亚马逊DynamoDB

2022-04-08 14:59:09

介绍

Amazon DynamoDB是一项完全托管的NoSQL数据库服务，可提供无缝的可扩展性和快速可预测的性能。
Amazon DynamoDB自动将表的数据和流量分布在足够数量的服务器上，以处理客户指定的请求容量和存储的数据量，同时保持一致且快速的性能。
所有数据项都存储在固态磁盘（SSD）上，并自动跨区域中的多个可用区复制，以提供内置的高可用性和数据持久性。
您可以通过AWS管理控制台启动新的Amazon DynamoDB数据库表，在不停机或性能下降的情况下扩展或缩减对该表的请求容量，并获得对资源利用率和性能指标的可见性。
借助Amazon DynamoDB，您可以将操作和扩展分布式数据库的管理负担转移到AWS，因此您不必担心硬件设置，设置和配置，复制，软件修补或集群扩展。
SDK： http ： //aws.amazon.com/sdkforjava/

Amazon DynamoDB注释

@DynamoDBTable

标识Amazon DynamoDB中的目标表。例如，以下Java代码段定义了一个类Developer，并将其映射到Amazon DynamoDB中的People表。


@DynamoDBTable(tableName="People")
public class Developer { ...}

@DynamoDBIgnore

向DynamoDBMapper实例指示应该忽略关联的属性。将数据保存到表时，DynamoDBMapper不会将此属性保存到表中。

@DynamoDBAttribute

将属性映射到表属性。默认情况下，每个类属性都映射到具有相同名称的item属性。但是，如果名称不同，则可以使用此标记将属性映射到属性。在以下Java代码段中，DynamoDBAttribute将BookAuthors属性映射到表中的Authors属性名称。


@DynamoDBAttribute(attributeName = "Authors")
public List<String> getBookAuthors() { return BookAuthors; }
public void setBookAuthors(List<String> BookAuthors) { this.BookAuthors = BookAuthors; }

将对象保存到表时，DynamoDBMapper使用作者作为属性名称。

@DynamoDBHashKey

将类属性映射到表的hash属性。该属性必须是受支持的String或Numeric类型之一，并且不能是集合类型。

假设您有一个表ProductCatalog，该表具有ID作为主键。以下Java代码段定义了CatalogItem类，并使用@DynamoDBHashKey标记将其id属性映射到ProductCatalog表的主键。


@DynamoDBTable(tableName="ProductCatalog")
public class CatalogItem {
   private String Id;   
  @DynamoDBHashKey(attributeName="Id")
  public String getId() {
       return Id;
  }
  public void setId(String Id) {
       this.Id = Id;
  }
  // Additional properties go here.
}

@DynamoDBRangeKey

将类属性映射到表的范围键属性。如果主键是由哈希键和范围键属性组成的，则可以使用此标记将您的类字段映射到范围属性。例如，假定您有一个“回复”表，其中存储有论坛主题的回复。每个线程可以有很多回复。因此，该表的主键是ThreadId和ReplyDateTime。 ThreadId是哈希属性，ReplyDateTime是范围属性。以下Java代码段定义了Reply类，并将其映射到Reply表。它同时使用@DynamoDBHashKey和@DynamoDBRangeKeytags来标识映射到主键的类属性。


@DynamoDBTable(tableName="Reply")
public class Reply {
   private String id;
   private String replyDateTime;
 
   @DynamoDBHashKey(attributeName="Id")
   public String getId() { return id; }
   public void setId(String id) { this.id = id; }
 
   @DynamoDBRangeKey(attributeName="ReplyDateTime")
   public String getReplyDateTime() { return replyDateTime; }
   public void setReplyDateTime(String replyDateTime) { this.replyDateTime = replyDateTime; }
 
  // Additional properties go here.
}

@DynamoDBAutoGeneratedKey

将哈希键或范围键属性标记为自动生成。保存这些属性时，对象持久性模型将生成一个随机UUID。只能将字符串属性标记为自动生成的键。

以下代码段演示了如何使用自动生成的密钥。


@DynamoDBTable(tableName="AutoGeneratedKeysExample")
public class AutoGeneratedKeys {
   private String id;
   private String payload;
   
   @DynamoDBHashKey(attributeName = "Id")
   @DynamoDBAutoGeneratedKey
   public String getId() { return id; }
   public void setId(String id) { this.id = id; }
 
   @DynamoDBAttribute(attributeName="payload")
   public String getPayload() { return this.payload };
   public String setPayload(String payload) { this.payload = payload };   
  
   public static void saveItem() {
       AutoGeneratedKeys obj = new AutoGeneratedKeys();
       obj.setPayload("abc123");
       
       // id field is null at this point       
       DynamoDBMapper mapper = new DynamoDBMapper(dynamoDBClient);
       mapper.save(obj);
       
       System.out.println("Object was saved with id " + obj.getId());
   }
}

@DynamoDBVersionAttribute

标识用于存储乐观锁定版本号的类属性。 DynamoDBMapper保存新项目时，会为此属性分配一个版本号，并在每次更新该项目时将其递增。仅支持数字标量类型。

DynamoDBMapper类别

DynamoDBMapper类是Amazon DynamoDB的入口点。它提供了与Amazon DynamoDB的连接，并使您能够访问各种表中的数据，对项目执行各种CRUD操作以及对表执行查询和扫描。此类提供以下关键操作，供您使用Amazon DynamoDB。

救
- 将指定的对象保存到表中。

mapper.save(obj, new DynamoDBMapperConfig(DynamoDBMapperConfig.SaveBehavior.CLOBBER));

加载
- 从表中检索项目。


CatalogItem item = mapper.load(CatalogItem.class, item.getId(),
               new DynamoDBMapperConfig(DynamoDBMapperConfig.ConsistentReads.CONSISTENT));

删除
- 从表中删除一个项目。

询问
- 启用表查询。


String forumName = "Amazon DynamoDB";
String forumSubject = "DynamoDB Thread 1";
String hashKey = forumName + "#" + forumSubject;
 
long twoWeeksAgoMilli = (new Date()).getTime() - (14L*24L*60L*60L*1000L);
Date twoWeeksAgo = new Date();
twoWeeksAgo.setTime(twoWeeksAgoMilli);
SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");
String twoWeeksAgoStr = df.format(twoWeeksAgo);
 
Condition rangeKeyCondition = new Condition()
.withComparisonOperator(ComparisonOperator.GT.toString())
.withAttributeValueList(new AttributeValue().withS(twoWeeksAgoStr.toString()));
 
Reply replyKey = new Reply();
replyKey.setId(hashKey);
 
DynamoDBQueryExpression<Reply> queryExpression = new DynamoDBQueryExpression<Reply>()
.withHashKeyValues(replyKey)
.withRangeKeyCondition("ReplyDateTime", rangeKeyCondition);
 
List<Reply> latestReplies = mapper.query(Reply.class, queryExpression);

该查询返回Reply对象的集合。

扫描
- 扫描整个表。


DynamoDBScanExpression scanExpression = new DynamoDBScanExpression();
 
Map<String, Condition> scanFilter = new HashMap<String, Condition>();
Condition scanCondition = new Condition()
.withComparisonOperator(ComparisonOperator.EQ.toString())
.withAttributeValueList(new AttributeValue().withN("0"));
 
scanFilter.put("Answered", scanCondition);
 
scanExpression.setScanFilter(scanFilter);
 
List<Thread> unansweredThreads = mapper.scan(Thread.class, scanExpression);

扫描方法返回“延迟加载”集合。它初仅返回一页结果，然后在需要时对下一页进行服务调用。要获取所有匹配项，您仅需要遍历unansweredThreads集合。

batchDelete
- 使用对AmazonDynamoDB.batchWriteItem方法的一个或多个调用从一个或多个表中删除对象。


Book book1 = mapper.load(Book.class, 901);
Book book2 = mapper.load(Book.class, 902);
mapper.batchDelete(Arrays.asList(book1, book2));

batchSave
- 使用对AmazonDynamoDB.batchWriteItem方法的一个或多个调用将对象保存到一个或多个表。


Book book1 = new Book();
book1.id = 901;
book1.productCategory = "Book";
book1.title = "Book 901 Title";
 
Book book2 = new Book();
book2.id = 902;
book2.productCategory = "Book";
book2.title = "Book 902 Title";
 
mapper.batchSave(Arrays.asList(book1, book2));

batchWrite
- 使用对AmazonDynamoDB.batchWriteItem方法的一个或多个调用，将对象保存到一个或多个表并从一个或多个表中删除对象。


// Create a Forum item to save
Forum forumItem = new Forum();
forumItem.name = "Test BatchWrite Forum";
 
// Create a Thread item to save
Thread threadItem = new Thread();
threadItem.forumName = "AmazonDynamoDB";
threadItem.subject = "My sample question";
 
// Load a ProductCatalog item to delete
Book book3 = mapper.load(Book.class, 903);
 
List<Object> objectsToWrite = Arrays.asList(forumItem, threadItem);
List<Book> objectsToDelete = Arrays.asList(book3);
 
mapper.batchWrite(objectsToWrite, objectsToDelete);

计数
- 计算指定的扫描表达式并返回匹配项的计数。

marshallIntoObject
- 一种将结果从低级API转换为域对象的实用程序方法。

支持的数据类型

Amazon DynamoDB支持以下原始数据类型和原始包装器类。

串
布尔，布尔
字节，字节
日期（作为ISO8601毫秒精度的字符串，转换为UTC）
日历（作为ISO8601毫秒精度的字符串，已转换为UTC）
好久好久
整数，整数
双倍
浮，浮
大十进制
大整数

Amazon DynamoDB支持Java Set集合类型。如果映射的集合属性不是Set，则将引发异常。

下表总结了前面的Java类型如何映射到Amazon DynamoDB类型。

Java类型	Amazon DynamoDB类型
所有数字类型	N（数字类型）
弦乐	S（字符串类型）
布尔值	N（数字类型），0或1。
字节缓冲区	B（二进制类型）
日期	S（字符串类型）。日期值存储为ISO-8601格式的字符串。
设置收集类型	SS（字符串集）类型，NS（数字集）类型或BS（二进制集）类型。

Java示例：CRUD操作

CatalogItem.java


import java.util.Set;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBAttribute;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBHashKey;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBTable;
@DynamoDBTable(tableName="ProductCatalog")
public class CatalogItem {
    private Integer id;
    private String title;
    private String ISBN;
    private Set bookAuthors;
 
    @DynamoDBHashKey(attributeName="Id")
    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = id; }
 
    @DynamoDBAttribute(attributeName="Title")
    public String getTitle() { return title; }    
    public void setTitle(String title) { this.title = title; }
 
    @DynamoDBAttribute(attributeName="ISBN")
    public String getISBN() { return ISBN; }    
    public void setISBN(String ISBN) { this.ISBN = ISBN;}
 
    @DynamoDBAttribute(attributeName = "Authors")
    public Set getBookAuthors() { return bookAuthors; }    
    public void setBookAuthors(Set bookAuthors) { this.bookAuthors = bookAuthors; }
 
    @Override
    public String toString() {
       return "Book [ISBN=" + ISBN + ", bookAuthors=" + bookAuthors
       + ", id=" + id + ", title=" + title + "]";            
    }
}

ObjectPersistenceCRUDExample.java


import java.io.IOException;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Random;
 
import com.amazonaws.AmazonClientException;
import com.amazonaws.AmazonServiceException;
import com.amazonaws.auth.AWSCredentials;
import com.amazonaws.auth.ClasspathPropertiesFileCredentialsProvider;
import com.amazonaws.regions.Region;
import com.amazonaws.regions.Regions;
import com.amazonaws.services.dynamodbv2.AmazonDynamoDBClient;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper;
import com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapperConfig;
import com.amazonaws.services.dynamodbv2.model.AttributeDefinition;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;
import com.amazonaws.services.dynamodbv2.model.ComparisonOperator;
import com.amazonaws.services.dynamodbv2.model.Condition;
import com.amazonaws.services.dynamodbv2.model.CreateTableRequest;
import com.amazonaws.services.dynamodbv2.model.DescribeTableRequest;
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.services.dynamodbv2.model.ScanRequest;
import com.amazonaws.services.dynamodbv2.model.ScanResult;
import com.amazonaws.services.dynamodbv2.model.TableDescription;
import com.amazonaws.services.dynamodbv2.model.TableStatus;
 
public class ObjectPersistenceCRUDExample {
 static AmazonDynamoDBClient client;
 private DynamoDBMapper mapper;
 private static int PRODUCT_ID;
 
 public static void main(String[] args) throws IOException {
  ObjectPersistenceCRUDExample demo = new ObjectPersistenceCRUDExample();
  demo.init();
  demo.createTable("ProductCatalog");
  for (int i = ; i < 100; i++) {
   System.out.println(i);
   PRODUCT_ID = PRODUCT_ID + i;
   demo.insert();
  }
  demo.getAllRows();
  CatalogItem itemRetrieved = demo.load(PRODUCT_ID);
  demo.update(itemRetrieved);
  CatalogItem updatedItem = demo.load(PRODUCT_ID);
  demo.delete(updatedItem);
  demo.load(updatedItem.getId());
  System.out.println("Example complete!");
 }
 
 private void init() {
  PRODUCT_ID = new Random().nextInt(1000);
  AWSCredentials credentials = new ClasspathPropertiesFileCredentialsProvider()
    .getCredentials();
  client = new AmazonDynamoDBClient(credentials);
  Region usWest2 = Region.getRegion(Regions.US_WEST_2);
  client.setRegion(usWest2);
  mapper = new DynamoDBMapper(client);
 }
 
 private void createTable(String tableName) {
  try {
   CreateTableRequest createTableRequest = new CreateTableRequest()
     .withTableName(tableName);
   createTableRequest.withKeySchema(new KeySchemaElement()
     .withAttributeName("Id").withKeyType(KeyType.HASH));
   createTableRequest
     .withAttributeDefinitions(new AttributeDefinition()
       .withAttributeName("Id").withAttributeType(
         ScalarAttributeType.N));
   createTableRequest
     .withProvisionedThroughput(new ProvisionedThroughput()
       .withReadCapacityUnits(10L).withWriteCapacityUnits(
         10L));
   TableDescription createdTableDescription = client.createTable(
     createTableRequest).getTableDescription();
   System.out.println("Created Table: " + createdTableDescription);
   // Wait for it to become active
   waitForTableToBecomeAvailable(tableName);
  } catch (AmazonServiceException e) {
   e.printStackTrace();
  } catch (AmazonClientException e) {
   e.printStackTrace();
  }
 }
 
 private void waitForTableToBecomeAvailable(String tableName) {
  System.out.println("Waiting for " + tableName + " to become ACTIVE...");
  long startTime = System.currentTimeMillis();
  long endTime = startTime + (10 * 60 * 1000);
  while (System.currentTimeMillis() < endTime) {
   try {
    Thread.sleep(1000 * 20);
   } catch (Exception e) {
   }
   try {
    DescribeTableRequest request = new DescribeTableRequest()
      .withTableName(tableName);
    TableDescription tableDescription = client.describeTable(
      request).getTable();
    String tableStatus = tableDescription.getTableStatus();
    System.out.println("  - current state: " + tableStatus);
    if (tableStatus.equals(TableStatus.ACTIVE.toString()))
     return;
   } catch (AmazonServiceException ase) {
    if (ase.getErrorCode().equalsIgnoreCase(
      "ResourceNotFoundException") == false)
     throw ase;
   }
  }
  throw new RuntimeException("Table " + tableName + " never went active");
 }
 
 private void insert() {
  CatalogItem item = new CatalogItem();
  item.setId(PRODUCT_ID);
  item.setTitle("Book PRODUCT_ID");
  item.setISBN("611-1111111111");
  item.setBookAuthors(new HashSet(Arrays.asList("Author1",
    "Author2")));
  // Save the item (book).
  mapper.save(item);
 }
 
 private void update(CatalogItem itemRetrieved) {
  itemRetrieved.setISBN("622-2222222222");
  itemRetrieved.setBookAuthors(new HashSet(Arrays.asList(
    "Author1", "Author3")));
  mapper.save(itemRetrieved);
  System.out.println("Item updated:");
  System.out.println(itemRetrieved);
 }
 
 private void delete(CatalogItem updatedItem) {
  // Delete the item.
  mapper.delete(updatedItem);
 }
 
 private CatalogItem load(int id) {
  // Retrieve the updated item.
  DynamoDBMapperConfig config = new DynamoDBMapperConfig(
    DynamoDBMapperConfig.ConsistentReads.CONSISTENT);
  CatalogItem updatedItem = mapper.load(CatalogItem.class, id, config);
  if (updatedItem == null) {
   System.out.println("Done - Sample item is deleted.");
  } else {
   System.out.println("Retrieved item:");
   System.out.println(updatedItem);
  }
  return updatedItem;
 }
 
 private void getAllRows() {
  ScanRequest scanRequest = new ScanRequest()
    .withTableName("ProductCatalog");
  scanRequest.setLimit(10);
  HashMap scanFilter = new HashMap();
  Condition condition = new Condition().withComparisonOperator(
    ComparisonOperator.EQ.toString()).withAttributeValueList(
    new AttributeValue().withS("611-1111111111"));
  scanFilter.put("ISBN", condition);
  Condition condition2 = new Condition().withComparisonOperator(
    ComparisonOperator.LE.toString()).withAttributeValueList(
    new AttributeValue().withN("1000"));
  scanFilter.put("Id", condition2);
  scanRequest.withScanFilter(scanFilter);
  try {
   System.out.println("Scan Request: " + scanRequest);
   ScanResult scanResponse = client.scan(scanRequest);
   for (Map item : scanResponse.getItems()) {
    System.out.println(item.get("Id").getN() + " , " +
    item.get("ISBN").getS() + " , " +
    item.get("Authors").getSS() + " , " +
    item.get("Title").getS());
   }
   System.out.println("Scan Response: " + scanResponse);
   System.out.println("Count: " + scanResponse.getCount());
   System.out.println("Scanned Count: "
     + scanResponse.getScannedCount());
   System.out.println("Items: " + scanResponse.getItems());
  } catch (AmazonServiceException e) {
   e.printStackTrace();
  } catch (AmazonClientException e) {
   e.printStackTrace();
  }
 }
    }

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Amazon DynamoDB

创建时间：2022-04-08 14:56:47

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