差異處

這裏顯示兩個版本的差異處。

--- java:web:resteasy:fetch_raw_message [2018/07/01 22:55]
tony
+++ java:web:resteasy:fetch_raw_message [2023/06/25 09:48]
@@ 行 1: / 行 1: @@
-{{tag>resteasy}}
-====== RESTEasy - How to fetch raw message after the request is failed? ======
-===== Problem =====
-RESTEasy jackson provider讓我們可以輕鬆的將第三方服務回應的json內容，轉成我們自己的物件，讓程式碼只專注於資源物件的操作；然而，第三方服務並非永遠都如你預期，它可能突然更新而吐出無法處理的訊息:
-<code>
-javax.ws.rs.ProcessingException: RESTEASY003145: Unable to find a MessageBodyReader of content-type text/html;charset=iso-8859-1
-</code>
-我有幸遇到這樣的問題，也讓我思考著該如何將原始資料記錄下來以回報第三方服務提供者。本篇文章分享可能的作法，可依照你的需求自行挑選。
-===== How to resolve? =====
-==== ReadInterceptor & InputStreamSniffer ====
-一開始遇到這個問題時，我的想法是: 是否可以透過[[https://blog.wfyvv.com/blog/2018/03/jax-rs/|interceptor]]去處理? 我所提供的第一個方法，是註冊一個ReadInterceptor，並且wrap原始的InputStream，將讀取的內容給記錄下來。首先是ReaderInterceptor，它會從Context中取出InputStream，並將其wrap成InputStreamSniffer，待讀取流程執行後，就可以透過getReadContent去拿到讀取的內容:
-<code java>
-@Provider
-public class SnifferReadInterceptor implements ReaderInterceptor {
-	private InputStreamSniffer inputStreamSniffer = null;
-	@Override
-	public Object aroundReadFrom(ReaderInterceptorContext context) throws IOException, WebApplicationException {
-		InputStream inputStream = context.getInputStream();
-		inputStreamSniffer = new InputStreamSniffer(inputStream);
-		context.setInputStream(inputStreamSniffer);
-		return context.proceed();
-	}
-	public String getReadContent(){
-		return inputStreamSniffer.getContent();
-	}
-}
-</code>
-InputStreamSniffer則是將讀取的動作delegate給原始的InputStream，並悄悄地記下讀取內容:
-<code java>
-public class InputStreamSniffer extends InputStream {
-	private InputStream srcInputStream;
-	private StringBuilder contentStringBuilder;
-	public InputStreamSniffer(InputStream inputStream){
-		srcInputStream = inputStream;
-		contentStringBuilder = new StringBuilder();
-	}
-	@Override
-	public int read() throws IOException {
-		int read_c = srcInputStream.read();
-		contentStringBuilder.append((char)read_c);
-		return read_c;
-	}
-	// .. skip
-</code>
-我簡單的寫了一個測試，想要確認將message轉為json物件發生問題時，readInterceptor是否可以拿到message:
-<code java>
-@Test
-public void testSnifferReadInterceptorWithReadFailed(){
-	Invocation invocation = initInvocation();
-	Response response = null;
-	try {
-		response =  invocation.invoke();
-		response.readEntity(TestModel.class);
-		fail("should be failed	");
-	} catch( ProcessingException e ) {
-		// Can't find valid messageBodyReader
-		assertTrue(readInterceptor.getReadContent().isEmpty());
-	} finally {
-		response.close();
-	}
-}
-</code>
-答案是不行，這是由於RESTEasy在讀取訊息前，會先根據Response Header中宣告的MediaType去找尋是否有對應的MessageBodyRead。
-==== Read All Content of ReadInterceptor ====
-由於我們無法於執行過程中解決這個問題，因此改在ReadInterceptor中，先將所有內容讀出來:
-<code java>
-public class DebugReadInterceptor  implements ReaderInterceptor{
-	private String content;
-	@Override
-	public Object aroundReadFrom(ReaderInterceptorContext context) throws IOException, WebApplicationException {
-		InputStream inputStream = context.getInputStream();
-		content = IOUtils.toString(inputStream);
-		context.setInputStream(new ByteArrayInputStream(content.getBytes()));
-		return context.proceed();
-	}
-	public String getContent(){
-		return content;
-	}
-}
-</code>
-這個方法是可以解決目前遇到的問題，但缺點是每次請求都一定會多處理一次內容。於是我把腦筋動到了MessageBodyReader身上。
-==== Customized MessageBodyReader ====
-我新增一個名為CompositeMessageBodyProvider的類別，去extend MessageBodyReader；isReadable永遠回傳true，將搜尋合適MessageBodyReader動作交由readFrom處理，如果找不到就丟ProcessingException上去。Client可以攔截此例外決定要處理的方式:
-<code java>
-@Provider
-@Consumes(MediaType.WILDCARD)
-@Produces(MediaType.WILDCARD)
-public class CompositeMessageBodyProvider implements MessageBodyReader<Object>, MessageBodyWriter<Object> {
-	private List<MessageBodyReader<Object>> messageBodyReaders = new ArrayList<>();
-	@Override
-	public boolean isReadable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
-		return true;
-	}
-	private Optional<MessageBodyReader<Object>> findReader(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType){
-		return messageBodyReaders.stream().filter(writter->writter.isReadable(type, genericType, annotations, mediaType)).findAny();
-	}
-	@Override
-	public Object readFrom(Class<Object> type, Type genericType, Annotation[] annotations, MediaType mediaType,
-			MultivaluedMap<String, String> httpHeaders, InputStream entityStream)
-			throws IOException, WebApplicationException {
-		Optional<MessageBodyReader<Object>> reader = findReader(type, genericType, annotations, mediaType);
-		if(reader.isPresent()){
-			return reader.get().readFrom(type, genericType, annotations, mediaType, httpHeaders, entityStream);
-		}
-		String output = IOUtils.toString(entityStream);
-		throw new ProcessingException("Unexpected content: " + output);
-	}
-	// .. skip
-</code>
-===== Summary =====
-以parse error、unexpected media type與unexpected json content(parse ok)三種錯誤來說:
-  - ReadInterceptor & InputStreamSniffer: 適用於parse error與unexpected json content。
-  - Read All Content of ReadInterceptor: 適用於以上提及的所有錯誤情形，但效率較差。
-  - Customized MessageBodyReader: 適用於unexpected media type。
-要使用哪種方式，可仔細評估後再決定。
-===== Reference =====
-  - [[https://blog.wfyvv.com/blog/2018/03/jax-rs/|JAX-RS 2.0 简介及其过滤器与拦截器]]
-  - [[https://dennis-xlc.gitbooks.io/restful-java-with-jax-rs-2-0-en/cn/part1/chapter12/ordering_filters_and_interceptors.html|Ordering Filters and Interceptors]]
-=====    =====
-----
-\\
-~~DISQUS~~