在Azure Blob的官方示例中，都是对文件进行上传到Blob操作，没有实现对已创建的Blob进行追加的操作。如果想要实现对一个文件的多次追加操作，每一次写入的时候，只传入新的内容？

(相关资料图)

Azure Storage Blob 有三种类型： Block Blob, Append Blob 和 Page Blob。其中，只有Append Blob类型支持追加(Append)操作。并且Blob类型在创建时就已经确定，无法后期修改。

在查看Java Storage SDK后，发现可以使用AppendBlobClient来实现。

/**     * Creates a new {@link AppendBlobClient} associated with this blob.     *     * @return A {@link AppendBlobClient} associated with this blob.     */    public AppendBlobClient getAppendBlobClient() {        return new SpecializedBlobClientBuilder()            .blobClient(this)            .buildAppendBlobClient();    }

在 AppendBlobClient 类，有appendBlock 和 appendBlockWithResponse 等多种方法来实现追加。方法定义源码如下：

/**     * Commits a new block of data to the end of the existing append blob.     * 
     * Note that the data passed must be replayable if retries are enabled (the default). In other words, the     * {@code Flux} must produce the same data each time it is subscribed to.     *     * 
Code Samples
     *     * {@codesnippet com.azure.storage.blob.specialized.AppendBlobClient.appendBlock#InputStream-long}     *     * @param data The data to write to the blob. The data must be markable. This is in order to support retries. If     * the data is not markable, consider using {@link #getBlobOutputStream()} and writing to the returned OutputStream.     * Alternatively, consider wrapping your data source in a {@link java.io.BufferedInputStream} to add mark support.     * @param length The exact length of the data. It is important that this value match precisely the length of the     * data emitted by the {@code Flux}.     * @return The information of the append blob operation.     */    @ServiceMethod(returns = ReturnType.SINGLE)    public AppendBlobItem appendBlock(InputStream data, long length) {        return appendBlockWithResponse(data, length, null, null, null, Context.NONE).getValue();    }    /**     * Commits a new block of data to the end of the existing append blob.     * 
     * Note that the data passed must be replayable if retries are enabled (the default). In other words, the     * {@code Flux} must produce the same data each time it is subscribed to.     *     * 
Code Samples
     *     * {@codesnippet com.azure.storage.blob.specialized.AppendBlobClient.appendBlockWithResponse#InputStream-long-byte-AppendBlobRequestConditions-Duration-Context}     *     * @param data The data to write to the blob. The data must be markable. This is in order to support retries. If     * the data is not markable, consider using {@link #getBlobOutputStream()} and writing to the returned OutputStream.     * Alternatively, consider wrapping your data source in a {@link java.io.BufferedInputStream} to add mark support.     * @param length The exact length of the data. It is important that this value match precisely the length of the     * data emitted by the {@code Flux}.     * @param contentMd5 An MD5 hash of the block content. This hash is used to verify the integrity of the block during     * transport. When this header is specified, the storage service compares the hash of the content that has arrived     * with this header value. Note that this MD5 hash is not stored with the blob. If the two hashes do not match, the     * operation will fail.     * @param appendBlobRequestConditions {@link AppendBlobRequestConditions}     * @param timeout An optional timeout value beyond which a {@link RuntimeException} will be raised.     * @param context Additional context that is passed through the Http pipeline during the service call.     * @return A {@link Response} whose {@link Response#getValue() value} contains the append blob operation.     * @throws UnexpectedLengthException when the length of data does not match the input {@code length}.     * @throws NullPointerException if the input data is null.     */    @ServiceMethod(returns = ReturnType.SINGLE)    public Response appendBlockWithResponse(InputStream data, long length, byte[] contentMd5,        AppendBlobRequestConditions appendBlobRequestConditions, Duration timeout, Context context) {        Objects.requireNonNull(data, ""data" cannot be null.");        Flux fbb = Utility.convertStreamToByteBuffer(data, length, MAX_APPEND_BLOCK_BYTES, true);        Mono> response = appendBlobAsyncClient.appendBlockWithResponse(            fbb.subscribeOn(Schedulers.elastic()), length, contentMd5, appendBlobRequestConditions, context);        return StorageImplUtils.blockWithOptionalTimeout(response, timeout);    }

第一步: 在Java项目 pom.xml 中引入Azure Storage Blob依赖

      com.azure      azure-storage-blob      12.13.0    

第二步: 引入必要的 Storage 类

import java.io.ByteArrayInputStream; import java.io.IOException;import java.io.InputStream;import java.net.URISyntaxException;import java.nio.charset.StandardCharsets;import java.security.InvalidKeyException;import java.security.MessageDigest;import java.security.NoSuchAlgorithmException; import java.time.LocalTime; import com.azure.core.http.rest.Response; import com.azure.storage.blob.BlobContainerClient;import com.azure.storage.blob.BlobServiceClient;import com.azure.storage.blob.BlobServiceClientBuilder;import com.azure.storage.blob.models.AppendBlobItem;import com.azure.storage.blob.models.AppendBlobRequestConditions; import com.azure.storage.blob.specialized.AppendBlobClient; 

第三步：创建AppendBlobClient 对象，使用 BlobServiceClient 及连接字符串(Connection String)

String storageConnectionString = "DefaultEndpointsProtocol=https;AccountName=*****;AccountKey=*******;EndpointSuffix=core.chinacloudapi.cn";                String containerName = "appendblob";                String fileName = "test.txt";                // Create a BlobServiceClient object which will be used to create a container                System.out.println("\nCreate a BlobServiceClient Object to Connect Storage Account");                BlobServiceClient blobServiceClient = new BlobServiceClientBuilder()                                .connectionString(storageConnectionString)                                .buildClient();                BlobContainerClient containerClient = blobServiceClient.getBlobContainerClient(containerName);                if (!containerClient.exists())                        containerClient.create();                // Get a reference to a blob                AppendBlobClient appendBlobClient = containerClient.getBlobClient(fileName).getAppendBlobClient();

第四步：调用appendBlockWithResponse 方法追加内容，并根据返回状态码判断是否追加成功

boolean overwrite = true; // Default value                if (!appendBlobClient.exists())                        System.out.printf("Created AppendBlob at %s%n",                                        appendBlobClient.create(overwrite).getLastModified());                String data = "Test to append new content into exists blob! by blogs lu bian liang zhan deng @"                                + LocalTime.now().toString() + "\n";                InputStream inputStream = new ByteArrayInputStream(data.getBytes(StandardCharsets.UTF_8));                byte[] md5 = MessageDigest.getInstance("MD5").digest(data.getBytes(StandardCharsets.UTF_8));                AppendBlobRequestConditions requestConditions = new AppendBlobRequestConditions();                // Context context = new Context("key", "value");                long length = data.getBytes().length;                Response rsp = appendBlobClient.appendBlockWithResponse(inputStream, length, md5,                                requestConditions, null, null);                if (rsp.getStatusCode() == 201) {                        System.out.println("append content successful........");                }

但如果操作的Blob类型不是Append Blob，就会遇见错误Status code 409 ---- The blob type is invalid for this operation 错误

Exception in thread "main" com.azure.storage.blob.models.BlobStorageException: Status code 409, ">InvalidBlobTypeThe blob type is invalid for this operation.RequestId:501ee0b9-301e-0003-4f7b-829ca6000000Time:2023-05-09T13:37:17.7509942Z"        at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:67)        at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500)        at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:484)        at com.azure.core.http.rest.RestProxy.instantiateUnexpectedException(RestProxy.java:343)        at com.azure.core.http.rest.RestProxy.lambda$ensureExpectedStatus$5(RestProxy.java:382)        at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:125)        at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1815)        at reactor.core.publisher.MonoCacheTime$CoordinatorSubscriber.signalCached(MonoCacheTime.java:337)        at reactor.core.publisher.MonoCacheTime$CoordinatorSubscriber.onNext(MonoCacheTime.java:354)        at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2397)        at reactor.core.publisher.MonoCacheTime$CoordinatorSubscriber.onSubscribe(MonoCacheTime.java:293)        at reactor.core.publisher.FluxFlatMap.trySubscribeScalarMap(FluxFlatMap.java:192)        at reactor.core.publisher.MonoFlatMap.subscribeOrReturn(MonoFlatMap.java:53)        at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:57)        at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)        at reactor.core.publisher.MonoCacheTime.subscribeOrReturn(MonoCacheTime.java:143)        at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:57)        at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:157)        at reactor.core.publisher.FluxDoFinally$DoFinallySubscriber.onNext(FluxDoFinally.java:130)        at reactor.core.publisher.FluxHandle$HandleSubscriber.onNext(FluxHandle.java:118)        at reactor.core.publisher.FluxMap$MapConditionalSubscriber.onNext(FluxMap.java:220)        at reactor.core.publisher.FluxDoFinally$DoFinallySubscriber.onNext(FluxDoFinally.java:130)        at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.onNext(FluxHandleFuseable.java:184)        at reactor.core.publisher.FluxContextWrite$ContextWriteSubscriber.onNext(FluxContextWrite.java:107)        at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1815)        at reactor.core.publisher.MonoCollectList$MonoCollectListSubscriber.onComplete(MonoCollectList.java:128)        at reactor.core.publisher.FluxPeek$PeekSubscriber.onComplete(FluxPeek.java:259)        at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:142)        at reactor.netty.channel.FluxReceive.onInboundComplete(FluxReceive.java:401)        at reactor.netty.channel.ChannelOperations.onInboundComplete(ChannelOperations.java:416)        at reactor.netty.channel.ChannelOperations.terminate(ChannelOperations.java:470)        at reactor.netty.http.client.HttpClientOperations.onInboundNext(HttpClientOperations.java:685)        at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:94)        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379)        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365)        at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:655)        at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:581)        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493)        at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989)        at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)        at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)        at java.base/java.lang.Thread.run(Thread.java:1589)        Suppressed: java.lang.Exception: #block terminated with an error                at reactor.core.publisher.BlockingSingleSubscriber.blockingGet(BlockingSingleSubscriber.java:99)                at reactor.core.publisher.Mono.block(Mono.java:1703)                at com.azure.storage.common.implementation.StorageImplUtils.blockWithOptionalTimeout(StorageImplUtils.java:128)                at com.azure.storage.blob.specialized.AppendBlobClient.appendBlockWithResponse(AppendBlobClient.java:259)                at test.App.AppendBlobContent(App.java:68)                at test.App.main(App.java:31)

appendBlockWithResponse ：https://learn.microsoft.com/en-us/java/api/com.azure.storage.blob.specialized.appendblobclient?view=azure-java-stable#com-azure-storage-blob-specialized-appendblobclient-appendblockwithresponse(java-io-inputstream-long-byte()-com-azure-storage-blob-models-appendblobrequestconditions-java-time-duration-com-azure-core-util-context)

Blob（对象）存储简介 :https://docs.azure.cn/zh-cn/storage/blobs/storage-blobs-introduction