# 示例：使用 适用于 Java 的 AWS SDK 文档 API 的 CRUD 操作
<a name="JavaDocumentAPICRUDExample"></a>

以下代码示例介绍对 Amazon DynamoDB 项目的 CRUD 操作。该示例创建一个项目、对其进行检索、执行多种更新，最终删除项目。

**注意**  
SDK for Java 还提供一个对象持久化模型，可用来将客户端类映射到 DynamoDB 表。该方法可以减少需要编写的代码数量。有关更多信息，请参阅 [Java 1.x：DynamoDBMapper](DynamoDBMapper.md)。

**注意**  
此代码示例假定您已按照 [为 DynamoDB 中的代码示例创建表和加载数据](SampleData.md) 部分的说明，将数据加载到您的帐户的 DynamoDB 中。  
有关运行以下示例的分步说明，请参阅 [Java 代码示例](CodeSamples.Java.md)。

```
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());
        }
    }
}
```