Spring Boot Multipart File Upload With Json

77. Jump MVC

Jump Kick has a number of starters that include Spring MVC. Note that some starters include a dependency on Jump MVC rather than include it direct. This department answers common questions about Leap MVC and Leap Kick.

77.1 Write a JSON REST Service

Any Bound @RestController in a Bound Boot awarding should return JSON response by default equally long every bit Jackson2 is on the classpath, as shown in the post-obit example:

            @RestController            public            form            MyController {            @RequestMapping("/thing")            public            MyThing thing() {            return            new            MyThing(); 	}  }

Equally long equally MyThing can be serialized by Jackson2 (true for a normal POJO or Groovy object), then localhost:8080/thing serves a JSON representation of it by default. Note that, in a browser, you might sometimes come across XML responses, considering browsers tend to send take headers that prefer XML.

77.two Write an XML Balance Service

If y'all have the Jackson XML extension (jackson-dataformat-xml) on the classpath, you lot can apply it to render XML responses. The previous instance that we used for JSON would work. To utilize the Jackson XML renderer, add the post-obit dependency to your projection:

            <dependency>            <groupId>com.fasterxml.jackson.dataformat</groupId>            <artifactId>jackson-dataformat-xml</artifactId>            </dependency>          

If Jackson's XML extension is non available, JAXB (provided by default in the JDK) is used, with the additional requirement of having MyThing annotated equally @XmlRootElement, every bit shown in the following example:

            @XmlRootElement            public            class            MyThing {            private            String name; 	 }

To become the server to render XML instead of JSON, you might take to transport an Accept: text/xml header (or use a browser).

77.3 Customize the Jackson ObjectMapper

Jump MVC (customer and server side) uses HttpMessageConverters to negotiate content conversion in an HTTP substitution. If Jackson is on the classpath, y'all already become the default converter(s) provided by Jackson2ObjectMapperBuilder, an case of which is auto-configured for you.

The ObjectMapper (or XmlMapper for Jackson XML converter) example (created past default) has the following customized backdrop:

• MapperFeature.DEFAULT_VIEW_INCLUSION is disabled
• DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES is disabled
• SerializationFeature.WRITE_DATES_AS_TIMESTAMPS is disabled

Jump Kicking also has some features to make it easier to customize this beliefs.

Y'all tin configure the ObjectMapper and XmlMapper instances by using the environment. Jackson provides an extensive suite of unproblematic on/off features that can be used to configure various aspects of its processing. These features are described in six enums (in Jackson) that map onto backdrop in the environment:

Enum	Property	Values
com.fasterxml.jackson.databind.DeserializationFeature	leap.jackson.deserialization.<feature_name>	true, imitation
com.fasterxml.jackson.core.JsonGenerator.Feature	jump.jackson.generator.<feature_name>	true, faux
com.fasterxml.jackson.databind.MapperFeature	spring.jackson.mapper.<feature_name>	true, false
com.fasterxml.jackson.core.JsonParser.Feature	bound.jackson.parser.<feature_name>	true, fake
com.fasterxml.jackson.databind.SerializationFeature	jump.jackson.serialization.<feature_name>	true, simulated
com.fasterxml.jackson.annotation.JsonInclude.Include	jump.jackson.default-holding-inclusion	always, non_null, non_absent, non_default, non_empty

For example, to enable pretty print, ready spring.jackson.serialization.indent_output=truthful. Annotation that, cheers to the utilize of relaxed binding, the example of indent_output does not accept to match the case of the corresponding enum constant, which is INDENT_OUTPUT.

This environment-based configuration is applied to the car-configured Jackson2ObjectMapperBuilder edible bean and applies to any mappers created by using the architect, including the auto-configured ObjectMapper bean.

The context's Jackson2ObjectMapperBuilder can be customized by ane or more Jackson2ObjectMapperBuilderCustomizer beans. Such customizer beans tin can be ordered (Boot's ain customizer has an social club of 0), letting additional customization exist applied both before and later on Kicking's customization.

Any beans of type com.fasterxml.jackson.databind.Module are automatically registered with the automobile-configured Jackson2ObjectMapperBuilder and are applied to any ObjectMapper instances that it creates. This provides a global machinery for contributing custom modules when you add together new features to your application.

If you lot want to replace the default ObjectMapper completely, either define a @Edible bean of that type and mark it every bit @Chief or, if you prefer the builder-based approach, define a Jackson2ObjectMapperBuilder @Edible bean. Note that, in either case, doing then disables all auto-configuration of the ObjectMapper.

If you provide whatever @Beans of type MappingJackson2HttpMessageConverter, they replace the default value in the MVC configuration. Also, a convenience bean of type HttpMessageConverters is provided (and is always available if you apply the default MVC configuration). It has some useful methods to access the default and user-enhanced bulletin converters.

See the "Section 77.iv, "Customize the @ResponseBody Rendering"" section and the WebMvcAutoConfiguration source code for more details.

77.4 Customize the @ResponseBody Rendering

Spring uses HttpMessageConverters to return @ResponseBody (or responses from @RestController). You lot can contribute boosted converters past adding beans of the appropriate blazon in a Spring Kicking context. If a bean you add together is of a type that would have been included by default anyway (such as MappingJackson2HttpMessageConverter for JSON conversions), it replaces the default value. A convenience edible bean of type HttpMessageConverters is provided and is e'er available if yous use the default MVC configuration. Information technology has some useful methods to access the default and user-enhanced bulletin converters (For example, it can be useful if you want to manually inject them into a custom RestTemplate).

As in normal MVC usage, any WebMvcConfigurer beans that you provide can as well contribute converters past overriding the configureMessageConverters method. However, unlike with normal MVC, you can supply but additional converters that you need (because Spring Boot uses the same mechanism to contribute its defaults). Finally, if you opt out of the Jump Boot default MVC configuration by providing your own @EnableWebMvc configuration, you tin take command completely and do everything manually past using getMessageConverters from WebMvcConfigurationSupport.

See the WebMvcAutoConfiguration source code for more than details.

77.5 Handling Multipart File Uploads

Spring Boot embraces the Servlet 3 javax.servlet.http.Part API to back up uploading files. By default, Spring Kicking configures Spring MVC with a maximum size of 1MB per file and a maximum of 10MB of file information in a single asking. You lot may override these values, the location to which intermediate data is stored (for instance, to the /tmp directory), and the threshold past which information is flushed to deejay past using the properties exposed in the MultipartProperties grade. For instance, if y'all want to specify that files be unlimited, set the leap.servlet.multipart.max-file-size property to -1.

The multipart support is helpful when you lot desire to receive multipart encoded file data as a @RequestParam-annotated parameter of type MultipartFile in a Spring MVC controller handler method.

See the MultipartAutoConfiguration source for more details.

	Note
	Information technology is recommended to employ the container's built-in back up for multipart uploads rather than introducing an additional dependency such every bit Apache Eatables File Upload.

77.6 Switch Off the Spring MVC DispatcherServlet

By default, All content is served from the root of your awarding (/) down. If you would rather map to a unlike path, you tin configure one as follows:

            server.servlet.path=/elevation

If you have additional servlets you can declare a @Edible bean of blazon Servlet or ServletRegistrationBean for each and Spring Boot volition register them transparently to the container. Because servlets are registered that way, they tin can be mapped to a sub-context of the DispatcherServlet without invoking it.

Configuring the DispatcherServlet yourself is unusual but if you lot really need to practice it, a @Bean of type DispatcherServletPath must be provided also to provide the path of your custom DispatcherServlet.

77.vii Switch off the Default MVC Configuration

The easiest way to have complete control over MVC configuration is to provide your ain @Configuration with the @EnableWebMvc annotation. Doing so leaves all MVC configuration in your hands.

77.8 Customize ViewResolvers

A ViewResolver is a cadre component of Spring MVC, translating view names in @Controller to actual View implementations. Annotation that ViewResolvers are mainly used in UI applications, rather than Residual-style services (a View is non used to render a @ResponseBody). There are many implementations of ViewResolver to choose from, and Spring on its own is not opinionated about which ones you should utilize. Spring Kick, on the other hand, installs one or two for y'all, depending on what it finds on the classpath and in the application context. The DispatcherServlet uses all the resolvers it finds in the application context, trying each 1 in turn until it gets a event, and so, if you lot add your ain, you have to be aware of the order and in which position your resolver is added.

WebMvcAutoConfiguration adds the following ViewResolvers to your context:

• An InternalResourceViewResolver named 'defaultViewResolver'. This ane locates concrete resources that can be rendered past using the DefaultServlet (including static resource and JSP pages, if you use those). Information technology applies a prefix and a suffix to the view name and and so looks for a physical resources with that path in the servlet context (the defaults are both empty but are accessible for external configuration through leap.mvc.view.prefix and spring.mvc.view.suffix). You can override it past providing a bean of the same type.
• A BeanNameViewResolver named 'beanNameViewResolver'. This is a useful member of the view resolver chain and picks up whatever beans with the aforementioned name as the View being resolved. It should non be necessary to override or supersede it.
• A ContentNegotiatingViewResolver named 'viewResolver' is added simply if at that place are actually beans of type View nowadays. This is a 'master' resolver, delegating to all the others and attempting to find a match to the 'Accept' HTTP header sent by the client. In that location is a useful blog about ContentNegotiatingViewResolver that you lot might similar to report to acquire more than, and yous might also look at the source code for detail. You can switch off the machine-configured ContentNegotiatingViewResolver past defining a bean named 'viewResolver'.
• If you use Thymeleaf, you lot too take a ThymeleafViewResolver named 'thymeleafViewResolver'. It looks for resources by surrounding the view name with a prefix and suffix. The prefix is spring.thymeleaf.prefix, and the suffix is leap.thymeleaf.suffix. The values of the prefix and suffix default to 'classpath:/templates/' and '.html', respectively. Y'all tin can override ThymeleafViewResolver by providing a edible bean of the same name.
• If yous utilize FreeMarker, you likewise have a FreeMarkerViewResolver named 'freeMarkerViewResolver'. It looks for resources in a loader path (which is externalized to spring.freemarker.templateLoaderPath and has a default value of 'classpath:/templates/') by surrounding the view name with a prefix and a suffix. The prefix is externalized to leap.freemarker.prefix, and the suffix is externalized to spring.freemarker.suffix. The default values of the prefix and suffix are empty and '.ftl', respectively. You lot can override FreeMarkerViewResolver by providing a edible bean of the same name.
• If you use Groovy templates (actually, if groovy-templates is on your classpath), you too have a GroovyMarkupViewResolver named 'groovyMarkupViewResolver'. Information technology looks for resources in a loader path by surrounding the view name with a prefix and suffix (externalized to spring.nifty.template.prefix and spring.bully.template.suffix). The prefix and suffix have default values of 'classpath:/templates/' and '.tpl', respectively. You tin can override GroovyMarkupViewResolver past providing a edible bean of the same name.

For more than detail, meet the following sections:

• WebMvcAutoConfiguration
• ThymeleafAutoConfiguration
• FreeMarkerAutoConfiguration
• GroovyTemplateAutoConfiguration

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Source: https://docs.spring.io/spring-boot/docs/2.0.x/reference/html/howto-spring-mvc.html

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