groovy - 编译时使用groovy方法进行NPE

Question

我以一种奇怪的方式得到了 NPE。接下来是发生这种情况的方法调用:

    String exec(String command) {
        if (command == null || isConnected()) return null;

        Session session = null;
        boolean error = false;
        try {
            session = ssh.startSession();
//           try {
//                final Session.Command cmd = session.exec(command);
//                String result = cmd.getOutputAsString();
//                if (cmd.getExitStatus() != null && cmd.getExitStatus() != 0){
//                    //TODO:command execution failure should be logged
//                    error = true;
//                } else {
//                    return result;
//                }

//            } catch (Exception ex){
//                //TODO:command execution failure should be logged
//                ex.printStackTrace();
//                error = true;
//            }
        } catch (Exception ex) {
            // TODO:session creation failure should be logged
            ex.printStackTrace();
            error = true;
        } finally {
            session.close();
            if (error) return null;
        }
    }

如果我取消注释内部 try/catch block (甚至仅声明)，我会得到 groovy 生成的 NPE，如下所示:

java.lang.NullPointerException
    at org.objectweb.asm.MethodWriter.visitMaxs(Unknown Source)
    at org.objectweb.asm.MethodAdapter.visitMaxs(Unknown Source)
    at org.codehaus.groovy.classgen.AsmClassGenerator.visitConstructorOrMethod(AsmClassGenerator.java:605)
    at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitMethod(ClassCodeVisitorSupport.java:123)
    at org.codehaus.groovy.classgen.AsmClassGenerator.visitMethod(AsmClassGenerator.java:696)
    at org.codehaus.groovy.ast.ClassNode.visitContents(ClassNode.java:1039)
    at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitClass(ClassCodeVisitorSupport.java:50)
    at org.codehaus.groovy.classgen.AsmClassGenerator.visitClass(AsmClassGenerator.java:276)
    at org.codehaus.groovy.control.CompilationUnit$12.call(CompilationUnit.java:748)
    at org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:942)
    at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:519)
    at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:497)
    at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:474)
    at org.jetbrains.groovy.compiler.rt.GroovyCompilerWrapper.compile(GroovyCompilerWrapper.java:43)
    at org.jetbrains.groovy.compiler.rt.GroovycRunner.main(GroovycRunner.java:128)
    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.CommandLineWrapper.main(CommandLineWrapper.java:75)

代码没什么特别的，ssh变量不为空。但我不明白到底发生了什么。

Answer 1

看起来像是将 if (error) return null; 从 finally block 中放入方法 end 中就可以达到目的，但还不完全确定原因。