Groovy StreamingTemplateEngine异常缺少PropertyException

如何避免在映射中缺少模板参数时出现MissingPropertyException，并用null替换未找到的值

import groovy.text.StreamingTemplateEngine
import groovy.text.Template

class Test {

    private static Writable binding(Map map, String string) {
        Template template = new StreamingTemplateEngine().createTemplate(string)
        return template.make(map)
    }

    static void main(String... args) {
        def template = "\${test1} \${test2}"
        def map = ["test1": "test1"]
        print binding(map, template)
    }
}

---

没有用于抑制此异常的配置选项，但是可以扩展传递给模板的映射并稍微更改其行为。考虑下面的例子：

import groovy.text.StreamingTemplateEngine
import groovy.text.Template

def string = '''
Dear <% out.print firstname %> ${lastname},

We <% if (accepted) out.print 'are pleased' else out.print 'regret' %> 
to inform you that your paper entitled
'$title' was ${ accepted ? 'accepted' : 'rejected' }.

The conference committee.
'''

def map = [
    firstname: 'test',
    lastname: 'test',
    accepted: true
]

Template template = new StreamingTemplateEngine().createTemplate(string)
println template.make(map)

输出：

Dear test test,

We are pleased 
to inform you that your paper entitled
'null' was accepted.

The conference committee.

不再抛出

MissingPropertyException

。但是，如您所见，

null

在字符串中打印为

null

。如果要打印空字符串，可以将

Object get（Object key）

方法添加到

Bindings

并覆盖其默认行为：

class Bindings {
    @Delegate private final Map map

    Bindings(Map map) {
        this.map = map
    }

    boolean containsKey(Object key) {
        return true
    }

    Object get(Object key) {
        return map.getOrDefault(key, '')
    }
}

如果这样做，您将看到类似于以下内容的输出：

Dear test test,

We are pleased 
to inform you that your paper entitled
'' was accepted.

The conference committee.

---

希望有帮助。

作为替代方案，您可以使用groovy方法：

作为旁注，我写了一篇文章，作为对几年前其他模板引擎局限性的贡献和回应。很高兴看到它被使用

---

尽管事后看来这还远远不够完美。用一种更好的内部方法写另一本已经在我的清单上很久了

您应该提供一个可复制的示例。@MarmiteBomber您是对的，我添加了一个示例谢谢，地图包装器帮助了我哇，它帮助了我，节省了我很多时间，谢谢有没有办法保留默认值功能，如${myAbsentKey？：'defaultValue'}？因为使用此解决方案时，如果密钥不存在，则总是将其设置为null:'(

class Bindings {
    @Delegate private final Map map

    Bindings(Map map) {
        this.map = map
    }

    boolean containsKey(Object key) {
        return true
    }

    Object get(Object key) {
        return map.getOrDefault(key, '')
    }
}

Dear test test,

We are pleased 
to inform you that your paper entitled
'' was accepted.

The conference committee.

import groovy.text.StreamingTemplateEngine
import groovy.text.Template

def string = '''
Dear <% out.print firstname %> ${lastname},

We <% if (accepted) out.print 'are pleased' else out.print 'regret' %> 
to inform you that your paper entitled
'$title' was ${ accepted ? 'accepted' : 'rejected' }.

The conference committee.
'''

def map = [
    firstname: 'test',
    lastname: 'test',
    accepted: true
].withDefault { "<not found>" }

Template template = new StreamingTemplateEngine().createTemplate(string)
println template.make(map)

~> groovy test.groovy

Dear test test,

We are pleased
to inform you that your paper entitled
'<not found>' was accepted.

The conference committee.