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spring-mvc返回json数据

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在使用spring-mvc过程中遇到很多问题，记录下来方便查看

开发环境如下:

eclipse Oxygen Release (4.7.0)

java1.8

spring 4.3.3

freemarker 2.3.26(这个不是必须的)

maven依赖包如下：

<!-- spring mvc返回json所需依赖  -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.7.0</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.7.0</version>
    </dependency>
<!-- freemarker 引擎，有了这个就不需要使用jstl了，只需要使用freemarker表达式就行了 -->
    <dependency>
        <groupId>org.freemarker</groupId>
        <artifactId>freemarker</artifactId>
        <version>2.3.26-incubating</version>
    </dependency>
    <!-- spring 核心 -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>4.3.3.RELEASE</version>
    </dependency>
    <!-- springmvc 核心 -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>4.3.3.RELEASE</version>
    </dependency>
<!-- spring bean 核心 -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-beans</artifactId>
        <version>4.3.3.RELEASE</version>
    </dependency>
<dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context-support</artifactId>
        <version>4.3.3.RELEASE</version>
    </dependency>

web.xml 配置:

<servlet>
    <servlet-name>DispatcherServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>/WEB-INF/applicationContext.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup><!--启动顺序，让这个Servlet随Servletp容器一起启动。 -->
</servlet>
<servlet-mapping>
    <servlet-name>DispatcherServlet</servlet-name>
    <url-pattern>/</url-pattern> <!--会拦截URL中带“/”的请求。 -->
</servlet-mapping>

spring-mvc配置:

<mvc:annotation-driven />
<context:component-scan base-package="canxing.web" />

spring-mvc配置freemarker:

<!-- freemarker 配置文件 -->
<!-- freemarker config -->
<bean id="freemarkerConfig"
    class="org.springframework.web.servlet.view.freemarker.FreeMarkerConfigurer">
    <property name="templateLoaderPath" value="/WEB-INF/freemarker/" />
</bean>

<!-- View resolvers can also be configured with ResourceBundles or XML files.
    If you need different view resolving based on Locale, you have to use the
    resource bundle resolver. -->
<bean id="viewResolver"
    class="org.springframework.web.servlet.view.freemarker.FreeMarkerViewResolver">
    <property name="cache" value="true" />
    <property name="prefix" value="" />
    <property name="suffix" value=".ftl" />
</bean>

JSONController.java:

@Controller
public class JSONController {
    @RequestMapping(path="/json",produces="application/json")
    public @ResponseBody User index() {//使用@RespnseBody将返回的对象转化为JSON数据
        System.out.println("index start");
        User user = new User();
        user.setUsername("canxing");
        user.setPassword("123");
        System.out.println("index end");
        return user;
    }
    @RequestMapping(path="/")
    public String test() {
        return "test";
    }
}

User.java：

//类不需要进行处理，只是一个普通的pojo类
public class User{
        private String username;
        private String password;
        public String getUsername() {
            return username;
        }
        public void setUsername(String username) {
            this.username = username;
        }
        public String getPassword() {
            return password;
        }
        public void setPassword(String password) {
            this.password = password;
        }
        @Override
        public String toString() {
            return "User [username=" + username + ", password=" + password + "]";
        }
    }

test.flt:

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<html>
	<head>
		<title>freemarker test </title>
		<script type="text/javascript">
			function loadXMLDoc()
			{
				xmlhttp=null;
				if (window.XMLHttpRequest)
				  {// code for Firefox, Mozilla, IE7, etc.
				  xmlhttp=new XMLHttpRequest();
				  }
				else if (window.ActiveXObject)
				  {// code for IE6, IE5
				  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
				  }
				if (xmlhttp!=null)
				  {
				  xmlhttp.onreadystatechange=state_Change;
				  xmlhttp.open("GET","http://localhost:8080/spring_web_test/json",true);
				  xmlhttp.send(null);
				  }
				else
				  {
				  alert("Your browser does not support XMLHTTP.");
				  }
			}
			function state_Change(){
				var obj = eval("(" + xmlhttp.responseText + ")");
				document.getElementById("username").innerHTML=obj.username
				document.getElementById("password").innerHTML=obj.password
			}
      </script>
	</head>
	<body>
		<h1>freemarker test</h1>
		username : <span id='username'></span><br>
		password : <span id='password'></span><br>
		<button type='button' onclick="loadXMLDoc()">adfads</button>
	</body>
</html>

spring-mvc返回JSOn数据参考源码

寻找答案中遇到的问题

  1. 依赖问题，spring 默认的对象转化为 json 的 jar 包依赖，网上多是直接使用并没有说明依赖
  2. 还是依赖问题，spring 和 jackson 之间版本的兼容性太差，稍微更改以下 jackson 或者 spring 的版本就会导致 NoSuchMethodError 错误，据说这里可以看见版本支持，但是看不懂