So, I am writing a "POJO to JSON" converter. I want to be able to pass a List<T> object and convert to JSON.
Hope this makes sense
public abstract class Jsonator<T> implements Serializable { private Class<T> entityClass; private JSONObject json; private JSONArray jsonArray; public Jsonator(Class<T> entityClass) { this.entityClass = entityClass; } public void convert(List<T> paObjectList) throws IllegalArgumentException, IllegalAccessException { json = new JSONObject(); jsonArray = new JSONArray(); try { for (Object obj : paObjectList) { JSONObject objJson = new JSONObject(); Class<?> kls = obj.getClass(); Field[] fields = kls.getFields(); for (Field field : fields) { objJson.put(field.getName(), (T) field.get(obj)); } jsonArray.add(objJson); } json.put("results", jsonArray); } catch (Exception ex) { } } public String error() { return "ERROR"; } public String results() { if (json != null) { return json.toJSONString(); } return "[]"; } }
When I go to the Object obj section, my obj correct. I can debug it and see the name and value of the class.
Let's say the class is this:
public class User { private firstName; private lastName; ... getters....setters....etc... }
So now obj is a website. So I'm trying to get the field names (firstName, lastName), but the field object is empty.
What am I doing wrong?
thanks
EDIT
I got it to work! This is not finished code, but it does exactly what I want now. I read that Google and Jackson will do it too. If someone can provide a good link on how to selectively select properties from POJO, then I'm all ears.
Or better yet, I would like to know WHY I should not do this?
Thanks!
Jsonator (NOT COMPLETED)
import java.io.Serializable; import java.lang.reflect.Field; import java.util.List; import org.json.simple.JSONArray; import org.json.simple.JSONObject; public abstract class Jsonator<T> implements Serializable { private Class<T> entityClass; private JSONObject json; private JSONArray jsonArray; public Jsonator(Class<T> entityClass) { this.entityClass = entityClass; } public void convert(List<T> paObjectList) throws IllegalArgumentException, IllegalAccessException { json = new JSONObject(); jsonArray = new JSONArray(); try { for (Object obj : paObjectList) { JSONObject objJson = new JSONObject(); Class<?> kls = obj.getClass(); Field[] fields = kls.getDeclaredFields(); for (Field field : fields) { field.setAccessible(true); objJson.put(field.getName(), field.get(obj)); } jsonArray.add(objJson); } json.put("results", jsonArray); } catch (SecurityException ex) { ex.printStackTrace(); } catch (Exception ex) { ex.printStackTrace(); } } public String error() { return "ERROR"; } public String results() { if (json != null) { return json.toJSONString(); } return "[]"; } }
Site class
import java.io.Serializable; import javax.persistence.Column; import javax.persistence.Entity; import javax.persistence.GeneratedValue; import javax.persistence.Id; import javax.persistence.Table; import org.hibernate.annotations.GenericGenerator; @Entity @Table(name = "Sites") public class Site implements Serializable { private String siteKey; private String site; private String siteType; private String address1; private String address2; private String city; private String zipCode; private String createdBy; private String glCode; public Site() { } @Id @GenericGenerator(name = "generator", strategy = "guid", parameters = {}) @GeneratedValue(generator = "generator") public String getSiteKey() { return siteKey; } public void setSiteKey(String siteKey) { this.siteKey = siteKey; } @Column(name = "Site", unique = true, length = 125, nullable = false) public String getSite() { return site; } public void setSite(String site) { this.site = site; } @Column(name = "SiteType", unique = false, length = 8, nullable = true) public String getSiteType() { return siteType; } public void setSiteType(String siteType) { this.siteType = siteType; } @Column(name = "Address1", unique = false, length = 125, nullable = true) public String getAddress1() { return address1; } public void setAddress1(String address1) { this.address1 = address1; } @Column(name = "Address2", unique = false, length = 125, nullable = true) public String getAddress2() { return address2; } public void setAddress2(String address2) { this.address2 = address2; } @Column(name = "City", unique = false, length = 125, nullable = true) public String getCity() { return city; } public void setCity(String city) { this.city = city; } @Column(name = "ZipCode", unique = false, length = 50, nullable = true) public String getZipCode() { return zipCode; } public void setZipCode(String zipCode) { this.zipCode = zipCode; } @Column(name = "CreatedBy", unique = false, length = 125, nullable = true) public String getCreatedBy() { return createdBy; } public void setCreatedBy(String createdBy) { this.createdBy = createdBy; } @Column(name = "GLCode", unique = false, length = 11, nullable = true) public String getGlCode() { return glCode; } public void setGlCode(String glCode) { this.glCode = glCode; } }
Example
public class SiteJsonator extends Jsonator<Site> { public SiteJsonator() { super(Site.class); } } @Controller @RequestMapping(value = "/sites") public class SitesController { @Autowired private SiteService siteService; @RequestMapping(value = "/", method = RequestMethod.GET, headers = "Accept=application/json") @ResponseBody public String index(ModelMap map) { SiteJsonator list = new SiteJsonator();; try { list.convert(siteService.getAll()); return list.results(); } catch (Exception ex) { return list.error(); } } }
UPDATE 2
Here is the best Jsonator for those interested:
https://gist.github.com/3893242
You can pass the string "exclude" String [] and not include them. In addition, it has standard “results, messages, etc.,” which we would like to convey in our AJAX requests. Good for ExtJS.