How to list all properties exposed by a Java class

Given a single Java class I'd like to be able to list all properties that are exposed in all ancestors and recursively traverse all their exposed properties (i.e. public or with getters/setters) in the same way.

Easier to explain with a simple example:

public class BaseClass1 {
    private int intProperty; // has getter and setter (not shown)
}
public class SubClass1 extends BaseClass1 {
    private int privateSoNotListed;
    public SubClass2 subClass2Property;
}
public class BaseClass2 {
    public String stringProperty;
}
public class SubClass2 extends BaseClass2 {
    private long longProperty; // has getter and setter (not shown)
}

Given SubClass1 above as input, the output would be something like this:

intProperty                      - int    [from BaseClass1]
subClass2Property.stringProperty - String [from BaseClass2]
subClass2Property.longProperty   - long   [from SubClass2]

It should be possible to write something like this using a bit of clever reflection but I'd rather not reinvent the wheel - is there an existing tool that can do this (perhaps an Eclipse plugin?)

EDIT: Eclipse's Type Hierarchy does a nice job of displaying properties for a single class - the ideal solution in my mind would be if this were a tree view (similar to Package Explorer) with the ability to expand properties that are themselves classes.

回答1:

See also the duplicate Recursive BeanUtils.describe(), which works also recursively. The following is a custom version we are using (logs in a log4j logger):

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

import org.apache.commons.beanutils.BeanUtilsBean;
import org.apache.commons.beanutils.ConvertUtilsBean;
import org.apache.log4j.Logger;

/*
 * See the original version: https://stackoverflow.com/questions/6133660/recursive-beanutils-describe
 */
public class Inspector  {

    public static void recursivelyDescribeAndLog(Object ob, Logger log){
        log.info(ob.getClass());
        try {
            Map<String, String> props = recursiveDescribe(ob);
            for (Map.Entry<String, String> p : props.entrySet()) {
                log.info(" -> " + p.getKey() + "="+p.getValue());
            }

        } catch (Throwable e) {
            log.error(e.getMessage(), e);
        }
    }

    public static Map<String, String> recursiveDescribe(Object object) {
        Set cache = new HashSet();
        return recursiveDescribe(object, null, cache);
    }

    private static Map<String, String> recursiveDescribe(Object object, String prefix, Set cache) {
        if (object == null || cache.contains(object)) return Collections.EMPTY_MAP;
        cache.add(object);
        prefix = (prefix != null) ? prefix + "." : "";

        Map<String, String> beanMap = new TreeMap<String, String>();

        Map<String, Object> properties = getProperties(object);
        for (String property : properties.keySet()) {
            Object value = properties.get(property);
            try {
                if (value == null) {
                    //ignore nulls
                } else if (Collection.class.isAssignableFrom(value.getClass())) {
                    beanMap.putAll(convertAll((Collection) value, prefix + property, cache));
                } else if (value.getClass().isArray()) {
                    beanMap.putAll(convertAll(Arrays.asList((Object[]) value), prefix + property, cache));
                } else if (Map.class.isAssignableFrom(value.getClass())) {
                    beanMap.putAll(convertMap((Map) value, prefix + property, cache));
                } else {
                    beanMap.putAll(convertObject(value, prefix + property, cache));
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return beanMap;
    }

    private static Map<String, Object> getProperties(Object object) {
        Map<String, Object> propertyMap = getFields(object);
        //getters take precedence in case of any name collisions
        propertyMap.putAll(getGetterMethods(object));
        return propertyMap;
    }

    private static Map<String, Object> getGetterMethods(Object object) {
        Map<String, Object> result = new HashMap<String, Object>();
        BeanInfo info;
        try {
            info = Introspector.getBeanInfo(object.getClass());
            for (PropertyDescriptor pd : info.getPropertyDescriptors()) {
                Method reader = pd.getReadMethod();
                if (reader != null) {
                    String name = pd.getName();
                    if (!"class".equals(name)) {
                        try {
                            Object value = reader.invoke(object);
                            result.put(name, value);
                        } catch (Exception e) {
                            //you can choose to do something here
                        }
                    }
                }
            }
        } catch (IntrospectionException e) {
            //you can choose to do something here
        } finally {
            return result;
        }

    }

    private static Map<String, Object> getFields(Object object) {
        return getFields(object, object.getClass());
    }

    private static Map<String, Object> getFields(Object object, Class<?> classType) {
        Map<String, Object> result = new HashMap<String, Object>();

        Class superClass = classType.getSuperclass();
        if (superClass != null) result.putAll(getFields(object, superClass));

        //get public fields only
        Field[] fields = classType.getFields();
        for (Field field : fields) {
            try {
                result.put(field.getName(), field.get(object));
            } catch (IllegalAccessException e) {
                //you can choose to do something here
            }
        }
        return result;
    }

    private static Map<String, String> convertAll(Collection<Object> values, String key, Set cache) {
        Map<String, String> valuesMap = new HashMap<String, String>();
        Object[] valArray = values.toArray();
        for (int i = 0; i < valArray.length; i++) {
            Object value = valArray[i];
            if (value != null) valuesMap.putAll(convertObject(value, key + "[" + i + "]", cache));
        }
        return valuesMap;
    }

    private static Map<String, String> convertMap(Map<Object, Object> values, String key, Set cache) {
        Map<String, String> valuesMap = new HashMap<String, String>();
        for (Object thisKey : values.keySet()) {
            Object value = values.get(thisKey);
            if (value != null) valuesMap.putAll(convertObject(value, key + "[" + thisKey + "]", cache));
        }
        return valuesMap;
    }

    private static ConvertUtilsBean converter = BeanUtilsBean.getInstance().getConvertUtils();

    private static Map<String, String> convertObject(Object value, String key, Set cache) {
        //if this type has a registered converted, then get the string and return
        if (converter.lookup(value.getClass()) != null) {
            String stringValue = converter.convert(value);
            Map<String, String> valueMap = new HashMap<String, String>();
            valueMap.put(key, stringValue);
            return valueMap;
        } else {
            //otherwise, treat it as a nested bean that needs to be described itself
            return recursiveDescribe(value, key, cache);
        }
    }
}

回答2:

have a look at apache commons beanutils. they have utility classes that will allow you to list properties (among other things) - specifically PropertyUtilsBean.getPropertyDescriptors().

note that their definiteion of a "property" is something that is accessible/editable via getter/setter methods. if you want to list fields you'd need to do something else

回答3:

Have just found a useful way of achieving something fairly similar to what was originally asked via Eclipse's Type Hierarchy.

There is a toggle named "Show All Inherited Members" as shown by the red arrow below:

After selecting this, the fields and methods from all superclasses are displayed in addition to those for the selected class (with a clear indication of where each one came from), as shown below:

(Of course, this includes more than just properties but since the getters are displayed in alphabetical order and there are icons for public/private/protected, it can be used to obtain this information easily enough.)