# TryDaxHelper.java
<a name="DAX.client.run-application-java.TryDaxHelper"></a>

`TryDaxHelper.java` 文件包含一些实用程序方法。

`getDynamoDBClient` 和 `getDaxClient` 方法提供 Amazon DynamoDB 和 DynamoDB Accelerator (DAX) 客户端。为了实现控制层面操作（`CreateTable`、`DeleteTable`）和写入操作，程序使用 DynamoDB 客户端。如果指定 DAX 集群端点，则主程序将创建一个 DAX 客户端，用于执行读取操作（`GetItem`、`Query`、`Scan`）。

其他 `TryDaxHelper` 方法（`createTable`、`writeData`、`deleteTable`）用于设置和停用 DynamoDB 表及其数据。

可以通过多种方式修改程序：
+ 对表使用不同的预置吞吐量设置。
+ 修改写入的每个项目的大小（参见 `writeData` 方法的 `stringSize` 变量)。
+ 修改 `GetItem`、`Query` 和 `Scan` 测试的数量及其参数。
+ 注释掉包含 `helper.CreateTable` 和 `helper.DeleteTable` 的行（如果不希望每次运行程序时都创建和删除表）。

**注意**  
 要运行此程序，您可以设置 Maven 将 DAX SDK for Java 客户端和 适用于 Java 的 AWS SDK 作为依赖项。有关更多信息，请参阅 [使用客户端作为 Apache Maven 依赖项](DAX.client.java-sdk-v1.md#DAXClient.Maven)。  
或者可以下载 DAX Java 客户端和 适用于 Java 的 AWS SDK 并加入类路径。有关设置 [Java 和 DAX](DAX.client.run-application-java.md) 变量的示例，请参阅 `CLASSPATH`。

```
import com.amazon.dax.client.dynamodbv2.AmazonDaxClientBuilder;
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.model.AttributeDefinition;
import com.amazonaws.services.dynamodbv2.model.KeySchemaElement;
import com.amazonaws.services.dynamodbv2.model.KeyType;
import com.amazonaws.services.dynamodbv2.model.ProvisionedThroughput;
import com.amazonaws.services.dynamodbv2.model.ScalarAttributeType;
import com.amazonaws.util.EC2MetadataUtils;

public class TryDaxHelper {

    private static final String region = EC2MetadataUtils.getEC2InstanceRegion();

    DynamoDB getDynamoDBClient() {
        System.out.println("Creating a DynamoDB client");
        AmazonDynamoDB client = AmazonDynamoDBClientBuilder.standard()
                .withRegion(region)
                .build();
        return new DynamoDB(client);
    }

    DynamoDB getDaxClient(String daxEndpoint) {
        System.out.println("Creating a DAX client with cluster endpoint " + daxEndpoint);
        AmazonDaxClientBuilder daxClientBuilder = AmazonDaxClientBuilder.standard();
        daxClientBuilder.withRegion(region).withEndpointConfiguration(daxEndpoint);
        AmazonDynamoDB client = daxClientBuilder.build();
        return new DynamoDB(client);
    }

    void createTable(String tableName, DynamoDB client) {
        Table table = client.getTable(tableName);
        try {
            System.out.println("Attempting to create table; please wait...");

            table = client.createTable(tableName,
                    Arrays.asList(
                            new KeySchemaElement("pk", KeyType.HASH), // Partition key
                            new KeySchemaElement("sk", KeyType.RANGE)), // Sort key
                    Arrays.asList(
                            new AttributeDefinition("pk", ScalarAttributeType.N),
                            new AttributeDefinition("sk", ScalarAttributeType.N)),
                    new ProvisionedThroughput(10L, 10L));
            table.waitForActive();
            System.out.println("Successfully created table.  Table status: " +
                    table.getDescription().getTableStatus());

        } catch (Exception e) {
            System.err.println("Unable to create table: ");
            e.printStackTrace();
        }
    }

    void writeData(String tableName, DynamoDB client, int pkmax, int skmax) {
        Table table = client.getTable(tableName);
        System.out.println("Writing data to the table...");

        int stringSize = 1000;
        StringBuilder sb = new StringBuilder(stringSize);
        for (int i = 0; i < stringSize; i++) {
            sb.append('X');
        }
        String someData = sb.toString();

        try {
            for (Integer ipk = 1; ipk <= pkmax; ipk++) {
                System.out.println(("Writing " + skmax + " items for partition key: " + ipk));
                for (Integer isk = 1; isk <= skmax; isk++) {
                    table.putItem(new Item()
                            .withPrimaryKey("pk", ipk, "sk", isk)
                            .withString("someData", someData));
                }
            }
        } catch (Exception e) {
            System.err.println("Unable to write item:");
            e.printStackTrace();
        }
    }

    void deleteTable(String tableName, DynamoDB client) {
        Table table = client.getTable(tableName);
        try {
            System.out.println("\nAttempting to delete table; please wait...");
            table.delete();
            table.waitForDelete();
            System.out.println("Successfully deleted table.");

        } catch (Exception e) {
            System.err.println("Unable to delete table: ");
            e.printStackTrace();
        }
    }

}
```