Convert a Map<String, String> to a POJO
JsonDictionaryJacksonPojoJson Problem Overview
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
Json Solutions
Solution 1 - Json
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.
Solution 2 - Json
A solution with Gson:
Gson gson = new Gson();
JsonElement jsonElement = gson.toJsonTree(map);
MyPojo pojo = gson.fromJson(jsonElement, MyPojo.class);
Solution 3 - Json
if you have generic types in your class you should use TypeReference with convertValue().
final ObjectMapper mapper = new ObjectMapper();
final MyPojo<MyGenericType> pojo = mapper.convertValue(map, new TypeReference<MyPojo<MyGenericType>>() {});
Also you can use that to convert a pojo to java.util.Map back.
final ObjectMapper mapper = new ObjectMapper();
final Map<String, Object> map = mapper.convertValue(pojo, new TypeReference<Map<String, Object>>() {});
Solution 4 - Json
ObjectMapper objectMapper = new ObjectMapper();
//if all properties are not in class use this
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
final MyPojo pojo = objectMapper.convertValue(map, MyPojo.class);
same as first answer but i got an error using that because i dont want all property of the map converted to the calss. and i fount objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false); this as the solution
Solution 5 - Json
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<String, String> map = new HashMap<String, String>(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<String, Object> then you can copy over arbitrarily deep nested properties (with Map<String, String> you only get one level).
Solution 6 - Json
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<String, Object> map = new HashMap<>();
map.put("success", true);
map.put("data", "testString");
runBeanUtilsPopulate(map);
runJacksonMapper(map);
}
private static void runBeanUtilsPopulate(Map<String, Object> map) {
long t1 = System.currentTimeMillis();
for (int i = 0; i < 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<String, Object> map) {
long t1 = System.currentTimeMillis();
for (int i = 0; i < 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));
}}
Solution 7 - Json
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 <T> T convert(Map<String, Object> aMap, Class<T> 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;
}
Solution 8 - Json
> 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<String, String> info = new HashMap<>();
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)
*/
Solution 9 - Json
@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<String, Object> map = new HashMap<>();
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<String, Object> map) {
long t1 = System.currentTimeMillis();
for (int i = 0; i < 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<String, Object> map) {
long t1 = System.currentTimeMillis();
for (int i = 0; i < 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;
}
}