5分钟用Spring4 搭建一个REST WebService

前置技能

① 使用maven来管理java项目

这个技能必须点一级，以便快速配置项目。

本文实际上是我学习Spring的过程中搬的官网上的demo，使用maven配置项目。

② jdk 1.8+   该服务demo需要在jdk1.8+的环境下运行

新建项目，配置依赖文件

① 安装好eclipse的maven插件后，使用file——new——other——maven——maven project 新建一个空的maven项目。

② 访问Spring官网demo http://spring.io/guides/gs/rest-service/

将Build With Maven 模块中提供的pom内容复制到我们自己的pom文件中，注意将项目坐标替换成上图中的配置。

最终得到pom文件：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.sogou.testspring</groupId>
  <artifactId>testspring-demo</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.2.5.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
    </dependencies>

    <properties>
        <java.version>1.8</java.version>
    </properties>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
    <repositories>
        <repository>
            <id>spring-milestone</id>
            <url>https://repo.spring.io/libs-release</url>
        </repository>
    </repositories>
    <pluginRepositories>
        <pluginRepository>
            <id>spring-milestone</id>
            <url>https://repo.spring.io/libs-release</url>
        </pluginRepository>
    </pluginRepositories>
</project>

编写Model和Controller

在source目录 src/main/java下新建hello包，在hello包下新建

① Greeting.java

package hello;

public class Greeting {

    private final long id;
    private final String content;

    public Greeting(long id, String content) {
        this.id = id;
        this.content = content;
    }

    public long getId() {
        return id;
    }

    public String getContent() {
        return content;
    }
}

② GreetingController.java

package hello;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.atomic.AtomicLong;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class GreetingController {

    private static final String template = "Hello, %s!";
    private final AtomicLong counter = new AtomicLong();

    @RequestMapping("/greeting")
    public Greeting greeting(@RequestParam(value="name", defaultValue="World") String name) {
        return new Greeting(counter.incrementAndGet(),
                            String.format(template, name));
    }
    @RequestMapping(value="/greeting2")
    public String Greeting2(@RequestParam(value="name",defaultValue="meiyou") String name){
        return name;
    }
    @RequestMapping("/greeting3")
    public List<Greeting> greeting3(@RequestParam(value="name", defaultValue="World") String name) {
        List<Greeting> list=new ArrayList<Greeting>();
        list.add(new Greeting(counter.incrementAndGet(),
                String.format(template, name)));
        list.add(new Greeting(counter.incrementAndGet(),
                String.format(template, name)));
        return list;
    }
}

③ 启动服务  Application.java

package hello;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

官网的demo至此为止，可以发现这个demo并不需要配置web.xml或者spring dispatherServlet的xml文件，也需要依赖web容器就可以运行。 看起来这更像是一个普通的Java应用程序。

启动服务&访问

① 因为在pom中配置了插件

 <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>

所以我们可以直接 runAs——maven build，target输入 spring-boot:run  来启动服务

② 通过maven package打包项目，生成jar包，然后在target目录下  java -jar  jar包名称，即可启动项目

但是

原搬原官网的demo，启动的时候会报错，顺着报错信息找下去，发现

spring-boot-autoconfigure-1.2.5.RELEASE.jar包下

org.springframework.boot.autoconfigure.thymeleaf.ThymeleafProperties 类中

有这么一段代码

public static final String DEFAULT_PREFIX = "classpath:/templates/";

public static final String DEFAULT_SUFFIX = ".html";

看样子需要一个templates的目录，于是在resources目录下新建一个templates目录，再次启动成功。

在浏览器中访问：

http://localhost:8080/greeting

{"id":2,"content":"Hello, World!"}

http://localhost:8080/greeting2
meiyou

http://localhost:8080/greeting3
[{"id":3,"content":"Hello, World!"},{"id":4,"content":"Hello, World!"}]

其他

注意到demo的控制器中使用了一个注解 @RestController ，这个在spring3.x里边是没有的。

/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.bind.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.stereotype.Controller;

/**
 * A convenience annotation that is itself annotated with {@link Controller @Controller}
 * and {@link ResponseBody @ResponseBody}.
 * <p>
 * Types that carry this annotation are treated as controllers where
 * {@link RequestMapping @RequestMapping} methods assume
 * {@link ResponseBody @ResponseBody} semantics by default.
 *
 * @author Rossen Stoyanchev
 * @author Sam Brannen
 * @since 4.0
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Controller
@ResponseBody
public @interface RestController {

    /**
     * The value may indicate a suggestion for a logical component name,
     * to be turned into a Spring bean in case of an autodetected component.
     * @return the suggested component name, if any
     * @since 4.0.1
     */
    String value() default "";

}

可以看到该注解是一个类注解，其功能相当于同时应用了  @Controller 和 @ResponseBody