Esempio: CRUD operazioni che utilizzano il documento AWS SDK for Java API

Il seguente esempio di codice illustra CRUD le operazioni su un elemento Amazon DynamoDB. L'esempio consente di creare un item, recuperarlo, eseguire vari aggiornamenti e infine eliminare l'item.

Nota

The SDK for Java fornisce anche un modello di persistenza degli oggetti, che consente di mappare le classi lato client alle tabelle DynamoDB. Questo approccio può ridurre la quantità di codice da scrivere. Per ulteriori informazioni, consulta Java 1.x: D ynamoDBMapper.

Nota

In questo esempio di codice si presuppone che i dati siano già stati caricati in DynamoDB per l'account seguendo le istruzioni riportate nella sezione Creazione di tabelle e caricamento di dati per esempi di codice in DynamoDB.

Per step-by-step istruzioni su come eseguire l'esempio seguente, consulta. Esempi di codice Java

package com.amazonaws.codesamples.document;

import java.io.IOException;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.document.DeleteItemOutcome;
import com.amazonaws.services.dynamodbv2.document.DynamoDB;
import com.amazonaws.services.dynamodbv2.document.Item;
import com.amazonaws.services.dynamodbv2.document.Table;
import com.amazonaws.services.dynamodbv2.document.UpdateItemOutcome;
import com.amazonaws.services.dynamodbv2.document.spec.DeleteItemSpec;
import com.amazonaws.services.dynamodbv2.document.spec.UpdateItemSpec;
import com.amazonaws.services.dynamodbv2.document.utils.NameMap;
import com.amazonaws.services.dynamodbv2.document.utils.ValueMap;
import com.amazonaws.services.dynamodbv2.model.ReturnValue;

public class DocumentAPIItemCRUDExample {

    static AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();
    static DynamoDB dynamoDB = new DynamoDB(client);

    static String tableName = "ProductCatalog";

    public static void main(String[] args) throws IOException {

        createItems();

        retrieveItem();

        // Perform various updates.
        updateMultipleAttributes();
        updateAddNewAttribute();
        updateExistingAttributeConditionally();

        // Delete the item.
        deleteItem();

    }

    private static void createItems() {

        Table table = dynamoDB.getTable(tableName);
        try {

            Item item = new Item().withPrimaryKey("Id", 120).withString("Title", "Book 120 Title")
                    .withString("ISBN", "120-1111111111")
                    .withStringSet("Authors", new HashSet<String>(Arrays.asList("Author12", "Author22")))
                    .withNumber("Price", 20).withString("Dimensions", "8.5x11.0x.75").withNumber("PageCount", 500)
                    .withBoolean("InPublication", false).withString("ProductCategory", "Book");
            table.putItem(item);

            item = new Item().withPrimaryKey("Id", 121).withString("Title", "Book 121 Title")
                    .withString("ISBN", "121-1111111111")
                    .withStringSet("Authors", new HashSet<String>(Arrays.asList("Author21", "Author 22")))
                    .withNumber("Price", 20).withString("Dimensions", "8.5x11.0x.75").withNumber("PageCount", 500)
                    .withBoolean("InPublication", true).withString("ProductCategory", "Book");
            table.putItem(item);

        } catch (Exception e) {
            System.err.println("Create items failed.");
            System.err.println(e.getMessage());

        }
    }

    private static void retrieveItem() {
        Table table = dynamoDB.getTable(tableName);

        try {

            Item item = table.getItem("Id", 120, "Id, ISBN, Title, Authors", null);

            System.out.println("Printing item after retrieving it....");
            System.out.println(item.toJSONPretty());

        } catch (Exception e) {
            System.err.println("GetItem failed.");
            System.err.println(e.getMessage());
        }

    }

    private static void updateAddNewAttribute() {
        Table table = dynamoDB.getTable(tableName);

        try {

            UpdateItemSpec updateItemSpec = new UpdateItemSpec().withPrimaryKey("Id", 121)
                    .withUpdateExpression("set #na = :val1").withNameMap(new NameMap().with("#na", "NewAttribute"))
                    .withValueMap(new ValueMap().withString(":val1", "Some value"))
                    .withReturnValues(ReturnValue.ALL_NEW);

            UpdateItemOutcome outcome = table.updateItem(updateItemSpec);

            // Check the response.
            System.out.println("Printing item after adding new attribute...");
            System.out.println(outcome.getItem().toJSONPretty());

        } catch (Exception e) {
            System.err.println("Failed to add new attribute in " + tableName);
            System.err.println(e.getMessage());
        }
    }

    private static void updateMultipleAttributes() {

        Table table = dynamoDB.getTable(tableName);

        try {

            UpdateItemSpec updateItemSpec = new UpdateItemSpec().withPrimaryKey("Id", 120)
                    .withUpdateExpression("add #a :val1 set #na=:val2")
                    .withNameMap(new NameMap().with("#a", "Authors").with("#na", "NewAttribute"))
                    .withValueMap(
                            new ValueMap().withStringSet(":val1", "Author YY", "Author ZZ").withString(":val2",
                                    "someValue"))
                    .withReturnValues(ReturnValue.ALL_NEW);

            UpdateItemOutcome outcome = table.updateItem(updateItemSpec);

            // Check the response.
            System.out.println("Printing item after multiple attribute update...");
            System.out.println(outcome.getItem().toJSONPretty());

        } catch (Exception e) {
            System.err.println("Failed to update multiple attributes in " + tableName);
            System.err.println(e.getMessage());

        }
    }

    private static void updateExistingAttributeConditionally() {

        Table table = dynamoDB.getTable(tableName);

        try {

            // Specify the desired price (25.00) and also the condition (price =
            // 20.00)

            UpdateItemSpec updateItemSpec = new UpdateItemSpec().withPrimaryKey("Id", 120)
                    .withReturnValues(ReturnValue.ALL_NEW).withUpdateExpression("set #p = :val1")
                    .withConditionExpression("#p = :val2").withNameMap(new NameMap().with("#p", "Price"))
                    .withValueMap(new ValueMap().withNumber(":val1", 25).withNumber(":val2", 20));

            UpdateItemOutcome outcome = table.updateItem(updateItemSpec);

            // Check the response.
            System.out.println("Printing item after conditional update to new attribute...");
            System.out.println(outcome.getItem().toJSONPretty());

        } catch (Exception e) {
            System.err.println("Error updating item in " + tableName);
            System.err.println(e.getMessage());
        }
    }

    private static void deleteItem() {

        Table table = dynamoDB.getTable(tableName);

        try {

            DeleteItemSpec deleteItemSpec = new DeleteItemSpec().withPrimaryKey("Id", 120)
                    .withConditionExpression("#ip = :val").withNameMap(new NameMap().with("#ip", "InPublication"))
                    .withValueMap(new ValueMap().withBoolean(":val", false)).withReturnValues(ReturnValue.ALL_OLD);

            DeleteItemOutcome outcome = table.deleteItem(deleteItemSpec);

            // Check the response.
            System.out.println("Printing item that was deleted...");
            System.out.println(outcome.getItem().toJSONPretty());

        } catch (Exception e) {
            System.err.println("Error deleting item in " + tableName);
            System.err.println(e.getMessage());
        }
    }
}