How to convert a Java object bean to key-value pairs and vice versa

Question

Say I have a very simple java object that only has some getXXX and setXXX properties   This object is used only to handle values  basically a record or a type-safe  and performant  map   I often need to covert this object to key value pairs  either strings or type safe  or convert from key value pairs to this object   Other than reflection or manually writing code to do this conversion  what is the best way to achieve this   An example might be sending this object over jms  without using the ObjectMessage type  or converting an incoming message to the right kind of object

User · Answer

You should write a generic transformation Service! Use generics to keep it type free (so you can convert every object to key=>value and back).

What field should be the key? Get that field from the bean and append any other non transient value in a value map.

The way back is pretty easy. Read key(x) and write at first the key and then every list entry back to a new object.

You can get the property names of a bean with the apache commons beanutils!

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The best solution is to use Dozer  You just need something like this in the mapper file    lt mapping map-id  myTestMapping  gt     lt class-a gt org dozer vo map SomeComplexType lt  class-a gt     lt class-b gt java util Map lt  class-b gt   lt  mapping gt     And that s it  Dozer takes care of the rest     Dozer Documentation URL

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Code generation would be the only other way I can think of  Personally  I d got with a generally reusable reflection solution  unless that part of the code is absolutely performance-critical   Using JMS sounds like overkill  additional dependency  and that s not even what it s meant for   Besides  it probably uses reflection as well under the hood

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We can use the Jackson library to convert a Java object into a Map easily    lt dependency gt      lt groupId gt com fasterxml jackson core lt  groupId gt      lt artifactId gt jackson-databind lt  artifactId gt      lt version gt 2 6 3 lt  version gt   lt  dependency gt    If using in an Android project  you can add jackson in your app s build gradle as follows   implementation  com fasterxml jackson core jackson-core 2 9 8  implementation  com fasterxml jackson core jackson-annotations 2 9 8  implementation  com fasterxml jackson core jackson-databind 2 9 8    Sample Implementation  public class Employee        private String name      private int id      private List lt String gt  skillSet          getters setters    public class ObjectToMap     public static void main String   args         ObjectMapper objectMapper   new ObjectMapper         Employee emp   new Employee        emp setName  XYZ        emp setId 1011       emp setSkillSet Arrays asList  python   java             object - gt  Map     Map lt String  Object gt  map   objectMapper convertValue emp       Map class       System out println map            Output    name XYZ  id 1011  skills  python  java

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One other possible way is here   The BeanWrapper offers functionality to set and get property values  individually  or in bulk   get property descriptors  and to query properties to determine if they  are readable or writable   Company c   new Company     BeanWrapper bwComp   BeanWrapperImpl c    bwComp setPropertyValue  name    your Company

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Use juffrou-reflect s BeanWrapper  It is very performant  Here is how you can transform a bean into a map  public static Map lt String  Object gt  getBeanMap Object bean        Map lt String  Object gt  beanMap   new HashMap lt String  Object gt         BeanWrapper beanWrapper   new BeanWrapper BeanWrapperContext create bean getClass          for String propertyName   beanWrapper getPropertyNames            beanMap put propertyName  beanWrapper getValue propertyName        return beanMap     I developed Juffrou myself  It s open source  so you are free to use it and modify  And if you have any questions regarding it  I ll be more than happy to respond  Cheers Carlos

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JSON  for example using XStream   Jettison  is a simple text format with key value pairs  It is supported for example by the Apache ActiveMQ JMS message broker for Java object exchange with other platforms   languages

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My JavaDude Bean Annotation Processor generates code to do this    http   javadude googlecode com  For example    Bean    createPropertyMap true    properties        Property name  name         Property name  phone   bound true        Property name  friend   type Person class  kind PropertyKind LIST        public class Person extends PersonGen      The above generates superclass PersonGen that includes a createPropertyMap   method that generates a Map for all properties defined using  Bean    Note that I m changing the API slightly for the next version -- the annotation attribute will be defineCreatePropertyMap true

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If it comes to a simple object tree to key value list mapping  where key might be a dotted path description from the object s root element to the leaf being inspected  it s rather obvious that a tree conversion to a key-value list is comparable to an object to xml mapping  Each element within an XML document has a defined position and can be converted into a path  Therefore I took XStream as a basic and stable conversion tool and replaced the hierarchical driver and writer parts with an own implementation  XStream also comes with a basic path tracking mechanism which - being combined with the other two - strictly leads to a solution being suitable for the task

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Lots of potential solutions  but let s add just one more  Use Jackson  JSON processing lib  to do  json-less  conversion  like   ObjectMapper m   new ObjectMapper    Map lt String Object gt  props   m convertValue myBean  Map class   MyBean anotherBean   m convertValue props  MyBean class      this blog entry has some more examples   You can basically convert any compatible types  compatible meaning that if you did convert from type to JSON  and from that JSON to result type  entries would match  if configured properly can also just ignore unrecognized ones    Works well for cases one would expect  including Maps  Lists  arrays  primitives  bean-like POJOs

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If you really really want performance you can go the code generation route   You can do this on your on by doing your own reflection and building a mixin AspectJ ITD   Or you can use Spring Roo and make a Spring Roo Addon  Your Roo addon will do something similar to the above but will be available to everyone who uses Spring Roo and you don t have to use Runtime Annotations   I have done both  People crap on Spring Roo but it really is the most comprehensive code generation for Java

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With the help of Jackson library  I was able to find all class properties of type String integer double  and respective values in a Map class   without using reflections api    TestClass testObject   new TestClass    com fasterxml jackson databind ObjectMapper m   new com fasterxml jackson databind ObjectMapper     Map lt String Object gt  props   m convertValue testObject  Map class    for Map Entry lt String  Object gt  entry   props entrySet         if entry getValue   instanceof String    entry getValue   instanceof Integer    entry getValue   instanceof Double           System out println entry getKey      -- gt     entry getValue

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Probably late to the party  You can use Jackson and convert it into a Properties object  This is suited for Nested classes and if you want the key in the for a b c value   JavaPropsMapper mapper   new JavaPropsMapper    Properties properties   mapper writeValueAsProperties sct   Map lt Object  Object gt  map   properties    if you want some suffix  then just do  SerializationConfig config   mapper getSerializationConfig                    withRootName  suffix    mapper setConfig config     need to add this dependency   lt dependency gt     lt groupId gt com fasterxml jackson dataformat lt  groupId gt     lt artifactId gt jackson-dataformat-properties lt  artifactId gt   lt  dependency gt

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If you do not want to hardcode calls to each getter and setter  reflection is the only way to call these methods  but it is not hard    Can you refactor the class in question to use a Properties object to hold the actual data  and let each getter and setter just call get set on it   Then you have a structure well suited for what you want to do   There is even methods to save and load them in the key-value form

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There is of course the absolute simplest means of conversion possible - no conversion at all    instead of using private variables defined in the class  make the class contain only a HashMap  which stores the values for the instance   Then your getters and setters return and set values into and out of the HashMap  and when it is time to convert it to a map  voila  - it is already a map   With a little bit of AOP wizardry  you could even maintain the inflexibility inherent in a bean by allowing you to still use getters and setters specific to each values name  without having to actually write the individual getters and setters

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There is always apache commons beanutils but of course it uses reflection under the hood

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You could use the Joda framework   http   joda sourceforge net   and take advantage of JodaProperties   This does stipulate that you create beans in a particular way however  and implement a specific interface   It does then however  allow you to return a property map from a specific class  without reflection   Sample code is here   http   pbin oogly co uk listings viewlistingdetail 0e78eb6c76d071b4e22bbcac748c57

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You can use the java 8 stream filter collector properties   public Map lt String  Object gt  objectToMap Object obj        return Arrays stream YourBean class getDeclaredMethods                 filter p - gt   p getName   startsWith  set                 filter p - gt   p getName   startsWith  getClass                 filter p - gt   p getName   startsWith  setClass                 collect Collectors toMap                      d - gt  d getName   substring 3                       m - gt                            try                               Object result   m invoke obj                               return result                            catch  Exception e                                return                                                       p1  p2  - gt  p1

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By using Gson    Convert POJO object to Json Convert Json to Map      retMap   new Gson   fromJson new Gson   toJson object                new TypeToken lt HashMap lt String  Object gt  gt       getType

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This is a method for converting a Java object to a Map  public static Map lt String  Object gt  ConvertObjectToMap Object obj  throws      IllegalAccessException       IllegalArgumentException       InvocationTargetException           Class lt   gt  pomclass   obj getClass            pomclass   obj getClass            Method   methods   obj getClass   getMethods              Map lt String  Object gt  map   new HashMap lt String  Object gt             for  Method m   methods               if  m getName   startsWith  get    amp  amp   m getName   startsWith  getClass                    Object value    Object  m invoke obj                 map put m getName   substring 3    Object  value                              return map      This is how to call it     Test test   new Test      Map lt String  Object gt  map   ConvertObjectToMap test

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With Java 8 you may try this    public Map lt String  Object gt  toKeyValuePairs Object instance        return Arrays stream Bean class getDeclaredMethods                 collect Collectors toMap                      Method  getName                      m - gt                            try                               Object result   m invoke instance                               return result    null   result                                 catch  Exception e                                return

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When using Spring  one can also use Spring Integration object-to-map-transformer  It s probably not worth adding Spring as a dependency just for this   For documentation  search for  Object-to-Map Transformer  on http   docs spring io spring-integration docs 4 0 4 RELEASE reference html messaging-transformation-chapter html  Essentially  it traverses the entire object graph reachable from the object given as input  and produces a map from all primitive type String fields on the objects  It can be configured to output either    a flat map   rootObject someField Joe  rootObject leafObject someField Jane   or a structured map   someField Joe  leafObject  someField Jane      Here s an example from their page   public class Parent      private Child child      private String name          setters and getters are omitted    public class Child     private String name      private List lt String gt  nickNames        setters and getters are omitted     Output will be         person name George  person child name Jenna    person child nickNames 0  Bimbo       etc    A reverse transformer is also available

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Simply using reflection and Groovy    def Map toMap object                 return object  properties findAll   it key     class     collectEntries               it value    null    it value instanceof Serializable    it key  it value     it key    toMap it value               def toObject map  obj                map each           def field   obj class getDeclaredField it key          if  it value    null                if  field getType   equals it value class                    obj   it key    it value              else if  it value instanceof Map                   def objectFieldValue   obj   it key                  def fieldValue    objectFieldValue    null    field getType   newInstance     objectFieldValue                 obj   it key    toObject it value fieldValue                                     return obj

[java] How to convert a Java object (bean) to key-value pairs (and vice versa)?

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