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Showing content from https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/ddb-en-client-gs-tableschema.html below:

Generate a TableSchema from a data class

A TableSchema enables the enhanced client to map DynamoDB attribute values to and from your client-side classes. In this tutorial, you learn about TableSchemas derived from a static data class and generated from code by using a builder.

The SDK for Java 2.x includes a set of annotations that you can use with a data class to quickly generate a TableSchema for mapping your classes to tables.

Start by creating a data class that conforms to the JavaBean specification. The specification requires that a class has a no-argument public constructor and has getters and setters for each attribute in the class. Include a class-level annotation to indicate that the data class is a DynamoDbBean. Also, at a minimum, include a DynamoDbPartitionKey annotation on the getter or setter for the primary key attribute.

You can apply attribute-level annotations to getters or setters, but not both.

The term property is normally used for a value encapsulated in a JavaBean. However, this guide uses the term attribute instead, to be consistent with the terminology used by DynamoDB.

The following Customer class shows annotations that link the class definition to a DynamoDB table.

package org.example.tests.model;

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

import java.time.Instant;

@DynamoDbBean
public class Customer {

    private String id;
    private String name;
    private String email;
    private Instant regDate;

    @DynamoDbPartitionKey
    public String getId() { return this.id; }

    public void setId(String id) { this.id = id; }

    public String getCustName() { return this.name; }

    public void setCustName(String name) { this.name = name; }

    @DynamoDbSortKey
    public String getEmail() { return this.email; }

    public void setEmail(String email) { this.email = email; }

    public Instant getRegistrationDate() { return this.regDate; }

    public void setRegistrationDate(Instant registrationDate) { this.regDate = registrationDate; }

    @Override
    public String toString() {
        return "Customer [id=" + id + ", name=" + name + ", email=" + email
                + ", regDate=" + regDate + "]";
    }
}

After you have created an annotated data class, use it to create the TableSchema, as shown in the following snippet.

static final TableSchema<Customer> customerTableSchema = TableSchema.fromBean(Customer.class);

A TableSchema is designed to be static and immutable. You can usually instantiate it at class-load time.

The static TableSchema.fromBean() factory method introspects the bean to generate the mapping of data class attributes (properties) to and from DynamoDB attributes.

For an example of working with a data model made up of several data classes, see the Person class in the Work with attributes that are beans, maps, lists and sets section.

You can skip the cost of bean introspection if you define the table schema in code. If you code the schema, your class does not need to follow JavaBean naming standards nor does it need to be annotated. The following example uses a builder and is equivalent to the Customer class example that uses annotations.

static final TableSchema<Customer> customerTableSchema =
                TableSchema.builder(Customer.class)
                        .newItemSupplier(Customer::new)
                        .addAttribute(String.class, a -> a.name("id")
                                .getter(Customer::getId)
                                .setter(Customer::setId)
                                .tags(StaticAttributeTags.primaryPartitionKey()))
                        .addAttribute(String.class, a -> a.name("email")
                                .getter(Customer::getEmail)
                                .setter(Customer::setEmail)
                                .tags(StaticAttributeTags.primarySortKey()))
                        .addAttribute(String.class, a -> a.name("name")
                                .getter(Customer::getCustName)
                                .setter(Customer::setCustName))
                        .addAttribute(Instant.class, a -> a.name("registrationDate")
                                .getter(Customer::getRegistrationDate)
                                .setter(Customer::setRegistrationDate))
                        .build();

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