如何处理 Freemarker 字符串模板？

Question

我正在使用 Spring 使用 Freemarker 启动器启动。

给定以下字符串：

<h2>${fragment.title}</h2>

我正在尝试对此字符串执行一些验证以确保它包含正确的 Freemarker 语法。

我已尝试使用以下代码执行此操作：

@Autowired
private Configuration configuration;

private void validateTemplate(Fragment fragment) {

    try {

        ModelAndView model = new ModelAndView();
        model.addObject("fragment", fragment);

        StringTemplateLoader stringLoader = new StringTemplateLoader();
        stringLoader.putTemplate("template", fragment.getDesign());

        configuration.setTemplateLoader(stringLoader);
        configuration.setDefaultEncoding("UTF-8");

        Template template = configuration.getTemplate("template");
        template.process(model, new OutputStreamWriter(System.out));


    } catch (Exception e) {
        // failed validation...
    }

}

上面的字符串应该有效，因为 fragment 不为空。但是抛出以下错误：

2017-11-19 11:11:11.732 ERROR 4956 --- [-nio-443-exec-8] freemarker.runtime : Error executing FreeMarker template

freemarker.core.InvalidReferenceException: The following has evaluated to null or missing: ==> fragment [in template "template" at line 1, column 7]

---- Tip: If the failing expression is known to be 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. (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: ${fragment.title} [in template "template" at line 1, column 5] ---- at freemarker.core.InvalidReferenceException.getInstance(InvalidReferenceException.java:134) ~[freemarker-2.3.25-incubating.jar:2.3.25] at freemarker.core.UnexpectedTypeException.newDesciptionBuilder(UnexpectedTypeException.java:80) ~[freemarker-2.3.25-incubating.jar:2.3.25] at freemarker.core.UnexpectedTypeException.(UnexpectedTypeException.java:43) ~[freemarker-2.3.25-incubating.jar:2.3.25] at freemarker.core.NonHashException.(NonHashException.java:49) ~[freemarker-2.3.25-incubating.jar:2.3.25] at freemarker.core.Dot._eval(Dot.java:48) ~[freemarker-2.3.25-incubating.jar:2.3.25] at freemarker.core.Expression.eval(Expression.java:81) ~[freemarker-2.3.25-incubating.jar:2.3.25] at freemarker.core.DollarVariable.calculateInterpolatedStringOrMarkup(DollarVariable.java:96) ~[freemarker-2.3.25-incubating.jar:2.3.25] at freemarker.core.DollarVariable.accept(DollarVariable.java:59) ~[freemarker-2.3.25-incubating.jar:2.3.25] at freemarker.core.Environment.visit(Environment.java:327) [freemarker-2.3.25-incubating.jar:2.3.25] at freemarker.core.Environment.visit(Environment.java:333) [freemarker-2.3.25-incubating.jar:2.3.25] at freemarker.core.Environment.process(Environment.java:306) [freemarker-2.3.25-incubating.jar:2.3.25] at freemarker.template.Template.process(Template.java:386) [freemarker-2.3.25-incubating.jar:2.3.25]

我的设置中缺少什么导致 Freemarker 无法 'see' fragment？

Answer 1

获取Template对象本身就足以进行语法验证。根据应用程序的不同，验证模板是否会在运行时失败可能会相当棘手，因为您需要一个类似于真实事物的数据模型。

但我们假设您可以在您的案例中提供这样的数据模型。那么问题是 ModelAndView 不是你的模型。顾名思义，它是您的模型和视图。它只包含你的模型，在里面。（FreeMarker 不依赖于 Spring，因此只需将该对象用作通用 JavaBean，因此您的变量将是 ModeAndView 对象本身的 JavaBean 属性。）尝试传递 ModelAndView.getModel() 改为 Template.process。（我不是 100% 确定它是否总是显示所有模型变量，但我猜是这样。无论如何，它扩展了 FreeMarker 识别的 java.util.Map，并将使用 Map.get(varName) 来解析变量。 )

如何处理 Freemarker 字符串模板？

How to process Freemarker String template?

java

freemarker

use parenthesis: (myOptionalVar.foo)!myDefault, (myOptionalVar.foo)??