我有这个类层次结构
学生类.java
public class StudentClass {
private List<Student> studentList;
public List<Student> getStudentList() {
return studentList;
}
public void setStudentList(List<Student> studentList) {
this.studentList = studentList;
}
}
学生.java
public class Student {
private Child child;
private int studAge;
public Student(Child child, int studAge) {
this.child = child;
this.studAge = studAge;
}
public Child getChild() {
return child;
}
public void setChild(Child child) {
this.child = child;
}
public int getStudAge() {
return studAge;
}
public void setStudAge(int studAge) {
this.studAge = studAge;
}
}
子.java
public class Child {
private String name;
private int age;
public Child(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
主班
通过一些逻辑，我构建了这个表达式来执行MVEL。这段代码在为 null时工作正常child2，但当为 null时，child1它会给出以下错误。这是一个有效的场景，它只是我的应用程序中我的实体的副本。Child 可能在 Parent 中为 null。
仅当对象在索引 0 处为空时才会出现问题，其余所有索引都可以正常工作，即使在索引 1 处为空，并且如果条件索引 0 失败，则它将在索引 2 处执行
public class MvelTest {
public static void main(String args[]) throws Exception {
String s = "if(contextObjectStudentClass.?studentList != null ){ foreach ( loopVariable0 : contextObjectStudentClass.?studentList){if ( loopVariable0.?child.?age==21 ){return loopVariable0.?child.?name ;}}}return null ;";
Child child2 = new Child("ankur", 23);
Child child1 = null;
Child child3 = new Child("ankurs", 21);
Student s1 = new Student(child1, 21);
Student s2 = new Student(child2, 23);
Student s3 = new Student(child3, 27);
List<Student> studentList = new ArrayList<Student>();
studentList.add(s1);
studentList.add(s2);
studentList.add(s3);
StudentClass class1 = new StudentClass();
class1.setStudentList(studentList);
Map map = new HashMap();
map.put("contextObjectStudentClass", class1);
System.out.println(MVEL.eval(s, map));
}
}
例外
Exception in thread "main" java.lang.RuntimeException: cannot invoke getter: getChild (see trace)
at org.mvel2.optimizers.impl.refl.nodes.GetterAccessor.getValue(GetterAccessor.java:70)
at org.mvel2.optimizers.impl.refl.nodes.VariableAccessor.getValue(VariableAccessor.java:37)
at org.mvel2.optimizers.dynamic.DynamicGetAccessor.getValue(DynamicGetAccessor.java:73)
at org.mvel2.ast.ASTNode.getReducedValueAccelerated(ASTNode.java:108)
at org.mvel2.ast.BinaryOperation.getReducedValueAccelerated(BinaryOperation.java:114)
at org.mvel2.compiler.ExecutableAccessor.getValue(ExecutableAccessor.java:38)
at org.mvel2.ast.IfNode.getReducedValueAccelerated(IfNode.java:73)
at org.mvel2.compiler.ExecutableAccessor.getValue(ExecutableAccessor.java:38)
at org.mvel2.ast.ForEachNode.getReducedValue(ForEachNode.java:136)
at org.mvel2.MVELInterpretedRuntime.parseAndExecuteInterpreted(MVELInterpretedRuntime.java:106)
at org.mvel2.MVELInterpretedRuntime.parse(MVELInterpretedRuntime.java:49)
at org.mvel2.MVEL.eval(MVEL.java:408)
at org.mvel2.ast.IfNode.getReducedValue(IfNode.java:89)
at org.mvel2.MVELInterpretedRuntime.parseAndExecuteInterpreted(MVELInterpretedRuntime.java:106)
at org.mvel2.MVELInterpretedRuntime.parse(MVELInterpretedRuntime.java:49)
at org.mvel2.MVEL.eval(MVEL.java:165)
at com.nucleus.rules.service.MvelTest.main(MvelTest.java:34)
Caused by: java.lang.NullPointerException
at org.mvel2.optimizers.impl.refl.nodes.NullSafe$1.getValue(NullSafe.java:39)
at org.mvel2.optimizers.impl.refl.nodes.NullSafe.getValue(NullSafe.java:54)
at org.mvel2.optimizers.impl.refl.nodes.GetterAccessor.getValue(GetterAccessor.java:40)
... 16 more