springboot整合freemarker的踩坑及解決

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springboot整合freemarker踩坑

報錯

2021-04-23 02:01:18.148 ERROR 9484 — [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is freemarker.core.InvalidReferenceException: The following has evaluated to null or missing:
==> hots  [in template "inc/right.ftl" at line 6, column 11]

—-
Tip: If the failing expression is known to legally refer to something that's sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??
—-

—-
FTL stack trace ("~" means nesting-related):
    – Failed at: @hots  [in template "inc/right.ftl" at line 6, column 9]
    – Reached through: #include "/inc/right.ftl"  [in template "index.ftl" at line 52, column 13]
    ~ Reached through: #nested  [in template "inc/layout.ftl" in macro "layout" at line 25, column 5]
    ~ Reached through: @layout "首頁"  [in template "index.ftl" at line 2, column 1]
—-] with root cause

freemarker.core.InvalidReferenceException: The following has evaluated to null or missing:
==> hots  [in template "inc/right.ftl" at line 6, column 11]

—-
Tip: If the failing expression is known to legally refer to something that's sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??
—-

—-
FTL stack trace ("~" means nesting-related):
    – Failed at: @hots  [in template "inc/right.ftl" at line 6, column 9]
    – Reached through: #include "/inc/right.ftl"  [in template "index.ftl" at line 52, column 13]
    ~ Reached through: #nested  [in template "inc/layout.ftl" in macro "layout" at line 25, column 5]
    ~ Reached through: @layout "首頁"  [in template "index.ftl" at line 2, column 1]
—-
    at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:134) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.UnifiedCall.accept(UnifiedCall.java:106) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.Environment.visit(Environment.java:330) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.Environment.visit(Environment.java:336) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.Environment.include(Environment.java:2582) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.Include.accept(Include.java:171) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.Environment.visit(Environment.java:366) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.Environment.invokeNestedContent(Environment.java:618) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.BodyInstruction.accept(BodyInstruction.java:60) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.Environment.visit(Environment.java:366) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.Environment.invoke(Environment.java:775) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.UnifiedCall.accept(UnifiedCall.java:83) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.Environment.visit(Environment.java:330) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.Environment.visit(Environment.java:336) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.core.Environment.process(Environment.java:309) ~[freemarker-2.3.28.jar:2.3.28]
    at freemarker.template.Template.process(Template.java:384) ~[freemarker-2.3.28.jar:2.3.28]
    at org.springframework.web.servlet.view.freemarker.FreeMarkerView.processTemplate(FreeMarkerView.java:389) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.view.freemarker.FreeMarkerView.doRender(FreeMarkerView.java:302) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.view.freemarker.FreeMarkerView.renderMergedTemplateModel(FreeMarkerView.java:253) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.view.AbstractTemplateView.renderMergedOutputModel(AbstractTemplateView.java:178) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:316) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1370) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1116) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1055) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1005) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:897) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:882) ~[spring-webmvc-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:834) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1417) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) ~[na:na]
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) ~[na:na]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.14.jar:9.0.14]
    at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]

2021-04-23 02:01:18.177 ERROR 9484 — [nio-8080-exec-1] s.e.ErrorMvcAutoConfiguration$StaticView : Cannot render error page for request [/] and exception [The following has evaluated to null or missing:
==> hots  [in template "inc/right.ftl" at line 6, column 11]

—-
Tip: If the failing expression is known to legally refer to something that's sometimes null or missing, either specify a default value like myOptionalVar!myDefault, or use <#if myOptionalVar??>when-present<#else>when-missing</#if>. (These only cover the last step of the expression; to cover the whole expression, use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??
—-

—-
FTL stack trace ("~" means nesting-related):
    – Failed at: @hots  [in template "inc/right.ftl" at line 6, column 9]
    – Reached through: #include "/inc/right.ftl"  [in template "index.ftl" at line 52, column 13]
    ~ Reached through: #nested  [in template "inc/layout.ftl" in macro "layout" at line 25, column 5]
    ~ Reached through: @layout "首頁"  [in template "index.ftl" at line 2, column 1]
—-] as the response has already been committed. As a result, the response may have the wrong status code.

在這裡插入圖片描述

問題原因

因為在service裡試著把redis邏輯代碼運行，然後再控制臺上輸出，結果發現結果是沒有問題的，而且通過報錯信息初步認為是前端的問題，hots沒找到，但是跟之前的一個類似功能相比較，然後通過不斷的對比，找到問題是出在配置類。

之前一直認為template類中的getname方法就能完成映射功能

在這裡插入圖片描述

其實需要在FreemarkerConfig類裡面進行聲明

解決方法

再FreemarkerConfig類先通過@Autowired導入template類，然後使用configuration.setSharedVariable(“hots”, hotsTemplate);進行聲明，缺少這一步會使得前端對於<@hots>這個標簽無法識別。

springboot freemarker基礎配置及使用

1.基礎配置

1.1引入依賴

<!-- 引入freemarker模板引擎的依賴 -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-freemarker</artifactId>
</dependency>

1.2在application.properties配置文件中添加如下配置：

# 是否開啟thymeleaf緩存,本地為false，生產建議為true
spring.freemarker.cache=false
spring.freemarker.charset=UTF-8
spring.freemarker.allow-request-override=false
spring.freemarker.check-template-location=true
#類型
spring.freemarker.content-type=text/html
spring.freemarker.expose-request-attributes=true
spring.freemarker.expose-session-attributes=true
#
#文件後綴
spring.freemarker.suffix=.ftl
#路徑 .ftl文件就創建在templates下面或者子目錄
spring.freemarker.template-loader-path=classpath:/templates/

2.基礎使用

首先我在controller類中編寫一個測試接口用來測試使用，編寫內容如下

@Controller
public class FreeMarkerController {

    Map<String ,Object> map = new HashMap<>();
    List<Object> list = new ArrayList();
    @GetMapping("/freemaker/{id}/{name}")
    public String demo(@PathVariable("id")String id ,@PathVariable("name") String name,Model model){

        map.clear();
        map.put("id",id);
        map.put("name",name);
        list.add(2);
        list.add(4);
        map.put("aa",null);
        model.addAttribute("map",map);
        model.addAttribute("list",list);
        model.addAttribute("date",new Date());
        return "index";
    }
}

以下所有變量都是有上面接口提供

2.1調用map類型數據,實體類也可使用此格式調用屬性

/*可直接獲取id對應的v值*/
id:${map.id}
name:${map.name}

2.2集合調用，set集合也可用此格式調用相應的元素

list01:${list[0]}
list02:${list[1]}

2.3字符串拼接的兩種方法

${"你好啊${map.name}"}
${"你好啊"+map.name}

2.4FreeMarker表達式中支持“+”、“－”、“*”、“/”、“%”運算符

${list[1]+list[0]}
${list[1]-list[0]}
${list[1]*list[0]}
${list[1]/list[0]}
${list[1]%list[0]}

2.5表達式中支持的比較運算符有如下幾種：

1. =（或者==）：判斷兩個值是否相等；
2. !=：判斷兩個值是否不相等；
註： =和!=可以用作字符串、數值和日期的比較，但兩邊的數據類型必須相同。而且FreeMarker的比較是精確比較，不會忽略大小寫及空格。
3. >（或者gt）：大於
4. >=（或者gte）：大於等於
5. <（或者lt）：小於
6. <=（或者lte）：小於等於
註： 上面這些比較運算符可以用於數字和日期，但不能用於字符串。大部分時候，使用gt比>有更好的效果，因為FreeMarker會把>解釋成標簽的結束字符。可以使用括號來避免這種

2.6時間格式轉換

${date?string("yyyy-MM-dd")}

2.7支持邏輯表達式

FreeMarker支持邏輯運算但是隻支持佈爾型邏輯運算兩個值進行比較運算的的時候需要添加括號才能進行邏輯運算,一般用於指令中

FreeMarker支持邏輯運算但是隻支持佈爾型邏輯運算兩個值進行比較運算的的時候需要添加括號才能進行邏輯運算,一般用於指令中
1. &&： 邏輯與；
2. ||：邏輯或；
3. !：邏輯非
邏輯運算符隻能用於佈爾值。

2.8FreeMarker無法理解null值

FreeMarker的變量必須賦值，否則就會拋出異常。而對於FreeMarker來說，null值和不存在的變量是完全一樣的，因為FreeMarker無法理解null值。
FreeMarker提供兩個運算符來避免空值：
1.!運算
1.1若是msg不存在不報異常默認空值，若是不使用！會報異常<br>
${msg!}
1.2若是存在則輸出，若是不存在則默認為abc<br>
${map.a!"abc"}<br>
2.？？返回佈爾值一般用在指令中下面會有引用此處不解釋<br>

2.9 if指令

<#if map.aa?? >
    存在
    <#else >
    不存在
</#if>
<br>
<#if (list[0]>=3) >
    優秀
    <#elseif (list[0]>=2)>
    良好
    <#else >
    差勁
</#if>

2.10 list指令 遍歷

<#list list as li>
    ${li}<br>
</#list>

以上為個人經驗，希望能給大傢一個參考，也希望大傢多多支持WalkonNet。

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