Best way of invoking getter by reflection

Question

I need to get the value of a field with a specific annotation  So with reflection I am able to get this Field Object  The problem is that this field will be always private though I know in advance it will always have a getter method  I know that I can use setAccesible true  and get its value  when there is no PermissionManager   though I prefer to invoke its getter method   I know that I could look for the method by looking for  get fieldName   though I know for example for boolean fields are sometimes named as  is fieldName     I wonder if there is a better way to invoke this getter  many frameworks use getters setters to access the attributes so maybe they do in another way    Thanks

User · Answer

The naming convention is part of the well-established JavaBeans specification and is supported by the classes in the java beans package

User · Answer

You can use Reflections framework for this  import static org reflections ReflectionUtils    Set lt Method gt  getters   ReflectionUtils getAllMethods someClass        withModifier Modifier PUBLIC   withPrefix  get    withAnnotation annotation

User · Answer

I think this should point you towards the right direction   import java beans    for  PropertyDescriptor pd   Introspector getBeanInfo Foo class  getPropertyDescriptors        if  pd getReadMethod      null  amp  amp    class  equals pd getName         System out println pd getReadMethod   invoke foo        Note that you could create BeanInfo or PropertyDescriptor instances yourself  i e  without using Introspector  However  Introspector does some caching internally which is normally a Good Thing  tm   If you re happy without a cache  you can even go for     TODO check for non-existing readMethod Object value   new PropertyDescriptor  name   Person class  getReadMethod   invoke person     However  there are a lot of libraries that extend and simplify the java beans API  Commons BeanUtils is a well known example  There  you d simply do   Object value   PropertyUtils getProperty person   name      BeanUtils comes with other handy stuff  i e  on-the-fly value conversion  object to string  string to object  to simplify setting properties from user input

User · Answer

You can invoke reflections and also  set order of sequence for getter for values through annotations  public class Student        private String grade       private String name       private String id       private String gender       private Method   methods        Retention RetentionPolicy RUNTIME      public  interface Order           int value                          Sort methods as per Order Annotations                 return             private void sortMethods              methods   Student class getMethods             Arrays sort methods  new Comparator lt Method gt                  public int compare Method o1  Method o2                    Order or1   o1 getAnnotation Order class                   Order or2   o2 getAnnotation Order class                   if  or1    null  amp  amp  or2    null                        return or1 value   - or2 value                                      else if  or1    null  amp  amp  or2    null                        return -1                                    else if  or1    null  amp  amp  or2    null                        return 1                                    return o1 getName   compareTo o2 getName                                                     Read Elements                 return             public void readElements             int pos   0                         Sort Methods                     if  methods    null                sortMethods                      for  Method method   methods                String name   method getName                if  name startsWith  get    amp  amp   name equalsIgnoreCase  getClass                      pos                    String value                       try                       value    String  method invoke this                                     catch  IllegalAccessException   IllegalArgumentException   InvocationTargetException e                        e printStackTrace                                      System out println name     Pos      pos     Value      value                                                                 Getter and Setter Methods                  param grade         param name         param id         param gender             public Student String grade  String name  String id  String gender            super            this grade   grade          this name   name          this id   id          this gender   gender                         return the grade              Order value   4      public String getGrade             return grade                         param grade the grade to set             public void setGrade String grade            this grade   grade                         return the name              Order value   2      public String getName             return name                         param name the name to set             public void setName String name            this name   name                         return the id              Order value   1      public String getId             return id                         param id the id to set             public void setId String id            this id   id                         return the gender              Order value   3      public String getGender             return gender                         param gender the gender to set             public void setGender String gender            this gender   gender                        Main                 param args         throws IOException         throws SQLException         throws InvocationTargetException         throws IllegalArgumentException         throws IllegalAccessException             public static void main String args    throws IOException  SQLException  IllegalAccessException              IllegalArgumentException  InvocationTargetException           Student student   new Student  A    Anand    001    Male            student readElements                Output when sorted  getId Pos  1 Value  001 getName Pos  2 Value  Anand getGender Pos  3 Value  Male getGrade Pos  4 Value  A

[java] Best way of invoking getter by reflection

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