本文為英文版的機器翻譯版本，如內容有任何歧義或不一致之處，概以英文版為準。

# 修改適用於 Java 1.x 的開發套件的現有應用程式來使用 DAX
<a name="DAX.client.modify-your-app.java-sdk-v1"></a>

如果您已有使用 Amazon DynamoDB 的 Java 應用程式，則需要進行修改，使其可存取您的 DynamoDB Accelerator (DAX) 叢集。您不需要重新撰寫整個應用程式，因為 DAX Java 用戶端與 適用於 Java 的 AWS SDK中所含的 DynamoDB 低階用戶端十分相似。

**注意**  
這些指示適用於使用適用於 Java 的 AWS SDK 1.x 的應用程式。如需使用適用於 Java 2.x 的 AWS 軟體開發套件的應用程式，請參閱 [修改現有應用程式以使用 DAX](DAX.client.modify-your-app.md)。

假設您有名為 `Music` 的 DynamoDB 資料表。資料表的分割區索引鍵為 `Artist`，而排序索引鍵為 `SongTitle`。以下程式會直接讀取 `Music` 資料表中的項目。

```
import java.util.HashMap;

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClientBuilder;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;
import com.amazonaws.services.dynamodbv2.model.GetItemRequest;
import com.amazonaws.services.dynamodbv2.model.GetItemResult;

public class GetMusicItem {

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

        // Create a DynamoDB client
        AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard().build();

        HashMap<String, AttributeValue> key = new HashMap<String, AttributeValue>();
        key.put("Artist", new AttributeValue().withS("No One You Know"));
        key.put("SongTitle", new AttributeValue().withS("Scared of My Shadow"));

        GetItemRequest request = new GetItemRequest()
            .withTableName("Music").withKey(key);

        try {
            System.out.println("Attempting to read the item...");
            GetItemResult result = client.getItem(request);
            System.out.println("GetItem succeeded: " + result);

        } catch (Exception e) {
            System.err.println("Unable to read item");
            System.err.println(e.getMessage());
        }
    }
}
```

若要修改程式，請將 DynamoDB 用戶端取代為 DAX 用戶端。

```
import java.util.HashMap;

import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazon.dax.client.dynamodbv2.AmazonDaxClientBuilder;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;
import com.amazonaws.services.dynamodbv2.model.GetItemRequest;
import com.amazonaws.services.dynamodbv2.model.GetItemResult;

public class GetMusicItem {

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

    //Create a DAX client

    AmazonDaxClientBuilder daxClientBuilder = AmazonDaxClientBuilder.standard();
    daxClientBuilder.withRegion("us-east-1").withEndpointConfiguration("mydaxcluster.2cmrwl.clustercfg.dax.use1.cache.amazonaws.com:8111");
    AmazonDynamoDB client = daxClientBuilder.build();


       /*
       ** ...
       ** Remaining code omitted (it is identical)
       ** ...
       */

    }
}
```

## 使用 DynamoDB 文件 API
<a name="DAX.client.modify-your-app.document-api"></a>

 適用於 Java 的 AWS SDK 提供 DynamoDB 的文件界面。文件 API 會作為低階 DynamoDB 用戶端的包裝函式。如需詳細資訊，請參閱[文件介面](https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Programming.SDKs.Interfaces.Document.html)。

文件介面也可以與低階 DAX 用戶端搭配使用，如以下範例所示。

```
import com.amazonaws.services.dynamodbv2.AmazonDynamoDB;
import com.amazon.dax.client.dynamodbv2.AmazonDaxClientBuilder;
import com.amazonaws.services.dynamodbv2.document.DynamoDB;
import com.amazonaws.services.dynamodbv2.document.GetItemOutcome;
import com.amazonaws.services.dynamodbv2.document.Table;

public class GetMusicItemWithDocumentApi {

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

        //Create a DAX client

        AmazonDaxClientBuilder daxClientBuilder = AmazonDaxClientBuilder.standard();
        daxClientBuilder.withRegion("us-east-1").withEndpointConfiguration("mydaxcluster.2cmrwl.clustercfg.dax.use1.cache.amazonaws.com:8111");
        AmazonDynamoDB client = daxClientBuilder.build();

        // Document client wrapper
        DynamoDB docClient = new DynamoDB(client);

        Table table = docClient.getTable("Music");

        try {
            System.out.println("Attempting to read the item...");
            GetItemOutcome outcome = table.tgetItemOutcome(
                "Artist", "No One You Know",
                "SongTitle", "Scared of My Shadow");
            System.out.println(outcome.getItem());
            System.out.println("GetItem succeeded: " + outcome);
        } catch (Exception e) {
            System.err.println("Unable to read item");
            System.err.println(e.getMessage());
        }

    }
}
```

## DAX 非同步用戶端
<a name="DAX.client.async"></a>

`AmazonDaxClient` 是同步的。針對長時間執行的 DAX API 操作 (例如大型資料表 `Scan`)，這可能會封鎖程式執行，直到操作完成。如果程式需要在 DAX API 操作進行時執行其他工作，您可以改用 `ClusterDaxAsyncClient`。

下列程式示範如何使用 `ClusterDaxAsyncClient` 和 Java `Future` 來實作非封鎖解決方案。

```
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;

import com.amazon.dax.client.dynamodbv2.ClientConfig;
import com.amazon.dax.client.dynamodbv2.ClusterDaxAsyncClient;
import com.amazonaws.auth.profile.ProfileCredentialsProvider;
import com.amazonaws.handlers.AsyncHandler;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBAsync;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;
import com.amazonaws.services.dynamodbv2.model.GetItemRequest;
import com.amazonaws.services.dynamodbv2.model.GetItemResult;

public class DaxAsyncClientDemo {
	public static void main(String[] args) throws Exception {

		ClientConfig daxConfig = new ClientConfig().withCredentialsProvider(new ProfileCredentialsProvider())
				.withEndpoints("mydaxcluster.2cmrwl.clustercfg.dax.use1.cache.amazonaws.com:8111");

		AmazonDynamoDBAsync client = new ClusterDaxAsyncClient(daxConfig);

		HashMap<String, AttributeValue> key = new HashMap<String, AttributeValue>();
		key.put("Artist", new AttributeValue().withS("No One You Know"));
		key.put("SongTitle", new AttributeValue().withS("Scared of My Shadow"));

		GetItemRequest request = new GetItemRequest()
				.withTableName("Music").withKey(key);

		// Java Futures
		Future<GetItemResult> call = client.getItemAsync(request);
		while (!call.isDone()) {
			// Do other processing while you're waiting for the response
			System.out.println("Doing something else for a few seconds...");
			Thread.sleep(3000);
		}
		// The results should be ready by now

		try {
			call.get();

		} catch (ExecutionException ee) {
			// Futures always wrap errors as an ExecutionException.
			// The *real* exception is stored as the cause of the
			// ExecutionException
			Throwable exception = ee.getCause();
			System.out.println("Error getting item: " + exception.getMessage());
		}

		// Async callbacks
		call = client.getItemAsync(request, new AsyncHandler<GetItemRequest, GetItemResult>() {

			@Override
			public void onSuccess(GetItemRequest request, GetItemResult getItemResult) {
				System.out.println("Result: " + getItemResult);
			}

			@Override
			public void onError(Exception e) {
				System.out.println("Unable to read item");
				System.err.println(e.getMessage());
				// Callers can also test if exception is an instance of
				// AmazonServiceException or AmazonClientException and cast
				// it to get additional information
			}

		});
		call.get();

	}
}
```