Contoh: Menangani atribut tipe biner menggunakan AWS SDK for Java dokumen API

Contoh kode Java berikut menggambarkan penanganan atribut jenis biner. Contoh tersebut menambahkan item ke tabel Reply. Item termasuk atribut jenis biner (ExtendedMessage) yang menyimpan data terkompresi. Contoh tersebut kemudian mengambil item dan mencetak semua nilai atribut. Sebagai ilustrasi, contoh menggunakan kelas GZIPOutputStream untuk mengompresi aliran sampel dan menetapkannya ke atribut ExtendedMessage. Ketika atribut binari diambil, atribut didekompresi menggunakan kelas GZIPInputStream.

catatan

The SDK for Java juga menyediakan model persistensi objek, memungkinkan Anda untuk memetakan kelas sisi klien Anda ke tabel DynamoDB. Pendekatan ini dapat mengurangi jumlah kode yang harus Anda tulis. Untuk informasi selengkapnya, lihat Java 1.x: D ynamoDBMapper.

Jika Anda mengikuti bagian Membuat tabel dan memuat data untuk contoh kode di DynamoDB, semestinya Anda telah membuat tabel Reply. Anda juga dapat membuat tabel ini secara terprogram. Untuk informasi selengkapnya, lihat Membuat tabel contoh dan mengunggah data menggunakan AWS SDK for Java.

Untuk step-by-step petunjuk pengujian sampel berikut, lihatContoh kode Java.

contoh

package com.amazonaws.codesamples.document;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.TimeZone;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
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.spec.GetItemSpec;

public class DocumentAPIItemBinaryExample {

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

    static String tableName = "Reply";
    static SimpleDateFormat dateFormatter = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");

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

            // Format the primary key values
            String threadId = "Amazon DynamoDB#DynamoDB Thread 2";

            dateFormatter.setTimeZone(TimeZone.getTimeZone("UTC"));
            String replyDateTime = dateFormatter.format(new Date());

            // Add a new reply with a binary attribute type
            createItem(threadId, replyDateTime);

            // Retrieve the reply with a binary attribute type
            retrieveItem(threadId, replyDateTime);

            // clean up by deleting the item
            deleteItem(threadId, replyDateTime);
        } catch (Exception e) {
            System.err.println("Error running the binary attribute type example: " + e);
            e.printStackTrace(System.err);
        }
    }

    public static void createItem(String threadId, String replyDateTime) throws IOException {

        Table table = dynamoDB.getTable(tableName);

        // Craft a long message
        String messageInput = "Long message to be compressed in a lengthy forum reply";

        // Compress the long message
        ByteBuffer compressedMessage = compressString(messageInput.toString());

        table.putItem(new Item().withPrimaryKey("Id", threadId).withString("ReplyDateTime", replyDateTime)
                .withString("Message", "Long message follows").withBinary("ExtendedMessage", compressedMessage)
                .withString("PostedBy", "User A"));
    }

    public static void retrieveItem(String threadId, String replyDateTime) throws IOException {

        Table table = dynamoDB.getTable(tableName);

        GetItemSpec spec = new GetItemSpec().withPrimaryKey("Id", threadId, "ReplyDateTime", replyDateTime)
                .withConsistentRead(true);

        Item item = table.getItem(spec);

        // Uncompress the reply message and print
        String uncompressed = uncompressString(ByteBuffer.wrap(item.getBinary("ExtendedMessage")));

        System.out.println("Reply message:\n" + " Id: " + item.getString("Id") + "\n" + " ReplyDateTime: "
                + item.getString("ReplyDateTime") + "\n" + " PostedBy: " + item.getString("PostedBy") + "\n"
                + " Message: "
                + item.getString("Message") + "\n" + " ExtendedMessage (uncompressed): " + uncompressed + "\n");
    }

    public static void deleteItem(String threadId, String replyDateTime) {

        Table table = dynamoDB.getTable(tableName);
        table.deleteItem("Id", threadId, "ReplyDateTime", replyDateTime);
    }

    private static ByteBuffer compressString(String input) throws IOException {
        // Compress the UTF-8 encoded String into a byte[]
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        GZIPOutputStream os = new GZIPOutputStream(baos);
        os.write(input.getBytes("UTF-8"));
        os.close();
        baos.close();
        byte[] compressedBytes = baos.toByteArray();

        // The following code writes the compressed bytes to a ByteBuffer.
        // A simpler way to do this is by simply calling
        // ByteBuffer.wrap(compressedBytes);
        // However, the longer form below shows the importance of resetting the
        // position of the buffer
        // back to the beginning of the buffer if you are writing bytes directly
        // to it, since the SDK
        // will consider only the bytes after the current position when sending
        // data to DynamoDB.
        // Using the "wrap" method automatically resets the position to zero.
        ByteBuffer buffer = ByteBuffer.allocate(compressedBytes.length);
        buffer.put(compressedBytes, 0, compressedBytes.length);
        buffer.position(0); // Important: reset the position of the ByteBuffer
                            // to the beginning
        return buffer;
    }

    private static String uncompressString(ByteBuffer input) throws IOException {
        byte[] bytes = input.array();
        ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        GZIPInputStream is = new GZIPInputStream(bais);

        int chunkSize = 1024;
        byte[] buffer = new byte[chunkSize];
        int length = 0;
        while ((length = is.read(buffer, 0, chunkSize)) != -1) {
            baos.write(buffer, 0, length);
        }

        String result = new String(baos.toByteArray(), "UTF-8");

        is.close();
        baos.close();
        bais.close();

        return result;
    }
}