Java Reflection: How can I get the all getter methods of a java class and invoke them

Question

I write a java class which has many getters..now I want to get all getter methods and invoke them sometime..I know there are methods such as getMethods() or getMethod(String name, Class... parameterTypes) ,but i just want to get the getter indeed..., use regex? anyone can tell me ?Thanks!

Answer 1

Don't use regex, use the Introspector:

for(PropertyDescriptor propertyDescriptor :      Introspector.getBeanInfo(yourClass).getPropertyDescriptors()){      // propertyEditor.getReadMethod() exposes the getter     // btw, this may be null if you have a write-only property     System.out.println(propertyDescriptor.getReadMethod()); } 

Usually you don't want properties from Object.class, so you'd use the method with two parameters:

Introspector.getBeanInfo(yourClass, stopClass) // usually with Object.class as 2nd param // the first class is inclusive, the second exclusive 

BTW: there are frameworks that do that for you and present you a high-level view. E.g. commons/beanutils has the method

Map<String, String> properties = BeanUtils.describe(yourObject); 

(docs here) which does just that: find and execute all the getters and store the result in a map. Unfortunately, BeanUtils.describe() converts all the property values to Strings before returning. WTF. Thanks @danw

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Update:

Here's a Java 8 method that returns a Map<String, Object> based on an object's bean properties.

public static Map<String, Object> beanProperties(Object bean) {   try {     return Arrays.asList(          Introspector.getBeanInfo(bean.getClass(), Object.class)                      .getPropertyDescriptors()       )       .stream()       // filter out properties with setters only       .filter(pd -> Objects.nonNull(pd.getReadMethod()))       .collect(Collectors.toMap(         // bean property name         PropertyDescriptor::getName,         pd -> { // invoke method to get value             try {                  return pd.getReadMethod().invoke(bean);             } catch (Exception e) {                 // replace this with better error handling                return null;             }         }));   } catch (IntrospectionException e) {     // and this, too     return Collections.emptyMap();   } } 

You probably want to make error handling more robust, though. Sorry for the boilerplate, checked exceptions prevent us from going fully functional here.

---

Turns out that Collectors.toMap() hates null values. Here's a more imperative version of the above code:

public static Map<String, Object> beanProperties(Object bean) {     try {         Map<String, Object> map = new HashMap<>();         Arrays.asList(Introspector.getBeanInfo(bean.getClass(), Object.class)                                   .getPropertyDescriptors())               .stream()               // filter out properties with setters only               .filter(pd -> Objects.nonNull(pd.getReadMethod()))               .forEach(pd -> { // invoke method to get value                   try {                       Object value = pd.getReadMethod().invoke(bean);                       if (value != null) {                           map.put(pd.getName(), value);                       }                   } catch (Exception e) {                       // add proper error handling here                   }               });         return map;     } catch (IntrospectionException e) {         // and here, too         return Collections.emptyMap();     } } 

Here's the same functionality in a more concise way, using JavaSlang:

public static Map<String, Object> javaSlangBeanProperties(Object bean) {     try {         return Stream.of(Introspector.getBeanInfo(bean.getClass(), Object.class)                                      .getPropertyDescriptors())                      .filter(pd -> pd.getReadMethod() != null)                      .toJavaMap(pd -> {                          try {                              return new Tuple2<>(                                      pd.getName(),                                      pd.getReadMethod().invoke(bean));                          } catch (Exception e) {                              throw new IllegalStateException();                          }                      });     } catch (IntrospectionException e) {         throw new IllegalStateException();      } } 

And here's a Guava version:

public static Map<String, Object> guavaBeanProperties(Object bean) {     Object NULL = new Object();     try {         return Maps.transformValues(                 Arrays.stream(                         Introspector.getBeanInfo(bean.getClass(), Object.class)                                     .getPropertyDescriptors())                       .filter(pd -> Objects.nonNull(pd.getReadMethod()))                       .collect(ImmutableMap::<String, Object>builder,                                (builder, pd) -> {                                    try {                                        Object result = pd.getReadMethod()                                                          .invoke(bean);                                        builder.put(pd.getName(),                                                    firstNonNull(result, NULL));                                    } catch (Exception e) {                                        throw propagate(e);                                    }                                },                                (left, right) -> left.putAll(right.build()))                       .build(), v -> v == NULL ? null : v);     } catch (IntrospectionException e) {         throw propagate(e);     } } 

Answer 2

You can use Reflections framework for this

import org.reflections.ReflectionUtils.*; Set<Method> getters = ReflectionUtils.getAllMethods(someClass,       ReflectionUtils.withModifier(Modifier.PUBLIC), ReflectionUtils.withPrefix("get"));