CAT 中实现异步请求的调用链查看
我们可以先父线程消息树的上下文信息保存下来，然后在子线程使用。先写一个存放上下文信息的地方：
public class ContextWarehouse {
private static ThreadLocal<CatContext> contextThreadLocal = new ThreadLocal();
public static void setContext(final CatContext context) {
contextThreadLocal.set(context);
}
public static CatContext getContext() {
//先从 ContextWarehouse 中获取上下文信息
CatContext context = contextThreadLocal.get();
if (context == null) {
context = new CatContext();
Cat.logRemoteCallClient(context);
}
return context;
}
}
实现 Callable 接口，创建一个自定义的类，实现了在子线程中存放父线程的上下文信息的功能：
public class OneMoreCallable<V> implements Callable<V> {
private CatContext catContext;
private Callable<V> callable;
public DdCallable(final Callable<V> callable) {
this.callable = callable;
this.catContext = new CatContext();
//获取父线程消息树的上下文信息
Cat.logRemoteCallClient(this.catContext)
;
}
@Override
public V call() throws Exception {
//保存父线程消息树的上下文信息到子线程
ContextWarehouse.setContext(this.catContext);
return callable.call();
}
}
定义一些常量，在调用 API 时作为 header 中的 key：
public class CatHttpConstants {
public static final String CAT_HTTP_HEADER_CHILD_MESSAGE_ID = "DD-CAT-CHILD-MESSAGE-ID";
public static final String CAT_HTTP_HEADER_PARENT_MESSAGE_ID = "DD-CAT-PARENT-MESSAGE-ID";
public static final String CAT_HTTP_HEADER_ROOT_MESSAGE_ID = "DD-CAT-ROOT-MESSAGE-ID";
}
埋点时，在调用 API 的 HttpClient 工具类中统一增加代码，以 GET 方式为例：
public class HttpClientUtil {
public static String doGet(String url) throws IOException {
HttpGet httpGet = new HttpGet(url);
CloseableHttpResponse response = null;
CloseableHttpClient httpClient = HttpClientBuilder.create().build();
String content = null;
Transaction t = Cat.newTransaction(CatConstants.TYPE_CALL, url);
try {
CatContext context = ContextWarehouse.getContext();
httpGet.setHeader(CatHttpConstants.CAT_HTTP_HEADER_ROOT_MESSAGE_ID, context.getProperty(Cat.Context.ROOT));
httpGet.setHeader(CatHttpConstants.CAT_HTTP_HEADER_PARENT_MESSAGE_ID, context.getProperty(Cat.Context.PARENT));
httpGet.setHeader(CatHttpConstants.CAT_HTTP_HEADER_CHILD_MESSAGE_ID, context.getProperty(Cat.Context.CHILD));
response = httpClient.execute(httpGet);
if (response.getStatusLine().getStatusCode() == 200) {
content = EntityUtils.toString(response.getEntity(), "UTF-8");
t.setStatus(Transaction.SUCCESS);
}
} catch (Exception e) {
Cat.logError(e);
t.setStatus(e);
throw e;
} finally {
if (response != null) {
response.close();
}
if (httpClient != null) {
httpClient.close();
}
t.complete();
}
return content;
}
}
异步请求实例
下面写一个异步请求的实例，通过多个商品 ID 异步获取对应的商品详细信息：
public class ProductService {
/**
声明一个大小固定为 10 的线程池
*/
private static ExecutorService executor = Executors.newFixedThreadPool(10);
/**
通过商品 ID 列表异步获取对应的商品详细信息
@param productIds 商品 ID 列表
@return 对应的商品详细信息
*/
public List<String> findProductInfo(List<Long> productIds) {
List<Future<String>> futures = new ArrayList<>();
for (Long productId : productIds) {
futures.add(executor.submit(new DdCallable(() -> {
try {
//调用获取商品详细信息的 API
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