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

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<String,Object> 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.

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

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.

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<Object, Object> map = properties;

if you want some suffix, then just do

SerializationConfig config = mapper.getSerializationConfig()
                .withRootName("suffix");
mapper.setConfig(config);

need to add this dependency

<dependency>
  <groupId>com.fasterxml.jackson.dataformat</groupId>
  <artifactId>jackson-dataformat-properties</artifactId>
</dependency>

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.

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

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.

The best solution is to use Dozer. You just need something like this in the mapper file:

<mapping map-id="myTestMapping">
  <class-a>org.dozer.vo.map.SomeComplexType</class-a>
  <class-b>java.util.Map</class-b>
</mapping> 

And that's it, Dozer takes care of the rest!!!

Dozer Documentation URL

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)

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!

By using Gson,

1. Convert POJO object to Json

2. Convert Json to Map

       retMap = new Gson().fromJson(new Gson().toJson(object), 
               new TypeToken<HashMap<String, Object>>() {}.getType()
       );
   

We can use the Jackson library to convert a Java object into a Map easily.

<dependency>
   <groupId>com.fasterxml.jackson.core</groupId>
   <artifactId>jackson-databind</artifactId>
   <version>2.6.3</version>
</dependency>

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<String> 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 -> Map
    Map<String, Object> map = objectMapper.convertValue(emp, 
    Map.class);
    System.out.println(map);

 }

}

Output:

{name=XYZ, id=1011, skills=[python, java]}