This guide walks you through the process of creating a "hello world" web site 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 web page displaying a greeting:
"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:
"Hello, User!"
What you’ll need
-
About 15 minutes
-
A favorite text editor or IDE
-
JDK 1.6 or later
-
You can also import the code from this guide as well as view the web page directly intoSpring
Tool Suite (STS) and work your way through it from there.
How to complete this guide
Like most Spring Getting Started guides, you can start from scratch and
complete each step, or you can bypass basic setup steps that are already familiar to you. Either way, you end up with working code.
To start from scratch, move on to Set
up the project.
To skip the basics, do the following:
-
Download and unzip the
source repository for this guide, or clone it using Git:git
clone https://github.com/spring-guides/gs-serving-web-content.git -
cd into
gs-serving-web-content/initial -
Jump ahead to Create a web controller.
When you’re finished, you can check your results against the code ings-serving-web-content/complete.
Set up the project
First you set up a basic build script. You can use any build system you like when building apps with Spring, but the code you need to work with Gradle and Maven is
included here. If you’re not familiar with either, refer to Building Java Projects with Gradle or Building
Java Projects with Maven.
Create the directory structure
In a project directory of your choosing, create the following subdirectory structure; for example, with mkdir on *nix systems:
-p src/main/java/hello
└── src
└── main
└── java
└── hello
Create a Gradle build file
Below is the initial
Gradle build file. But you can also use Maven. The pom.xml file is includedright here.
If you are using Spring Tool Suite (STS), you can import the guide directly.
build.gradle
buildscript {
repositories {
maven { url "http://repo.spring.io/libs-release" }
mavenLocal()
mavenCentral()
}
dependencies {
classpath("org.springframework.boot:spring-boot-gradle-plugin:1.1.2.RELEASE")
}
}
apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: 'spring-boot'
jar {
baseName = 'gs-serving-web-content'
version = '0.1.0'
}
repositories {
mavenLocal()
mavenCentral()
maven { url "http://repo.spring.io/libs-release" }
}
dependencies {
compile("org.springframework.boot:spring-boot-starter-thymeleaf")
testCompile("junit:junit")
}
task wrapper(type: Wrapper) {
gradleVersion = '1.11'
}The Spring
Boot gradle plugin provides many convenient features:
-
It collects all the jars on the classpath and builds a single, runnable "über-jar", which makes it more convenient to execute and transport your service.
-
It searches for the
publicmethod to flag as a runnable class.
static void main() -
It provides a built-in dependency resolver that sets the version number to match Spring
Boot dependencies. You can override any version you wish, but it will default to Boot’s chosen set of versions.
Create a web controller
In Spring’s approach to building web sites, HTTP requests are handled by a controller. You can easily identify these requests by the @Controller annotation.
In the following example, the GreetingController handles GET requests for /greeting by returning the name of a View,
in this case, "greeting". A View is
responsible for rendering the HTML content:
src/main/java/hello/GreetingController.java
package hello;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
@Controller
public class GreetingController {
@RequestMapping("/greeting")
public String greeting(@RequestParam(value="name", required=false, defaultValue="World") String name, Model model) {
model.addAttribute("name", name);
return "greeting";
}
}This controller is concise and simple, but there’s plenty going on. Let’s break it down step by step.
The @RequestMapping annotation
ensures that HTTP requests to /greeting are
mapped to the greeting() method.
The above example does not specify GET vs. PUT, POST,and so forth, because @RequestMapping mapsall HTTP operations by default. Use @RequestMapping(method=GET) tonarrow this mapping. |
@RequestParam binds
the value of the query String parameter name into
the nameparameter 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 value of the nameparameter
is added to a Model object,
ultimately making it accessible to the view template.
The implementation of the method body relies on a view
technology, in this case Thymeleaf, to perform server-side rendering of the HTML. Thymeleaf parses the greeting.htmltemplate
below and evaluates the th:text expression
to render the value of the ${name}parameter
that was set in the controller.
src/main/resources/templates/greeting.html
<!DOCTYPE HTML>
<html xmlns:th="http://www.thymeleaf.org">
<head>
<title>Getting Started: Serving Web Content</title>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body>
<p th:text="'Hello, ' + ${name} + '!'" />
</body>
</html>Make the application executable
Although it is possible to package this service as a traditional 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 Tomcatservlet container as the HTTP runtime, instead of deploying to an external
instance.
src/main/java/hello/Application.java
package hello;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.SpringApplication;
import org.springframework.context.annotation.ComponentScan;
@ComponentScan
@EnableAutoConfiguration
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}The main() method
defers to the SpringApplication helper
class, providingApplication.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 Spring application context.
The @ComponentScan annotation
tells Spring to search recursively through the hellopackage
and its children for classes marked directly or indirectly with Spring’s @Componentannotation.
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 @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 DispatcherServlet is
configured and registered for you — no web.xml necessary!
Auto-configuration is a powerful, flexible mechanism. See the API
documentation for further details.
Build an executable JAR
You can build a single executable JAR file that contains all the necessary dependencies, classes, and resources. This makes it easy to ship, version, and deploy the service as an
application throughout the development lifecycle, across different environments, and so forth.
Then you can run the JAR file:
If you are using Maven, you can run the application using mvn. Or you can build the JAR file with
spring-boot:runmvn and run the JAR by typing:
clean package
| The procedure above will create a runnable JAR. You can also opt to build a classic WAR file instead. |
Run the service
If you are using Gradle, you can run your service at the command line this way:
If you are using Maven, you can run your service by typingmvn. |
You can alternatively run the app directly from Gradle like this:
With mvn, you can run mvn. |
Logging output is displayed. The service should be up and running within a few seconds.
Test the service
Now that the web site is running, visit http://localhost:8080/greeting,
where you see:
"Hello, World!"
Provide a name query
string parameter with http://localhost:8080/greeting?name=User. Notice how the message changes from "Hello, World!" to "Hello, User!":
"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.
Summary
Congratulations! You have just developed a web page using Spring.
整个例子, 用maven 和gradle 分别试了一下, 感觉 gradle 更加简洁一些.
Gradle果然是利器. 而且这个例子里面, 可执行jar 来运行spring 的例子, 也是设计精巧,令人赞叹.