Question

我第一次使用mvel。简单地运行TemplateRuntime.eval时，使用@includeNamed可以正常工作。

但是如果我尝试使用CompiledTemplate，它就会抛出一个NPE。难道我做错了什么？或者这是一个错误？我正在使用mvel 2.1.4.Final

public class App {
    public static void main(String[] args) {


        TemplateRegistry registry = new SimpleTemplateRegistry();
        registry.addNamedTemplate("world", TemplateCompiler.compileTemplate("world!!!"));

        System.out.println(TemplateRuntime.eval("Eval Hello: @includeNamed{'world'}", null, registry));

        CompiledTemplate ct = TemplateCompiler.compileTemplate("Compile Hello: @includeNamed{'world'}");
        System.out.println(TemplateRuntime.execute(ct, null, registry));
    }
}

堆栈跟踪（注意：Eval打印正常）：

Eval Hello: world!!!
Exception in thread "main" java.lang.NullPointerException
    at org.mvel2.integration.impl.StackResetResolverFactory.<init>(StackResetResolverFactory.java:15)
    at org.mvel2.compiler.CompiledExpression.getDirectValue(CompiledExpression.java:123)
    at org.mvel2.compiler.CompiledExpression.getValue(CompiledExpression.java:119)
    at org.mvel2.compiler.CompiledExpression.getValue(CompiledExpression.java:113)
    at org.mvel2.MVEL.executeExpression(MVEL.java:930)
    at org.mvel2.templates.res.CompiledNamedIncludeNode.eval(CompiledNamedIncludeNode.java:56)
    at org.mvel2.templates.res.TextNode.eval(TextNode.java:42)
    at org.mvel2.templates.res.TextNode.eval(TextNode.java:42)
    at org.mvel2.templates.TemplateRuntime.execute(TemplateRuntime.java:285)
    at org.mvel2.templates.TemplateRuntime.execute(TemplateRuntime.java:247)
    at org.mvel2.templates.TemplateRuntime.execute(TemplateRuntime.java:255)
    at org.mvel2.templates.TemplateRuntime.execute(TemplateRuntime.java:187)
    at mveltest.App.main(App.java:23)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

Answer 1

好吧，这似乎是一个错误。我注意到当调用variableResolverFactory.someMethod时，NPE发生在StackResetResolverFactory的构造函数中。

因此，作为一种解决方法，我使用带有VariableResolverFactory的execute方法。

Map<String, Object> dummyVariableMap = new HashMap<String, Object>();
VariableResolverFactory dummyResolverFactory = new SimpleVariableResolverFactory(dummyVariableMap);
System.out.println(TemplateRuntime.execute(ct, null, dummyResolverFactory, registry));

奇怪的是，我认为使用命名模板执行CompiledTemplate将是一个非常常见的用例。

mvel @includeNamed使用CompiledTemplate抛出NPE

1 个答案: