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1. Four ways of passing parameters of HTTP Protocol examples of the composition of HTTP protocols correspond to Spring annotations path info pass parameters / articles/12 (query articles with id of 12, 12 are parameters) @ PathVariableURL Query String / articles?id=12@RequestParamBody pass parameters Content-Type: multipart/form-data@RequestParamBody pass parameters Content-Type: application/json Or other custom format @ RequestBodyHeaders parameter @ RequestHeader II, commonly used notes Review 2.1 @ RequestBody and @ ResponseBody// Note that @ RequestBody is not required to be used in pairs with @ ResponseBody. Public @ ResponseBody AjaxResponse saveArticle (@ RequestBody ArticleVO article)

As shown in the code above:

@ RequestBody modifies the request parameter and annotations are used to receive the body of HTTP. The default is to use the format of JSON.

@ ResponseBody modifies the return value, and the annotation is used to carry response data in the body of HTTP. The default format is JSON. Without this annotation, the spring response string type is the development mode that jumps to a template page or jsp page. To put it bluntly: with this annotation, you are developing a data interface, and without this annotation, you are developing a page jump controller.

After using the @ ResponseBody annotation, the program does not go to the view parser or render the html view, but returns the object directly to the request sender in the form of data (the default JSON). So we have a question: what if we want to receive or XML data? What should we do if we want to respond to the data format of excel? We will answer this question later.

2.2. @ RequestMapping comment

The @ RequestMapping annotation is the most interesting of all commonly used annotations to mark HTTP service endpoints. Many of its properties play an important role in enriching our application development methods. Such as:

Value: application request endpoint, the core attribute, used to mark the uniqueness of the request processing method

Method: the method type of HTTP protocol, such as GET, POST, PUT, DELETE, etc.

Consumes: the data type (Content-Type) of the HTTP protocol request content, such as application/json, text/html

Produces: the data type of the HTTP protocol response content. It will be explained in more detail below.

Params: the annotated method is allowed to process the request only if some parameter values must be included in the HTTP request.

Headers: the HTTP request must contain some specified header value to allow the annotated method to process the request.

@ RequestMapping (value = "/ article", method = POST) @ PostMapping (value = "/ article")

The two writing methods in the above code have the same effect, that is, the method of PostMapping equals @ RequestMapping equals POST. In the same way: @ GetMapping, @ PutMapping, @ DeleteMapping are all written in a simple way.

2.3. @ RestController and @ Controller

The @ Controller annotation is the most commonly used annotation in development, and its purpose has two meanings:

One is to tell Spring that the class annotated by this annotation is a Bean of Spring and needs to be injected into the context of Spring.

Second, all annotations annotated by RequestMapping in this class are HTTP service endpoints.

@ RestController is equivalent to @ Controller and @ ResponseBody. It has two meanings:

First, as the role of Controller, the controller class is injected into the Spring context, and the RequestMapping annotation method of this class is HTTP service endpoint.

Second, as the role of ResponseBody, the default serialization method for request response is JSON, rather than jumping to jsp or template pages.

2.4. @ PathVariable and @ RequestParam

PathVariable is used for {parameter} on URI, and the following method is used to delete an article, where id is the article id. For example, if our request URL is "/ article/1", then it will match DeleteMapping and PathVariable will receive the parameter id=1. RequestParam is used to receive parameter data submitted by normal form or ajax simulation form.

@ DeleteMapping ("/ article/ {id}") public @ ResponseBody AjaxResponse deleteArticle (@ PathVariable Long id) {@ PostMapping ("/ article") public @ ResponseBody AjaxResponse deleteArticle (@ RequestParam Long id) {II. Receive complex nested object parameters

Some friends may not understand the true meaning of the existence of RequestBody annotations, form data submission using RequestParam, why come up with a RequestBody annotation? The real meaning of RequestBody annotations is the ability to receive front-end data using objects or nested objects.

If you take a closer look at the code above, you can see that a paramData object contains a bestFriend object. This data structure cannot be received using RequestParam, and RequestParam can only accept flat, one-to-one parameters. For the parameters of the data structure like the one above, we need to define two classes on the java server, one is ParamData and the other is BestFriend.

Public class ParamData {private String name; private int id; private String phone; private BestFriend bestFriend; public static class BestFriend {private String address; private String sex;}}

Notice that the necessary java plain model elements, such as GET and SET methods, are omitted from the above code.

Note that the member variable name must correspond to the JSON attribute name.

Pay attention to receiving different types of parameters and using different types of member variables

After completing the above action, we can use @ RequestBody ParamData paramData to receive all the above complex nested object parameters at once, and all the properties of the parameter object will be assigned.

III. The principle of Http data conversion

The use of JSON is now more common, it is easy to use, strong expression ability, and is the first choice for most data interface applications. So how do you respond to other types of data? What is the principle of discrimination? The following is an introduction to you:

When an HTTP request arrives, it is an InputStream, which is converted to a java object through HttpMessageConverter, and parameters are received.

When responding to a HTTP request, we first output a java object, which is then converted by HttpMessageConverter to OutputStream output.

When we integrate jackson's class library into the Spring Boot application, some of the following HttpMessageConverter will be loaded.

Class function description: StringHttpMessageConverter converts request information into a string FormHttpMessageConverter reads form data into MultiValueMap XmlAwareFormHttpMessageConverter extension and FormHttpMessageConverter, if some of the form attributes are XML data, the converter can be used to read ResourceHttpMessageConverter read and write org.springframework.core.io.Resource objects BufferedImageHttpMessageConverter read write BufferedImage objects ByteArrayHttpMessageConverter read write binary data SourceHttpMessageConverter read write java.xml.transform.Source type objects MarshallingHttpMessageConverter read and write XML messages Jaxb2RootElementHttpMessageConverter read and write XML messages through JAXB2 through Spring org.springframework,xml.Marshaller and Unmarshaller MappingJacksonHttpMessageConverter in a class that converts request messages into annotated XmlRootElement and XmlType connections uses ObjectMapper of the Jackson open source package to read and write JSON data RssChannelHttpMessageConverter read and write RSS seed messages AtomFeedHttpMessageConverter and RssChannelHttpMessageConverter can read and write RSS seed messages

Which HttpMessageConverter is used is determined by the Accept and Content-Type properties of the HTTP protocol, as well as the parameter data type. When using RequestBody or ResponseBody, combined with the Accept data type sent by the front end, it will automatically determine the priority of using MappingJacksonHttpMessageConverter as the data converter. However, not only JSON can express object data types, but so can XML. How do we tell Spring if we want to use the XML format, we need to use the produces attribute.

@ GetMapping (value = "/ demo", produces = MediaType.APPLICATION_XML_VALUE)

Here we explicitly tell you that the returned data type is xml, and we will use Jaxb2RootElementHttpMessageConverter as the default data converter. Of course, the implementation of XML data response is a little more complex than JSON, and it needs to be used in conjunction with annotated entity classes such as @ XmlRootElement, @ XmlElement, and so on. In the same way, you can also use the consumes attribute.

IV. Custom HttpMessageConverter

In fact, most of the data formats do not require us to customize HttpMessageConverter, and there are third-party class libraries that can help us implement them (including the Excel format in the following code). But sometimes, the output format of some data does not have a class library like Jackson to help us deal with it, so we need to customize the data format. What should I do?

Let's write a custom HTTP type converter using the Excel data format as an example. The effect of the implementation is that when we return the data type AjaxResponse, we automatically convert the AjaxResponse to the Excel data response to the client.

Org.apache.poi poi-ooxml 3.9@Servicepublic class ResponseToXlsConverter extends AbstractHttpMessageConverter {private static final MediaType EXCEL_TYPE = MediaType.valueOf ("application/vnd.ms-excel"); ResponseToXlsConverter () {super (EXCEL_TYPE);} @ Override protected AjaxResponse readInternal (final Class clazz) {return (AjaxResponse.class = = clazz) } @ Override protected void writeInternal (final AjaxResponse ajaxResponse, final HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException {final Workbook workbook = new HSSFWorkbook (); final Sheet sheet = workbook.createSheet (); final Row row = sheet.createRow (0); row.createCell (0) .setCellValue (ajaxResponse.getMessage ()); row.createCell (1) .setCellValue (ajaxResponse.getData (). ToString ()); workbook.write (outputMessage.getBody ()) }}

Implement the AbstractHttpMessageConverter interface

Specify which data format the converter is for? Such as "application/vnd.ms-excel" in the code above

Specify which object data types are targeted by the converter? Such as the supports function in the code above

Use writeInternal to output the data, which in the above example is in Excel format.

Thank you for your reading, the above is the content of "Spring common notes and http data conversion methods". After the study of this article, I believe you have a deeper understanding of Spring common annotations and http data conversion methods, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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