Order.class):

import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbBean;
import software.amazon.awssdk.enhanced.dynamodb.mapper.annotations.DynamoDbPartitionKey;

@DynamoDbBean
public class Order {
    private String id;
    public Order() {}
    @DynamoDbPartitionKey
    public String getId() { return id; }
    public void setId(String id) { this.id = id; }
}

For an intentionally immutable model, use the Enhanced Client’s immutable mapping or an explicit schema instead of forcing a mutable bean. Do not mix v1 mapper annotations with v2 annotations.

See Java mapping examples and AWS documentation.