JavaBodyParsers

内容处理

什么是内容处理?

一个HTTP请求(至少是使用了POST和PUT操作的)的内容可以被格式化成任何指定的格式，指定格式在Content-Type header。一个内容解析器负责将请求的内容转成对应的java值

注意: 你不能直接用java来重写'内容解析器'的实现，因为一个play'内容解析器'必须使用'Iteratee[Array[Byte], A]'来处理内容，'Iteratee[Array[Byte], A]'必须用scala来实现。

但是play提供绝大多数的默认的'内容解析器'(parsing Json, Xml, Text, uploading files),你可以重用默认的解析器来创建你自己的java实现的解析器；比如你可以在Text解析器的基础上自定义一个PDF解析器

内容解析器 的Java API

In the Java API, all body parsers must generate a play.mvc.Http.RequestBody value. This value computed by the body parser can then be retrieved via request().body():

public static Result index() {
  RequestBody body = request().body();
  return ok("Got body: " + body);
}

You can specify the BodyParser to use for a particular action using the @BodyParser.Of annotation:

@BodyParser.Of(BodyParser.Json.class)
public static Result index() {
  RequestBody body = request().body();
  return ok("Got json: " + body.asJson());
}

The Http.RequestBody API

As we just said all body parsers in the Java API will give you a play.mvc.Http.RequestBody value. From this body object you can retrieve the request body content in the most appropriate Java type.

Note: The RequestBody methods like asText() or asJson() will return null if the parser used to compute this request body doesn't support this content type. For example in an action method annotated with @BodyParser.Of(BodyParser.Json.class), calling asXml() on the generated body will retun null.

Some parsers can provide a most specific type than Http.RequestBody (ie. a subclass of Http.RequestBody). You can automatically cast the request body into another type using the as(...) helper method:

@BodyParser.Of(BodyLengthParser.class)
pulic static Result index() {
  BodyLength body = request().body().as(BodyLength.class);
  ok("Request body length: " + body.getLength());
}

默认内容处理: 任意内容

If you don't specify your own body parser, Play will use the default one guessing the most appropriate content type from the Content-Type header:

• text/plain: String, accessible via asText()
• application/json: JsonNode, accessible via asJson()
• text/xml: org.w3c.Document, accessible via asXml()
• application/form-url-encoded: Map<String, String[]>, accessible via asFormUrlEncoded()
• multipart/form-data: Http.MultipartFormData, accessible via asMultipartFormData()
• Any other content type: Http.RawBuffer, accessible via asRaw()

Example:

pulic static Result save() {
  RequestBody body = request().body();
  String textBody = body.asText();
  
  if(textBody != null) {
    ok("Got: " + text);
  } else {
    badRequest("Expecting text/plain request body");
  }
}

最大内容长度

Text based body parsers (such as text, json, xml or formUrlEncoded) use a max content length because they have to load all the content into memory.

There is a default content length (the default is 100KB).

Tip: The default content size can be defined in application.conf:

parsers.text.maxLength=128K

You can also specify a maximum content length via the @BodyParser.Of annotation:

// Accept only 10KB of data.
@BodyParser.Of(value = BodyParser.Text.class, maxLength = 10 * 1024)
pulic static Result index() {
  if(request().body().isMaxSizeExceeded()) {
    return badRequest("Too much data!");
  } else {
    ok("Got body: " + request().body().asText()); 
  }
}

Next: Actions composition