在我的应用程序中,我遇到了一个问题,即当类中的 getter 仅在接口(interface)中默认设置时(Java 8 功能),结果没有 Java Beans 属性。 IE。对于普通方法调用,它就像标准方法一样工作,但对于通过“属性”访问,它突然表现不同......
这是一个测试用例:
import java.beans.Introspector;
import java.util.Arrays;
import java.util.stream.Collectors;
import org.apache.commons.beanutils.PropertyUtils;
public class test
{
public static void main (String[] arguments) throws Exception
{
// Normal language-level invocation, works fine.
System.out.println (new Bean1 ().getFoo ());
System.out.println (new Bean2 ().getFoo ());
// Printing Java Beans properties; Bean2 doesn't have 'foo' property...
System.out.println (Arrays.stream (Introspector.getBeanInfo (Bean1.class).getPropertyDescriptors ())
.map ((property) -> property.getName ())
.collect (Collectors.joining (", ")));
System.out.println (Arrays.stream (Introspector.getBeanInfo (Bean2.class).getPropertyDescriptors ())
.map ((property) -> property.getName ())
.collect (Collectors.joining (", ")));
// First call behaves as expected, second dies with exception.
System.out.println (PropertyUtils.getProperty (new Bean1 (), "foo"));
System.out.println (PropertyUtils.getProperty (new Bean2 (), "foo"));
}
public interface Foo
{
default String getFoo ()
{
return "default foo";
}
}
public static class Bean1 implements Foo
{
@Override
public String getFoo ()
{
return "special foo";
}
}
public static class Bean2 implements Foo
{ }
}
结果:
special foo
default foo
class, foo
class
special foo
Exception in thread "main" java.lang.NoSuchMethodException: Unknown property 'foo' on class 'class test$Bean2'
at org.apache.commons.beanutils.PropertyUtilsBean.getSimpleProperty(PropertyUtilsBean.java:1257)
at org.apache.commons.beanutils.PropertyUtilsBean.getNestedProperty(PropertyUtilsBean.java:808)
at org.apache.commons.beanutils.PropertyUtilsBean.getProperty(PropertyUtilsBean.java:884)
at org.apache.commons.beanutils.PropertyUtils.getProperty(PropertyUtils.java:464)
at test.main(test.java:21)
问题:我做错了什么还是 Java 中的错误?除了从不使用默认方法(对于 getter/setter)之外,是否有其他解决方法,以防您以后可能需要将它们作为“属性”访问?
我一直讨厌 Java“约定俗成的属性”,因为打喷嚏的方式不对而容易出错。
最佳答案
这似乎确实是 Beans Introspector
中的一个错误遗漏。除了不使用 default
方法之外,还有一个解决方法:
public static void main (String[] arguments) throws Exception {
testBean(new Bean1());
System.out.println();
testBean(new Bean2());
}
static void testBean(Object bean) throws Exception {
PropertyDescriptor[] pd
= Introspector.getBeanInfo(bean.getClass()).getPropertyDescriptors();
System.out.println(Arrays.stream(pd)
.map(PropertyDescriptor::getName).collect(Collectors.joining(", ")));
for(PropertyDescriptor p: pd)
System.out.println(p.getDisplayName()+": "+p.getReadMethod().invoke(bean));
}
public interface Foo {
default String getFoo() {
return "default foo";
}
}
public static class Bean1 implements Foo {
@Override
public String getFoo() {
return "special foo";
}
}
public static class Bean2BeanInfo extends SimpleBeanInfo {
private final BeanInfo ifBeanInfo;
public Bean2BeanInfo() throws IntrospectionException {
ifBeanInfo=Introspector.getBeanInfo(Foo.class);
}
@Override
public BeanInfo[] getAdditionalBeanInfo() {
return new BeanInfo[]{ifBeanInfo};
}
}
public static class Bean2 implements Foo { }
class, foo
class: class helper.PropTest$Bean1
foo: special foo
class, foo
class: class helper.PropTest$Bean2
foo: default foo
关于Java 8 接口(interface)默认方法似乎没有声明属性,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/31703563/