16

在我的应用程序中，我遇到了一个问题，即当类中的 getter 仅在接口中默认（Java 8 特性）时，结果没有 Java Beans 属性。即对于普通方法调用，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，是否还有其他解决方法，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”，因为你打错了喷嚏，所以它们往往会被破坏。

4

3 回答 3

3

这似乎确实是 Beans 中的错误遗漏Introspector。除了不使用方法之外，这是一种解决default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
于 2015-07-29T15:36:48.890 回答
1

我不知道我的回答是否会有所帮助，但我通过使用BeanUtils.getPropertyDescriptors(clazz)Spring 解决了类似的问题。它理解默认方法。

于 2017-10-13T13:46:43.247 回答
0

快速解决方法：

try {
    return PropertyUtils.getProperty(bean, property);
}
catch (NoSuchMethodException e) {
    String getMethod = "get" + property.substring(0, 1).toUpperCase() + property.substring(1);
    return MethodUtils.invokeMethod(bean, getMethod, new Object[]{});
}
于 2016-01-28T14:31:08.910 回答