Convert a Map String String to a POJO

Question

I ve been looking at Jackson  but is seems I would have to convert the Map to JSON  and then the resulting JSON to the POJO    Is there a way to convert a Map directly to a POJO

User · Answer

A solution with Gson   Gson gson   new Gson    JsonElement jsonElement   gson toJsonTree map   MyPojo pojo   gson fromJson jsonElement  MyPojo class

User · Answer

Yes  its definitely possible to avoid the intermediate conversion to JSON  Using a deep-copy tool like Dozer you can convert the map directly to a POJO  Here is a simplistic example   Example POJO   public class MyPojo implements Serializable       private static final long serialVersionUID   1L       private String id      private String name      private Integer age      private Double savings       public MyPojo             super                  Getters setters       Override     public String toString             return String format                   MyPojo id    s  name    s  age    s  savings    s    getId                    getName    getAge    getSavings               Sample conversion code   public class CopyTest        Test     public void testCopyMapToPOJO   throws Exception           final Map lt String  String gt  map   new HashMap lt String  String gt  4           map put  id    5            map put  name    Bob            map put  age    23            map put  savings    2500 39            map put  extra    foo             final DozerBeanMapper mapper   new DozerBeanMapper            final MyPojo pojo   mapper map map  MyPojo class           System out println pojo             Output      MyPojo id   5  name   Bob  age   23  savings   2500 39    Note  If you change your source map to a Map lt String  Object gt  then you can copy over arbitrarily deep nested properties  with Map lt String  String gt  you only get one level

User · Answer

convert Map to POJO example Notice the Map key contains underline and field variable is hump     User class POJO  import com fasterxml jackson annotation JsonProperty  import lombok Data    Data public class User        JsonProperty  user name       private String userName       JsonProperty  pass word       private String passWord      The App class test the example  import java util HashMap  import java util Map   import com fasterxml jackson databind ObjectMapper   public class App       public static void main String   args            Map lt String  String gt  info   new HashMap lt  gt             info put  user name    Q10Viking            info put  pass word    123456             ObjectMapper mapper   new ObjectMapper            User user   mapper convertValue info  User class            System out println  -------------------------------            System out println user              output ------------------------------- User userName Q10Viking  passWord 123456

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I have tested both Jackson and BeanUtils and found out that BeanUtils is  much faster  In my machine Windows8 1   JDK1 7  I got this result   BeanUtils t2-t1   286 Jackson t2-t1   2203     public class MainMapToPOJO    public static final int LOOP MAX COUNT   1000   public static void main String   args        Map lt String  Object gt  map   new HashMap lt  gt         map put  success   true       map put  data    testString         runBeanUtilsPopulate map        runJacksonMapper map      private static void runBeanUtilsPopulate Map lt String  Object gt  map        long t1   System currentTimeMillis        for  int i   0  i  lt  LOOP MAX COUNT  i              try               TestClass bean   new TestClass                BeanUtils populate bean  map             catch  IllegalAccessException e                e printStackTrace              catch  InvocationTargetException e                e printStackTrace                        long t2   System currentTimeMillis        System out println  BeanUtils t2-t1       String valueOf t2 - t1       private static void runJacksonMapper Map lt String  Object gt  map        long t1   System currentTimeMillis        for  int i   0  i  lt  LOOP MAX COUNT  i              ObjectMapper mapper   new ObjectMapper            TestClass testClass   mapper convertValue map  TestClass class             long t2   System currentTimeMillis        System out println  Jackson t2-t1       String valueOf t2 - t1

User · Answer

The answers provided so far using Jackson are so good  but still you could have a util function to help you convert different POJOs as follows       public static  lt T gt  T convert Map lt String  Object gt  aMap  Class lt T gt  t            try               return objectMapper                      convertValue aMap  objectMapper getTypeFactory   constructType t              catch  Exception e                log error  converting failed  aMap      class       getJsonString aMap   t getClass   getSimpleName    e                     return null

User · Answer

Well  you can achieve that with Jackson  too   and it seems to be more comfortable since you were considering using jackson    Use ObjectMapper s convertValue method   final ObjectMapper mapper   new ObjectMapper       jackson s objectmapper final MyPojo pojo   mapper convertValue map  MyPojo class     No need to convert into JSON string or something else  direct conversion does much faster

User · Answer

Hamedz if use many data  use Jackson to convert light data  use apache     TestCase     import java lang reflect InvocationTargetException  import java util HashMap  import java util Map   import org apache commons beanutils BeanUtils   import com fasterxml jackson databind ObjectMapper   import lombok AllArgsConstructor  import lombok Data  import lombok NoArgsConstructor   public class TestPerf        public static final int LOOP MAX COUNT   1000       public static void main String   args            Map lt String  Object gt  map   new HashMap lt  gt             map put  success   true           map put  number   1000           map put  longer   1000L           map put  doubler   1000D           map put  data1    testString            map put  data2    testString            map put  data3    testString            map put  data4    testString            map put  data5    testString            map put  data6    testString            map put  data7    testString            map put  data8    testString            map put  data9    testString            map put  data10    testString             runBeanUtilsPopulate map            runJacksonMapper map              private static void runBeanUtilsPopulate Map lt String  Object gt  map            long t1   System currentTimeMillis            for  int i   0  i  lt  LOOP MAX COUNT  i                  try                   TestClass bean   new TestClass                    BeanUtils populate bean  map                 catch  IllegalAccessException e                    e printStackTrace                  catch  InvocationTargetException e                    e printStackTrace                                    long t2   System currentTimeMillis            System out println  BeanUtils t2-t1       String valueOf t2 - t1               private static void runJacksonMapper Map lt String  Object gt  map            long t1   System currentTimeMillis            for  int i   0  i  lt  LOOP MAX COUNT  i                  ObjectMapper mapper   new ObjectMapper                TestClass testClass   mapper convertValue map  TestClass class                     long t2   System currentTimeMillis            System out println  Jackson t2-t1       String valueOf t2 - t1                Data      AllArgsConstructor      NoArgsConstructor     public static class TestClass           private Boolean success          private Integer number          private Long longer          private Double doubler          private String data1          private String data2          private String data3          private String data4          private String data5          private String data6          private String data7          private String data8          private String data9          private String data10

User · Answer

if you have generic types in your class you should use TypeReference with convertValue     final ObjectMapper mapper   new ObjectMapper    final MyPojo lt MyGenericType gt  pojo   mapper convertValue map  new TypeReference lt MyPojo lt MyGenericType gt  gt           Also you can use that to convert a pojo to java util Map back   final ObjectMapper mapper   new ObjectMapper    final Map lt String  Object gt  map   mapper convertValue pojo  new TypeReference lt Map lt String  Object gt  gt

[json] Convert a Map<String, String> to a POJO

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