azure-cosmos-java – Coding skill for AI agents

Azure Cosmos DB SDK for Java

Client library for Azure Cosmos DB NoSQL API with global distribution and reactive patterns.

Installation

<dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-cosmos</artifactId>
    <version>{reviewed_exact_version}</version>
</dependency>

Or use Azure SDK BOM:

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>com.azure</groupId>
            <artifactId>azure-sdk-bom</artifactId>
            <version>{bom_version}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

<dependencies>
    <dependency>
        <groupId>com.azure</groupId>
        <artifactId>azure-cosmos</artifactId>
    </dependency>
</dependencies>

Environment Variables

COSMOS_ENDPOINT=https://<account>.documents.azure.com:443/
COSMOS_KEY=<your-primary-key>

Authentication

Key-based Authentication

import com.azure.cosmos.CosmosClient;
import com.azure.cosmos.CosmosClientBuilder;

CosmosClient client = new CosmosClientBuilder()
    .endpoint(System.getenv("COSMOS_ENDPOINT"))
    .key(System.getenv("COSMOS_KEY"))
    .buildClient();

Async Client

import com.azure.cosmos.CosmosAsyncClient;

CosmosAsyncClient asyncClient = new CosmosClientBuilder()
    .endpoint(serviceEndpoint)
    .key(key)
    .buildAsyncClient();

With Customizations

import com.azure.cosmos.ConsistencyLevel;
import java.util.Arrays;

CosmosClient client = new CosmosClientBuilder()
    .endpoint(serviceEndpoint)
    .key(key)
    .directMode(directConnectionConfig, gatewayConnectionConfig)
    .consistencyLevel(ConsistencyLevel.SESSION)
    .connectionSharingAcrossClientsEnabled(true)
    .contentResponseOnWriteEnabled(true)
    .userAgentSuffix("my-application")
    .preferredRegions(Arrays.asList("West US", "East US"))
    .buildClient();

Client Hierarchy

| Class | Purpose |

|-------|---------|

| CosmosClient / CosmosAsyncClient | Account-level operations |

| CosmosDatabase / CosmosAsyncDatabase | Database operations |

| CosmosContainer / CosmosAsyncContainer | Container/item operations |

Core Workflow

Create Database

// Sync
var dbResponse = client.createDatabaseIfNotExists("myDatabase");
var database = client.getDatabase(dbResponse.getProperties().getId());

// Async with chaining
asyncClient.createDatabaseIfNotExists("myDatabase")
    .map(response -> asyncClient.getDatabase(response.getProperties().getId()))
    .subscribe(database -> System.out.println("Created: " + database.getId()));

Create Container

asyncClient.createDatabaseIfNotExists("myDatabase")
    .flatMap(dbResponse -> {
        String databaseId = dbResponse.getProperties().getId();
        return asyncClient.getDatabase(databaseId)
            .createContainerIfNotExists("myContainer", "/partitionKey")
            .map(containerResponse -> asyncClient.getDatabase(databaseId)
                .getContainer(containerResponse.getProperties().getId()));
    })
    .subscribe(container -> System.out.println("Container: " + container.getId()));

CRUD Operations

import com.azure.cosmos.models.PartitionKey;

CosmosAsyncContainer container = asyncClient
    .getDatabase("myDatabase")
    .getContainer("myContainer");

// Create
container.createItem(new User("1", "John Doe", "[email protected]"))
    .flatMap(response -> {
        System.out.println("Created: " + response.getItem());
        // Read
        return container.readItem(
            response.getItem().getId(),
            new PartitionKey(response.getItem().getId()),
            User.class);
    })
    .flatMap(response -> {
        System.out.println("Read: " + response.getItem());
        // Update
        User user = response.getItem();
        user.setEmail("[email protected]");
        return container.replaceItem(
            user,
            user.getId(),
            new PartitionKey(user.getId()));
    })
    .flatMap(response -> {
        // Delete
        return container.deleteItem(
            response.getItem().getId(),
            new PartitionKey(response.getItem().getId()));
    })
    .block();

Query Documents

import com.azure.cosmos.models.CosmosQueryRequestOptions;
import com.azure.cosmos.util.CosmosPagedIterable;

CosmosContainer container = client.getDatabase("myDatabase").getContainer("myContainer");

var query = new com.azure.cosmos.models.SqlQuerySpec(
    "SELECT * FROM c WHERE c.status = @status",
    java.util.List.of(new com.azure.cosmos.models.SqlParameter("@status", "active")));
CosmosQueryRequestOptions options = new CosmosQueryRequestOptions();

CosmosPagedIterable<User> results = container.queryItems(
    query,
    options,
    User.class
);

results.forEach(user -> System.out.println("User: " + user.getName()));

Key Concepts

Partition Keys

Choose a partition key with:

• High cardinality (many distinct values)
• Even distribution of data and requests
• Frequently used in queries

Consistency Levels

| Level | Guarantee |

|-------|-----------|

| Strong | Linearizability |

| Bounded Staleness | Consistent prefix with bounded lag |

| Session | Consistent prefix within session |

| Consistent Prefix | Reads never see out-of-order writes |

| Eventual | No ordering guarantee |

Request Units (RUs)

All operations consume RUs. Check response headers:

CosmosItemResponse<User> response = container.createItem(user);
System.out.println("RU charge: " + response.getRequestCharge());

Best Practices

1. Reuse CosmosClient — Create once, reuse throughout application

2. Use async client for high-throughput scenarios

3. Choose partition key carefully — Affects performance and scalability

4. Enable content response on write for immediate access to created items

5. Configure preferred regions for geo-distributed applications

6. Handle 429 errors with retry policies (built-in by default)

7. Use direct mode for lowest latency in production

Error Handling

import com.azure.cosmos.CosmosException;

try {
    container.createItem(item);
} catch (CosmosException e) {
    System.err.println("Status: " + e.getStatusCode());
    System.err.println("Message: " + e.getMessage());
    System.err.println("Request charge: " + e.getRequestCharge());
    
    if (e.getStatusCode() == 409) {
        System.err.println("Item already exists");
    } else if (e.getStatusCode() == 429) {
        System.err.println("Rate limited, retry after: " + e.getRetryAfterDuration());
    }
}

Reference Links

| Resource | URL |

|----------|-----|

| Maven Package | https://central.sonatype.com/artifact/com.azure/azure-cosmos |

| API Documentation | https://azuresdkdocs.z19.web.core.windows.net/java/azure-cosmos/latest/index.html |

| Product Docs | https://learn.microsoft.com/azure/cosmos-db/ |

| Samples | https://github.com/Azure-Samples/azure-cosmos-java-sql-api-samples |

| Performance Guide | https://learn.microsoft.com/azure/cosmos-db/performance-tips-java-sdk-v4-sql |

| Troubleshooting | https://learn.microsoft.com/azure/cosmos-db/troubleshoot-java-sdk-v4-sql |

When to Use

This skill is applicable to execute the workflow or actions described in the overview.

Limitations

• Use this skill only when the task clearly matches the scope described above.
• Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
• Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.

The CRUD example requires a User model whose serialized partition-key property matches the container path. The shown new PartitionKey(user.getId()) is valid only when that actual partition-key value equals the ID; otherwise pass the model's true partition-key value. Keep sample writes/deletes in an authorized test container, bound RU costs, and close clients on shutdown. Reactive subscriptions need completion/error handling; do not infer completion from calling subscribe().