流数据是向Web浏览器发送数据的一种全新方法，可显着加快页面加载速度。通常，我们需要允许用户在Web应用程序中下载文件。当数据太大时，提供良好的用户体验变得非常困难，使用StreamingResponseBody，我们现在可以轻松地为高度并发的应用程序流式传输数据。
在本文中，我们将看一个使用StreamingResponseBody下载文件的示例。在这种方法中，数据被处理并以块的形式写入OutputStream。
设置Spring Boot项目
为Maven POM添加一些基本依赖项：
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.techshard.streamingresponse</groupId>
<artifactId>springboot-download</artifactId>
<version>1.0-SNAPSHOT</version>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.4.RELEASE</version>
<relativePath />
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
</dependency>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-io</artifactId>
<version>1.3.2</version>
</dependency>
</dependencies>
</project>
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我们现在将创建一个控制器并添加一个API端点以供下载。这是完整的控制器。@RestController
@RequestMapping ("/api")
public class DownloadController {
private final Logger logger = LoggerFactory.getLogger(DownloadController.class);
@GetMapping (value = "/download", produces = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<StreamingResponseBody> download(final HttpServletResponse response) {
response.setContentType("application/zip");
response.setHeader(
"Content-Disposition",
"attachment;filename=sample.zip");
StreamingResponseBody stream = out -> {
final String home = System.getProperty("user.home");
final File directory = new File(home + File.separator + "Documents" + File.separator + "sample");
final ZipOutputStream zipOut = new ZipOutputStream(response.getOutputStream());
if(directory.exists() && directory.isDirectory()) {
try {
for (final File file : directory.listFiles()) {
final InputStream inputStream=new FileInputStream(file);
final ZipEntry zipEntry=new ZipEntry(file.getName());
zipOut.putNextEntry(zipEntry);
byte[] bytes=new byte[1024];
int length;
while ((length=inputStream.read(bytes)) >= 0) {
zipOut.write(bytes, 0, length);
}
inputStream.close();
}
zipOut.close();
} catch (final IOException e) {
logger.error("Exception while reading and streaming data {} ", e);
}
}
};
logger.info("steaming response {} ", stream);
return new ResponseEntity(stream, HttpStatus.OK);
}
}
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在此API端点中，我们从目录中读取多个文件并创建zip文件。我们在StreamingResponseBody中执行此过程。在使用 ResponseEntity将写入的信息传递回客户端之前， 会将数据直接写入OutputStream 。这意味着下载过程将立即在客户端上启动，而服务器正在处理并以块的形式写入数据。
动服务器并使用http：// localhost：8080 / api / download测试此端点 。
使用StreamingResponseBody时，强烈建议配置Spring MVC中使用的TaskExecutor来执行异步请求。TaskExecutor是一个抽象Runnable执行的接口。
让我们配置TaskExecutor。这是AsyncConfiguration类，它使用WebMvcCofigurer配置超时，并且还注册在超时时调用的拦截器，以防您需要一些特殊处理。
@Configuration
@EnableAsync
@EnableScheduling
public class AsyncConfiguration implements AsyncConfigurer {
private final Logger log = LoggerFactory.getLogger(AsyncConfiguration.class);
@Override
@Bean (name = "taskExecutor")
public AsyncTaskExecutor getAsyncExecutor() {
log.debug("Creating Async Task Executor");
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
executor.setCorePoolSize(5);
executor.setMaxPoolSize(10);
executor.setQueueCapacity(25);
return executor;
}
@Override
public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
return new SimpleAsyncUncaughtExceptionHandler();
}
/** Configure async support for Spring MVC. */
@Bean
public WebMvcConfigurer webMvcConfigurerConfigurer(AsyncTaskExecutor taskExecutor, CallableProcessingInterceptor callableProcessingInterceptor) {
return new WebMvcConfigurer() {
@Override
public void configureAsyncSupport(AsyncSupportConfigurer configurer) {
configurer.setDefaultTimeout(360000).setTaskExecutor(taskExecutor);
configurer.registerCallableInterceptors(callableProcessingInterceptor);
WebMvcConfigurer.super.configureAsyncSupport(configurer);
}
};
}
@Bean
public CallableProcessingInterceptor callableProcessingInterceptor() {
return new TimeoutCallableProcessingInterceptor() {
@Override
public <T> Object handleTimeout(NativeWebRequest request, Callable<T> task) throws Exception {
log.error("timeout!");
return super.handleTimeout(request, task);
}
};
}
}
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在GitHub存储库中找到本文的示例。