forked from spring-guides/gs-rest-service
-
Notifications
You must be signed in to change notification settings - Fork 0
/
README.disable_asc
174 lines (102 loc) · 9.1 KB
/
README.disable_asc
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
:project_id: gs-rest-service
:spring_version: 3.2.4.RELEASE
:spring_boot_version: 0.5.0.M4
:icons: font
:source-highlighter: prettify
This guide walks you through the process of creating a "hello world" link:/understanding/REST[RESTful web service] with Spring.
== What you'll build
You'll build a service that will accept HTTP GET requests at:
http://localhost:8080/greeting
and respond with a link:/understanding/JSON[JSON] representation of a greeting:
// Currently replacing json->javascript and groovy/gradle->java
[source,javascript]
----
{"id":1,"content":"Hello, World!"}
----
You can customize the greeting with an optional `name` parameter in the query string:
http://localhost:8080/greeting?name=User
The `name` parameter value overrides the default value of "World" and is reflected in the response:
// Currently replacing json->javascript and groovy/gradle->java
[source,javascript]
----
{"id":1,"content":"Hello, User!"}
----
== What you'll need
- About 15 minutes
include::macros/prereq_editor_jdk_buildtools.asc[]
include::macros/how_to_complete_this_guide.asc[]
[[scratch]]
== Set up the project
include::macros/build_system_intro.asc[]
include::macros/create_directory_structure_hello.asc[]
include::macros/create_both_builds.asc[]
include::macros/bootstrap_starter_pom_disclaimer.asc[]
[[initial]]
== Create a resource representation class
Now that you've set up the project and build system, you can create your web service.
Begin the process by thinking about service interactions.
The service will handle `GET` requests for `/greeting`, optionally with a `name` parameter in the query string. The `GET` request should return a `200 OK` response with JSON in the body that represents a greeting. It should look something like this:
// Currently replacing json->javascript and groovy/gradle->java
[source,javascript]
----
{
"id": 1,
"content": "Hello, World!"
}
----
The `id` field is a unique identifier for the greeting, and `content` is the textual representation of the greeting.
To model the greeting representation, you create a resource representation class. Provide a plain old java object with fields, constructors, and accessors for the `id` and `content` data:
.src/main/java/hello/Greeting.java
[source,java]
----
include::complete/src/main/java/hello/Greeting.java[]
----
NOTE: As you see in steps below, Spring uses the http://wiki.fasterxml.com/JacksonHome[Jackson JSON] library to automatically marshal instances of type `Greeting` into JSON.
Next you create the resource controller that will serve these greetings.
== Create a resource controller
In Spring's approach to building RESTful web services, HTTP requests are handled by a controller. These components are easily identified by the http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/stereotype/Controller.html[`@Controller`] annotation, and the `GreetingController` below handles `GET` requests for `/greeting` by returning a new instance of the `Greeting` class:
.src/main/java/hello/GreetingController.java
[source,java]
----
include::complete/src/main/java/hello/GreetingController.java[]
----
This controller is concise and simple, but there's plenty going on under the hood. Let's break it down step by step.
The `@RequestMapping` annotation ensures that HTTP requests to `/greeting` are mapped to the `greeting()` method.
NOTE: The above example does not specify `GET` vs. `PUT`, `POST`, and so forth, because `@RequestMapping` maps all HTTP operations by default. Use `@RequestMapping(method=GET)` to narrow this mapping.
`@RequestParam` binds the value of the query string parameter `name` into the `name` parameter of the `greeting()` method. This query string parameter is not `required`; if it is absent in the request, the `defaultValue` of "World" is used.
The implementation of the method body creates and returns a new `Greeting` object with `id` and `content` attributes based on the next value from the `counter`, and formats the given `name` by using the greeting `template`.
A key difference between a traditional MVC controller and the RESTful web service controller above is the way that the HTTP response body is created. Rather than relying on a link:/understanding/view-templates[view technology] to perform server-side rendering of the greeting data to HTML, this RESTful web service controller simply populates and returns a `Greeting` object. The object data will be written directly to the HTTP response as JSON.
To accomplish this, the http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/bind/annotation/ResponseBody.html[`@ResponseBody`] annotation on the `greeting()` method tells Spring MVC that it does not need to render the greeting object through a server-side view layer, but that instead that the greeting object returned _is_ the response body, and should be written out directly.
The `Greeting` object must be converted to JSON. Thanks to Spring's HTTP message converter support, you don't need to do this conversion manually. Because http://wiki.fasterxml.com/JacksonHome[Jackson 2] is on the classpath, Spring's http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/http/converter/json/MappingJackson2HttpMessageConverter.html[`MappingJackson2HttpMessageConverter`] is automatically chosen to convert the `Greeting` instance to JSON.
== Make the application executable
Although it is possible to package this service as a traditional link:/understanding/WAR[WAR] file for deployment to an external application server, the simpler approach demonstrated below creates a standalone application. You package everything in a single, executable JAR file, driven by a good old Java `main()` method. Along the way, you use Spring's support for embedding the link:/understanding/Tomcat[Tomcat] servlet container as the HTTP runtime, instead of deploying to an external instance.
.src/main/java/hello/Application.java
[source,java]
----
include::complete/src/main/java/hello/Application.java[]
----
The `main()` method defers to the http://docs.spring.io/spring-boot/docs/{spring_boot_version}/api/org/springframework/boot/SpringApplication.html[`SpringApplication`] helper class, providing `Application.class` as an argument to its `run()` method. This tells Spring to read the annotation metadata from `Application` and to manage it as a component in the link:/understanding/application-context[Spring application context].
The `@ComponentScan` annotation tells Spring to search recursively through the `hello` package and its children for classes marked directly or indirectly with Spring's http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/stereotype/Component.html[`@Component`] annotation. This directive ensures that Spring finds and registers the `GreetingController`, because it is marked with `@Controller`, which in turn is a kind of `@Component` annotation.
The http://docs.spring.io/spring-boot/docs/{spring_boot_version}/api/org/springframework/boot/autoconfigure/EnableAutoConfiguration.html[`@EnableAutoConfiguration`] annotation switches on reasonable default behaviors based on the content of your classpath. For example, because the application depends on the embeddable version of Tomcat (tomcat-embed-core.jar), a Tomcat server is set up and configured with reasonable defaults on your behalf. And because the application also depends on Spring MVC (spring-webmvc.jar), a Spring MVC http://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/servlet/DispatcherServlet.html[`DispatcherServlet`] is configured and registered for you — no `web.xml` necessary! Auto-configuration is a powerful, flexible mechanism. See the http://docs.spring.io/spring-boot/docs/{spring_boot_version}/api/org/springframework/boot/autoconfigure/EnableAutoConfiguration.html[API documentation] for further details.
include::macros/build_an_executable_jar_subhead.asc[]
include::macros/build_an_executable_jar_with_both.asc[]
:module: service
include::macros/run_the_application_with_both.asc[]
Logging output is displayed. The service should be up and running within a few seconds.
== Test the service
Now that the service is up, visit http://localhost:8080/greeting, where you see:
// Currently replacing json->javascript and groovy/gradle->java
[source,javascript]
----
{"id":1,"content":"Hello, World!"}
----
Provide a `name` query string parameter with http://localhost:8080/greeting?name=User. Notice how the value of the `content` attribute changes from "Hello, World!" to "Hello User!":
// Currently replacing json->javascript and groovy/gradle->java
[source,javascript]
----
{"id":2,"content":"Hello, User!"}
----
This change demonstrates that the `@RequestParam` arrangement in `GreetingController` is working as expected. The `name` parameter has been given a default value of "World", but can always be explicitly overridden through the query string.
Notice also how the `id` attribute has changed from `1` to `2`. This proves that you are working against the same `GreetingController` instance across multiple requests, and that its `counter` field is being incremented on each call as expected.
== Summary
Congratulations! You've just developed a RESTful web service with Spring.