Generate Map<String,String> from POJO
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 开发者_JAVA技巧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?
Thanks, Andy
You can use Commons BeanUtils BeanMap
for this.
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:
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.beans
API were available, then you could just do:
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;
}
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 support java.beans, but you can use openbeans instead.
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);
}
}
}
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