freemarker学习 （servlet + freemarker -> Struts2+freemarker -> springMVC+freemarker）

 <dependency>
            <groupId>org.freemarker</groupId>
            <artifactId>freemarker</artifactId>
            <version>2.3.23</version>
        </dependency>

public class TestFreemarker {
    public static void main(String[] args) throws Exception{

        //1、创建Freemark配置实例
        Configuration cfg = new Configuration();
        cfg.setDirectoryForTemplateLoading(new File("template"));

        //2、创建数据模型
        Map root = new HashMap();
        root.put("user", "老高");
        root.put("random",  new Random().nextInt(100));
        List<Address> addressList = new ArrayList<Address>();
        addressList.add(new Address("中国", "北京"));
        addressList.add(new Address("法国", "巴黎"));
        root.put("addressList", addressList);

        //3、加载模板文件
        Template template = cfg.getTemplate("scope.ftl");

        //4、显示生成的数据
        Writer out = new OutputStreamWriter(System.out);
        template.process(root, out);
        out.flush();
        out.close();
    }
}

<servlet>
        <servlet-name>freemarker</servlet-name>
        <servlet-class>
            freemarker.ext.servlet.FreemarkerServlet
        </servlet-class>
        <!--下面的配置freemarke的ftl文件的位置 -->
        <init-param>
            <param-name>TemplatePath</param-name>
            <param-value>/WEB-INF/template</param-value>
        </init-param>
        <!-- 是否和服务器（tommcat)一起启动。-->
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>freemarker</servlet-name>
        <url-pattern>*.ftl</url-pattern>
    </servlet-mapping>

  <action name="userAction" class="com.zhen.struts2freemarker.action.UserAction">
            <result name="success"  type="freemarker">/WEB-INF/template/user_show.ftl</result>
        </action>

    @Bean
    public FreeMarkerConfigurer freeMarkerConfigurer(){
        FreeMarkerConfigurer freeMarkerConfigurer = new FreeMarkerConfigurer();
        freeMarkerConfigurer.setDefaultEncoding("UTF-8");
        freeMarkerConfigurer.setTemplateLoaderPath("/");
        return freeMarkerConfigurer;
    }

    @Override
    public void configureViewResolvers(ViewResolverRegistry registry) {
        //spring4 默认不是freemarker，而是Thymeleaf
        FreeMarkerViewResolver freeMarkerViewResolver = new FreeMarkerViewResolver();
        freeMarkerViewResolver.setPrefix("/WEB-INF/view");
        freeMarkerViewResolver.setSuffix(".ftl");
        freeMarkerViewResolver.setCache(false);//cache最好配置为false，否则再次去缓存如果与request有关则gg
        //这行一定要配置，不然容易中文乱码，默认的charset是ISO-8859-1
        freeMarkerViewResolver.setContentType("text/html;charset=UTF-8");
        registry.viewResolver(freeMarkerViewResolver);
        registry.freeMarker();
    }

1、java.lang.ClassNotFoundException: org.springframework.ui.freemarker.FreeMarkerConfigurationFactory
    首先怀疑是freemarker少了什么支持包
    freemarker版本更换试试无效
    打开freemarker包源文件，没发现对应支持spring的类与包，则判断支持类由spring提供，则依次打开spring-webmvc、web、context，发现只有context里面有ui这个文件夹，且里面没有freemarker文件夹，则知道是缺少了context-support这个补充包

2、org.springframework.beans.factory.BeanInitializationException: In addition to a FreeMarker view resolver there must also be a single FreeMarkerConfig bean in this web application context (or its parent): FreeMarkerConfigurer is the usual implementation. This bean may be given any name.
      at org.springframework.web.servlet.config.annotation.ViewResolverRegistry.freeMarker(ViewResolverRegistry.java:183)
    这个首先自己理解：
        以为是freemarker解析器没给名字，于是瞎setViewName了一下，无效，记得mvc的setViewName是设置一些默认的页面链接
    把错误翻译一下：
        是freemarker的解析器必须需要一个freemarker的配置器，配置器的Bean我没有提供，因为freemarker不是mvc的默认支持部分，所以配置默认没有
    补充一下freemarker配置即可：
         @Bean
            public FreeMarkerConfigurer freeMarkerConfigurer(){
                FreeMarkerConfigurer freeMarkerConfigurer = new FreeMarkerConfigurer();
                freeMarkerConfigurer.setDefaultEncoding("UTF-8");
                return freeMarkerConfigurer;
            }

3、No mapping found for HTTP request with URI [/springMVC_freemarker/base/testFreemarker] in DispatcherServlet with name ‘servletDispatcher‘
    初步怀疑是springmvc没扫描到controller
    解决方案：
        @ComponentScan("com.zhen.springmvc_freemarker")
4、Servlet.service() for servlet [servletDispatcher] in context with path [/springMVC_freemarker] threw exception [Could not resolve view with name ‘test_freemarker‘ in servlet with name ‘servletDispatcher‘] with root cause
  javax.servlet.ServletException: Could not resolve view with name ‘test_freemarker‘ in servlet with name ‘servletDispatcher‘
      at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1237)
      at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1037)
      at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:980)
      at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
      at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
      at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
      初步怀疑是配置的解析器的前后缀无效
        往return地址的地方写全依旧无效
    怀疑是解析器配置得有问题，没有将对应文件当成freemarker处理，则增加freemarkerConfigurer的baseTemplatePath解决
        freeMarkerConfigurer.setTemplateLoaderPath("/WEB-INF/view");

5、freemarker出现中文乱码
    1、是否是对应的html里面没有设置
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        加上这句，没啥用
    2、百度得知freemarkerViewResource还要配置一下contentType设置下response的类型和编码，于是增加：
        registry.freeMarker()得到的对象没有设置contentType方法，因此自定义进去，改为：
            @Override
            public void configureViewResolvers(ViewResolverRegistry registry) {
                //spring4 默认不是freemarker，而是Thymeleaf
                FreeMarkerViewResolver freeMarkerViewResolver = new FreeMarkerViewResolver();
                freeMarkerViewResolver.setPrefix("/WEB-INF/view");
                freeMarkerViewResolver.setSuffix(".ftl");
                freeMarkerViewResolver.setCache(false);//cache最好配置为false，否则再次去缓存如果与request有关则gg
                //这行一定要配置，不然容易中文乱码，默认的charset是ISO-8859-1
                freeMarkerViewResolver.setContentType("text/html;charset=UTF-8");
                registry.viewResolver(freeMarkerViewResolver);
            }
    然后一直报错找不到视图：test_freemarker
    怀疑是解析器没有执行，没有进行封装view，于是解析器解析方法打断点，发现成功封装了view，那么为什么找不到视图呢？
    断点freemarker找视图的方法，发现那里传入我认为的正确的视图url找不到，检查class编译后文件感觉还没错
    回退到乱码前配置，断点看下找视图的地方，发现传入的url不是/WEB-INF/view/test_freemarker.ftl而是test_freemarker.ftl，发现contentType中的编码为iso-8859-1
    回到我的配置地方，认真一看：
        registry.freeMarker(); //这样配置的视图解析器
        @Bean
        public FreeMarkerConfigurer freeMarkerConfigurer(){
            FreeMarkerConfigurer freeMarkerConfigurer = new FreeMarkerConfigurer();
            freeMarkerConfigurer.setDefaultEncoding("UTF-8");
            freeMarkerConfigurer.setTemplateLoaderPath("/WEB-INF/view");
            return freeMarkerConfigurer;
        }
        原来freemarker configure中设置的模板基础路径是/WEB-INF/view,所以我传入/WEB-INF/view/test_freemarker.ftl找不到，于是更改为：freeMarkerConfigurer.setTemplateLoaderPath("/"); 问题解决