java 从 POJO 生成 Map<String,String>

Generate Map<String,String> from POJO

提问by Andrew Toulouse

I have a POJO, and a (currently not-yet-built) class that will return Lists of it. I'd like to automatically generate the code necessary for the POJO to be accessed as a Map. Is this a good idea, is it possible to do automatically, and do I need to do this manually for every POJO I want to treat this way?

我有一个 POJO 和一个（目前尚未构建的）类，它将返回它的列表。我想自动生成作为 Map 访问的 POJO 所需的代码。这是一个好主意，是否可以自动执行，我是否需要为我想以这种方式处理的每个 POJO 手动执行此操作？

Thanks, Andy

谢谢，安迪

回答by BalusC

You can use Commons BeanUtilsBeanMapfor this.

您可以为此使用Commons BeanUtilsBeanMap。

Map map = new BeanMap(someBean);

---

---

Update: since that's not an option due to some apparent library dependency problems in Android, here's a basic kickoff example how you could do it with little help of Reflection API:

更新：由于 Android 中存在一些明显的库依赖问题，这不是一个选项，这里有一个基本的启动示例，您如何在几乎没有Reflection API帮助的情况下完成它：

public static Map<String, Object> mapProperties(Object bean) throws Exception {
    Map<String, Object> properties = new HashMap<>();
    for (Method method : bean.getClass().getDeclaredMethods()) {
        if (Modifier.isPublic(method.getModifiers())
            && method.getParameterTypes().length == 0
            && method.getReturnType() != void.class
            && method.getName().matches("^(get|is).+")
        ) {
            String name = method.getName().replaceAll("^(get|is)", "");
            name = Character.toLowerCase(name.charAt(0)) + (name.length() > 1 ? name.substring(1) : "");
            Object value = method.invoke(bean);
            properties.put(name, value);
        }
    }
    return properties;
}

If java.beansAPI were available, then you could just do:

如果java.beansAPI 可用，那么您可以这样做：

public static Map<String, Object> mapProperties(Object bean) throws Exception {
    Map<String, Object> properties = new HashMap<>();
    for (PropertyDescriptor property : Introspector.getBeanInfo(bean.getClass()).getPropertyDescriptors()) {
        String name = property.getName();
        Object value = property.getReadMethod().invoke(bean);
        properties.put(name, value);
    }
    return properties;
}

回答by mikeslattery

Here's my own implementation without any dependencies. Rather than make a copy of the object's state, it implements a live Map over the pojo. Android doesn't supportjava.beans, but you can use openbeansinstead.

这是我自己的实现，没有任何依赖项。它不是复制对象的状态，而是在 pojo 上实现一个实时 Map。Android不支持java.beans，但您可以改用openbeans。

import java.beans.*;  // Or, import com.googlecode.openbeans.*
import java.util.*;

public class BeanMap extends AbstractMap<String, Object> {
    private static final Object[] NO_ARGS = new Object[] {};
    private HashMap<String, PropertyDescriptor> properties;
    private Object bean;

    public BeanMap(Object bean) throws IntrospectionException {
        this.bean = bean;
        properties = new HashMap<String, PropertyDescriptor>();
        BeanInfo info = Introspector.getBeanInfo(bean.getClass());
        for(PropertyDescriptor property : info.getPropertyDescriptors()) {
            properties.put(property.getName(), property);
        }
    }

    @Override public Object get(Object key) {
        PropertyDescriptor property = properties.get(key);
        if(property == null)
            return null;
        try {
            return property.getReadMethod().invoke(bean, NO_ARGS);
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    @Override public Object put(String key, Object value) {
        PropertyDescriptor property = properties.get(key);
        try {
            return property.getWriteMethod().invoke(bean, new Object[] {value});
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    @Override public Set<Map.Entry<String, Object>> entrySet() {
        HashSet<Map.Entry<String, Object>> result = new HashSet<Map.Entry<String, Object>>(properties.size() * 2);
        for(PropertyDescriptor property : properties.values()) {
            String key = property.getName();
            Object value;
            try {
                value = property.getReadMethod().invoke(bean, NO_ARGS);
            } catch (Exception e) {
                throw new RuntimeException(e);
            }
            result.add(new PropertyEntry(key, value));
        }
        return Collections.unmodifiableSet(result);
    }

    @Override public int size() { return properties.size(); }

    @Override public boolean containsKey(Object key) { 
        return properties.containsKey(key);
    }

    class PropertyEntry extends AbstractMap.SimpleEntry<String, Object> {
        PropertyEntry(String key, Object value) {
            super(key, value);
        }

        @Override public Object setValue(Object value) {
            super.setValue(value);
            return BeanMap.this.put(getKey(), value);
        }
    }
}