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| # Adapters | ||
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| HTTP bodies are often mappable to high-level types that your code understands. Java's HttpClient was designed | ||
| with that in mind. However, available `BodyPublisher` & `BodySubscriber` implementations are too basic, and | ||
| implementing your own can be tricky. Methanol builds upon these APIs with an extensible object mapping mechanism | ||
| that treats your objects as first-citizen HTTP bodies. | ||
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| ## Setup | ||
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| A serialization library can be integrated with Methanol through a corresponding adapter. | ||
| Adapters for the most popular serialization libraries are provided by separate modules. | ||
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| * [`methanol-gson`](adapters/gson.md): JSON with Gson | ||
| * [`methanol-jackson`](adapters/jackson.md): JSON with Jackson (but also XML, protocol buffers and other formats support by Jackson) | ||
| * [`methanol-jackson-flux`](adapters/jackson_flux.md): Streaming JSON with Jackson and Reactor | ||
| * [`methanol-jaxb`](adapters/jaxb.md): XML with JAXB | ||
| * [`methanol-jaxb-jakarta`](adapters/jaxb.md): XML with JAXB (Jakarta version) | ||
| * [`methanol-protobuf`](adapters/protobuf.md): Google's Protocol Buffers | ||
| * [`methanol-moshi`](adapters/moshi.md): JSON with Moshi, mainly for Kotlin | ||
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| We'll pick `methanol-jackson` for the examples presented here, which interact with GitHub's REST API. | ||
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| ```java | ||
| var mapper = new JsonMapper(); | ||
| var adapterCodec = | ||
| AdapterCodec.newBuilder() | ||
| .basic() | ||
| .encoder(JacksonAdapterFactory.createEncoder(mapper, MediaType.APPLICATION_JSON)) | ||
| .decoder(JacksonAdapterFactory.createDecoder(mapper, MediaType.APPLICATION_JSON)) | ||
| .build(); | ||
| var client = | ||
| Methanol.newBuilder() | ||
| .adapterCodec(adapterCodec) | ||
| .baseUri("https://api.github.com/") | ||
| .defaultHeader("Accept", "application/vnd.github.v3+json") | ||
| .build(); | ||
| ``` | ||
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| An `AdapterCodec` groups together one or more adapters, possibly targeting different mapping schemes. It helps `Methanol` | ||
| to select the correct adapter based on the request's or response's [`MediaType`](https://mizosoft.github.io/methanol/api/latest/methanol/com/github/mizosoft/methanol/MediaType.html). | ||
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| The [`basic()`][adaptercodec_basic_javadoc] calls adds the basic adapter, which encodes & decodes basic types like `String` & `InputStream`. | ||
|
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| ## Receiving Objects | ||
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| To get an `HttpResponse<T>`, give `Methanol::send` a `T.class`. | ||
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| ```java | ||
| @JsonIgnoreProperties(ignoreUnknown = true) // We'll ignore most fields for brevity. | ||
| public record GitHubUser(String login, long id, String url) {} | ||
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| GitHubUser getUser(String username) throws IOException, InterruptedException { | ||
| return client.send(MutableRequest.GET("users/" + username), GitHubUser.class).body(); | ||
| } | ||
| ``` | ||
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| If you want to get fancier with generics, pass a `TypeRef<T>`. | ||
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| ```java | ||
| @JsonIgnoreProperties(ignoreUnknown = true) // We'll ignore most fields for brevity. | ||
| public record GitHubIssue(String title, GitHubUser user, String body) {} | ||
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| List<GitHubIssue> getIssues(String owner, String repo) throws IOException, InterruptedException { | ||
| return client.send( | ||
| MutableRequest.GET("repos/" + owner + "/" + repo + "/issues"), | ||
| new TypeRef<List<GitHubIssue>>() {}).body(); | ||
| } | ||
| ``` | ||
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| ## Sending Objects | ||
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| Each `MutableRequest` can have a payload as its body. A payload is an arbitrary object that is not yet resolved into a `BodyPublisher`. | ||
| When the request is sent, the payload will be resolved with the client's `AdapterCodec`. | ||
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| ```java | ||
| public record Markdown(String text, String context, String mode) {} | ||
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| String markdownToHtml(String text, String contextRepo) throws IOException, InterruptedException { | ||
| return client.send( | ||
| MutableRequest.POST("markdown", new Markdown(text, contextRepo, "gfm"), MediaType.APPLICATION_JSON), | ||
| String.class).body(); | ||
| } | ||
| ``` | ||
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| A payload must be given along with a `MediaType` specifying the format with which it will be resolved. | ||
|
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| ## Adapters | ||
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| An adapter provides an [`Encoder`][encoder_javadoc] and/or a [`Decoder`][decoder_javadoc] implementation. | ||
| An `Encoder` creates `BodyPublisher` instances that stream a given object's serialized form. | ||
| Similarly, a `Decoder` creates `BodySubscriber<T>` instances that convert the response body into `T`. | ||
| Encoders & decoders are given [`Hints`][hints_javadoc] to customize their behavior. | ||
| One notable hint is the `MediaType`, which can be used to further describe the desired mapping format (e.g. specify a character set). | ||
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| ### Example - An HTML Adapter | ||
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| Here's an adapter that uses [Jsoup][jsoup] to convert HTML bodies to `Document` objects and vise versa. | ||
| When you're writing adapters, it's a good idea to extend from [`AbstractBodyAdapter`][abstractbodyadapter_javadoc]. | ||
|
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| ```java | ||
| public abstract class JsoupAdapter extends AbstractBodyAdapter { | ||
| JsoupAdapter() { | ||
| super(MediaType.TEXT_HTML); | ||
| } | ||
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| @Override | ||
| public boolean supportsType(TypeRef<?> type) { | ||
| return type.rawType() == Document.class; | ||
| } | ||
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| public static final class Decoder extends JsoupAdapter implements BaseDecoder { | ||
| @Override | ||
| public <T> BodySubscriber<T> toObject(TypeRef<T> typeRef, Hints hints) { | ||
| requireSupport(typeRef, hints); | ||
| var charset = hints.mediaTypeOrAny().charsetOrUtf8(); | ||
| var subscriber = BodySubscribers.mapping(BodySubscribers.ofString(charset), Jsoup::parse); | ||
| return BodySubscribers.mapping(subscriber, typeRef.exactRawType()::cast); // Safely cast Document to T. | ||
| } | ||
| } | ||
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| public static final class Encoder extends JsoupAdapter implements BaseEncoder { | ||
| @Override | ||
| public <T> BodyPublisher toBody(T value, TypeRef<T> typeRef, Hints hints) { | ||
| requireSupport(typeRef, hints); | ||
| var charset = hints.mediaTypeOrAny().charsetOrUtf8(); | ||
| var publisher = BodyPublishers.ofString(((Document) value).outerHtml(), charset); | ||
| return attachMediaType(publisher, hints.mediaTypeOrAny()); | ||
| } | ||
| } | ||
| } | ||
| ``` | ||
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| !!! tip | ||
| Make sure your encoders call `AbstractBodyAdapter::attachMediaType` so the created `BodyPublisher` can be converted to a `MimeBodyPublisher`. | ||
| That way, requests get the correct `Content-Type` header added by `Methanol`. | ||
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| ## Buffering vs Streaming | ||
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| Decoders typically load the whole response body into memory before deserialization. If your responses tend to have large bodies, | ||
| or you'd prefer the memory efficiency afforded by streaming sources, you can ask to get a `Supplier<T>` instead. | ||
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| ```java | ||
| @JsonIgnoreProperties(ignoreUnknown = true) // We'll ignore most fields for brevity. | ||
| public record GitHubUser(String login, long id, String url) {} | ||
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| GitHubUser getUser(String username) throws IOException, InterruptedException { | ||
| return client.send( | ||
| MutableRequest.GET("user/" + username), | ||
| new TypeRef<Supplier<GitHubUser>>() {}).body().get(); | ||
| } | ||
| ``` | ||
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| In such case, the response is completed as soon as all headers are read. If he decoder supports | ||
| streaming, the supplier will deserialize from a streaming source, typically an `InputStream` or a `Reader`. | ||
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| The way a `Decoder` implements streaming is by overriding `toDeferredObject` to return a `BodySubscriber<Supplier<T>>`. | ||
| Here's how it'd be properly implemented for our HTML adapter's decoder. | ||
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| ```java | ||
| @Override | ||
| public <T> BodySubscriber<Supplier<T>> toDeferredObject(TypeRef<T> typeRef, Hints hints) { | ||
| requireSupport(typeRef, hints); | ||
| return BodySubscribers.mapping( | ||
| MoreBodySubscribers.ofReader(hints.mediaTypeOrAny().charsetOrUtf8()), | ||
| reader -> | ||
| () -> | ||
| typeRef | ||
| .exactRawType() // Get Class<Document> as Class<T> | ||
| .cast( | ||
| Parser.htmlParser() | ||
| .parseInput( | ||
| new BufferedReader(reader), ""))); // Note the deferred parsing | ||
| } | ||
| ``` | ||
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| ## Legacy Adapters | ||
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| See [Legacy Adapter](legacy_adapters.md). | ||
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| [methanol_jackson]: https://github.com/mizosoft/methanol/tree/master/methanol-jackson | ||
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| [jsoup]: https://jsoup.org/ | ||
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| [encoder_javadoc]: ../api/latest/methanol/com/github/mizosoft/methanol/BodyAdapter.Encoder.html | ||
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| [decoder_javadoc]: ../api/latest/methanol/com/github/mizosoft/methanol/BodyAdapter.Decoder.html | ||
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| [bodyadapter_javadoc]: ../api/latest/methanol/com/github/mizosoft/methanol/BodyAdapter.html | ||
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| [hints_javadoc]: https://mizosoft.github.io/methanol/api/latest/methanol/com/github/mizosoft/methanol/BodyAdapter.Hints.html | ||
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| [mediatype_javadoc]: https://mizosoft.github.io/methanol/api/latest/methanol/com/github/mizosoft/methanol/MediaType.html | ||
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| [abstractbodyadapter_javadoc]: https://mizosoft.github.io/methanol/api/latest/methanol/com/github/mizosoft/methanol/adapter/AbstractBodyAdapter.html | ||
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| [adaptercodec_basic_javadoc]: https://mizosoft.github.io/methanol/api/latest/methanol/com/github/mizosoft/methanol/AdapterCodec.Builder.html#basic() |
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