I am using the #JsonProperty(name = "property_name") (Jackson) annotation wherever the property name in the json is different from the property name in my object. Is there a way I can programmatically access this information somewhere else in code?
Example:
public class Entity {
protected long entityName;
#JsonProperty("entity_name")
public long getEntityName() {
return entityName;
}
public void setEntityName(String entityName) {
this.entityName = entityName;
}
}
What I need is a method to map entity_name to entityName. e.g, getActualFieldName("entity_name") should return "entityName". I can keep a separate file with all these mappings, but I don't want to do that because this information is already present in the form of #JsonProperty annotations. If I can extract it from there somehow, it would simplify things a bit.
Check this Helper utility. getAnnotationParameter
Related
I need to ignore the field when return the response from spring boot. Pls find below info,
I have one pojo called Student as below
Student {
id,
name,
lastName
}
i am getting a body for as PostRequest as below
{
id:"1",
name:"Test",
lname:"Test"
}
i want get all the data from frontEnd (id,name,Lname) But i just want to return the same pojo class without id as below,
{
name:"Test",
lName:"Test"
}
I have tried #JsonIgnore for column id, But it makes the id column as null(id=null -it is coming like this even when i send data to id field from postman) when i get the data from frontEnd.
I would like to use only one pojo to get the data with proper data(withoud getting id as Null), and need to send back the data by ignoring the id column.
Is there any way to achieve it instead of using another pojo?
You just need to use #JsonInclude(JsonInclude.Include.NON_NULL) at class level and it will be helpful for ignore all your null fields.
For example :
#JsonInclude(JsonInclude.Include.NON_NULL)
public class Test {
// Fields
// Constructors
// Getters - setters
}
As of now you are using only one POJO it's not good practice because it's your main entity into your project, so good practice is always make DTO for the same.
This is possible via the #JsonView annotation that is part of Jackson. Spring can leverage it to define the views used on the controller.
You'd define your DTO class like this:
class User {
User(String internalId, String externalId, String name) {
this.internalId = internalId;
this.externalId = externalId;
this.name = name;
}
#JsonView(User.Views.Internal.class)
String internalId;
#JsonView(User.Views.Public.class)
String externalId;
#JsonView(User.Views.Public.class)
String name;
static class Views {
static class Public {
}
static class Internal extends Public {
}
}
}
The Views internal class acts as a marker to jackson, in order to tell it which fields to include in which configuration. It does not need to be an inner class, but that makes for a shorter code snippet to paste here. Since Internal extends Public, all fields marked with Public are also included when the Internal view is selected.
You can then define a controller like this:
#RestController
class UserController {
#GetMapping("/user/internal")
#JsonView(User.Views.Internal.class)
User getPublicUser() {
return new User("internal", "external", "john");
}
#GetMapping("/user/public")
#JsonView(User.Views.Public.class)
User getPrivateUser() {
return new User("internal", "external", "john");
}
}
Since Spring is aware of the JsonView annotations, the JSON returned by the /public endpoint will contain only externalId and name, and the /internal endpoint will additionally include the internalId field.
Note that fields with no annotation will not be included if you enable any view. This behaviour can be controlled by MapperFeature.DEFAULT_VIEW_INCLUSION, which was false in the default Spring ObjectMapper when I used this for the last time.
You can also annotate your #RequestBody parameters to controller methods with JsonView, to allow/disallow certain parameters on input objects, and then use a different set of parameters for output objects.
I am creating a requestModel and let say a person doesn't send me some keys.
If that key is not present I want to put null if i get the value of the key.
I don't want to investigate if a key is present or not .
public class CustomerModel {
private Optional<String> s3Bucket;
private Optional<String> docType;
public String getS3Bucket() {
if(s3Bucket.isPresent()) {
return s3Bucket.get();
} else {
return null;
}
}
public void setS3Bucket(Optional<String> s3Bucket) {
this.s3Bucket = s3Bucket;
}
public Optional<String> getDocType() {
return docType;
}
public void setDocType(Optional<String> docType) {
this.docType = docType;
}
}
Do we have any library or something where.
1. If i get the key and it is not present in the coming request json, i will get the null out of it and if the key is present and has value . It will be stored as value.
2. When writing the getter for s3bucket (getS3Bucket), i dont want to write it for everykey value. Is there a automatic way to do this.
I looked at lot of posts but the scenario is not there.
P.S - I am new to java
I believe Jackson is exactly what you need. And if you are using Spring - it already uses Jackson under the hood I guess.
Here you can find some examples and documentation of how JSON mapping on to model class is done.
If you need to customize some behavior, you can use annotations like #JsonProperty (there are many).
If properties in your model class have the same names as properties in JSON, most probably you won't need to provide any further configs.
Here is a simple example:
public class User {
#JsonProperty("userName")
private String name;
private int age;
// getters and setters
}
And if you have JSON like this:
{
"userName" : "Foo Bar",
"age" : 18
}
Jackson will do all the magic for you unless you need something very specific.
If something is not in JSON you get (let's say you received JSON without age) - corresponding property in model class will be null if it is object type and default value (0, false, etc.) for primitives (in our case age would be 0).
I have a java api which performs an external resource lookup and then maps the values to a Pojo. To do this, the api needs the field names of the Pojo as string values, something like:
public <F> F populatePojoFields(String primaryField, String secondaryField);
This works fine, however passing the pojo field names as String to the api does not feel right. I was able to change this by writing marker annotations for the pojo, so now it is like
public class POJO {
#Primary //custom marker annotation
private int mojo;
#Secondary //custom marker annotation
private String jojo;
}
String primaryField = getFieldNameUsingReflection(Pojo.class, Primary.class)
String secondryField = getFieldNameUsingReflection(Pojo.class, Secondary.class)
Pojo pojo = populatePojoFields(primaryField, secondaryField);
This way I don't have to keep track of string values, I can just add marker annotations to the Pojo fields. This works fine, but I'm worried about performance. Is this a standard way to do things? as keeping hardcoded string values is more efficient than looking up the field names every time we need to call the api. Is there a better way to do this?
If you call getFieldNameUsingReflection often you can think to cache the result of this call.
You can use a singleton class with internal Map with a code like the following:
public class SingletonMapPrimarySecondary {
Map<Class, String> mapPrimary;
Map<Class, String> mapSecondary;
// TODO: Handle mapPrimary and mapSecondary creation and singleton pattern
public String getPrimary(Class clazz) {
String primary = mapPrimary.get(clazz);
if (primary == null) {
primary = getFieldNameUsingReflection(clazz, Primary.class);
mapPrimary.put(clazz, primary);
}
return primary;
}
public String getSecondary(Class clazz) {
// TODO: Similar to getPrimary
}
}
In Java, I have access to value of Transient fields of the class. However, I do not access to the same fields on JSP. How can I make them available to JSP?
I am retrieving the values using Hibernate, I reckon a solution to this would be to Transformers.aliasToBean option but is there any other solution to it?
Is there anyway to get rid of transient annotation but have the same mapping in Hibernate? In that case, the problem will be solved.
#AssociationOverrides({
#AssociationOverride(name = "tta.names", joinColumns = #JoinColumn(name = "id"))})
public class Names implements java.io.Serializable {
private static final long serialVersionUID = -30956546435023625398L;
#EmbeddedId
private TableToAssociate tta = new TableToAssociate();
#Transient
public String getid() {
return tta.getMyIds().getId();
}
public void setid(String id) {
this.tta.getMyIds().setId(id);
}
In Java, I can access them using following code
System.out.println(mystudents.getNames().iterator().next().getId());
In JSP, I do not have access to them!
<c:forEach var="nm"items="${mystudents.names}">
${nm.id}
</c:forEach>
If I put another field of names that is not transient, JSP successfully show the value of that item.
Try renaming the methods to match the JavaBean specification.
Instead of:
#Transient
public String getid() {
return tta.getMyIds().getId();
}
public void setid(String id) {
this.tta.getMyIds().setId(id);
}
you should have:
#Transient
public String getId() {
return tta.getMyIds().getId();
}
public void setId(String id) {
this.tta.getMyIds().setId(id);
}
Get rid of #Transient on your entity. Based on your embedded id, you've chosen field annotations. You should be able to have a getter that Hibernate won't try to persist without explicitly marking it as such. And change the getter/setter to use correct JavaBean syntax. getId instead of getid.
It is happening because transient keyword stops the field to be serialized. To pass an object to JSP, it must be serialized. This field will not be there in your serialized object and hence, it is not available to JSP.
For solving your problem, you should see James' comment to use #Transient annotation. It is supplied by JPA and it should allow you to NOT save your value in DB, but serialize it so your JSP can use it.
What you are asking is not possible.. As smarter then me said before.
#Transient is just saying not to serialize/deserialize. Hibernate doesn't serialize this and the same is what jsp bean.
You can do several things:
I think the best thing here is to wrap field in getter and setter in the bean.. This way you will set the property on the bean and in case of only one field every other solution will be overhead.
public class Bean() {
private Names name;
private String id;
public Bean() {
//few action to load name
this.id = name.getid();
}
public String getId() {
return this.id;
}
Create different entity for ui(Bean) and DB(Hibernate). In many cases ui layer and entities are not the same and sometime should not be coupled
You can use inheritance and create diffrent implemenation in the hibernate entity and on ui layer(Jsp bean)
If you ask me i think the best is to do what on section 1. If this happen more oftain you should consider decouple your ui layer and business entity.
I'm migrating a legacy system over to use Hibernate 3. It currently generates its own identifiers. To keep with what the system currently does before I try and move it over to something a little better, how would I go about specifying (using annotations) my own class that will return the custom generated identifiers when an insert occurs?
Something like:
#Id
#CustomIdGenerator(Foo.class) // obviously this is not a real annotation
public String getId() { ... }
Where the Foo class has one method that generates the identifier.
Currently I'm just calling the setId(String id) method manually but was hoping for a better way to deal with this situation.
I don't think there is out-of-box support for generating custom Ids using custom annotations using pure JPA-2 API. But if you want to use provider specific API, then the job is pretty simple. Sample Example
To be provider independent try any of following tricks....
IdGeneratorHolder
public abstract class IdGeneratorHolder {
/* PersistentEntity is a marker interface */
public static IdGenerator getIdGenerator(Class<? extends PersistentEntity> entityType) {
/* sample impelementation */
if(Product.class.isAssignableFrom(entityType)) {
return new ProductIdGenerator();
}
return null;
}
}
General IdGenerator interface
public interface IdGenerator {
String generate();
}
Specific IdGenerator - Product Id Generator
public class ProductIdGenerator implements IdGenerator {
public String generate() {
/* some complicated logic goes here */
return ${generatedId};
}
}
Now set the generated id either in no-arg constructor OR in #PrePersist method.
Product.java
public class Product implements PersistentEntity {
private String id;
public Product() {
id = IdGeneratorHolder.getIdGenerator(getClass()).generate();
}
#PrePersist
public void generateId() {
id = IdGeneratorHolder.getIdGenerator(getClass()).generate();
}
}
In above example all the ids are of the same type i.e. java.lang.String. If the persistent entities have ids of different types.....
IdGenerator.java
public interface IdGenerator {
CustomId generate();
}
CustomId.java
public class CustomId {
private Object id;
public CustomId(Object id) {
this.id = id;
}
public String toString() {
return id.toString();
}
public Long toLong() {
return Long.valueOf(id.toString());
}
}
Item.java
#PrePersist
public void generateId() {
id = IdGeneratorHolder.getIdGenerator(getClass()).generate().toLong();
}
You can also use your custom annotation...
CustomIdGenerator.java
public #interface CustomIdGenerator {
IdStrategy strategy();
}
IdStrategy.java
enum IdStrategy {
uuid, humanReadable,
}
IdGeneratorHolder.java
public abstract class IdGeneratorHolder {
public static IdGenerator getIdGenerator(Class<? extends PersistentEntity> entityType) {
try { // again sample implementation
Method method = entityType.getMethod("idMethod");
CustomIdGenerator gen = method.getAnnotation(CustomIdGenerator.class);
IdStrategy strategy = gen.strategy();
return new ProductIdGenerator(strategy);
}
One more thing.... If we set id in #PrePersist method, the equals() method cannot rely on id field (i.e. surrogate key), we have to use business/natural key to implement equals() method. But if we set id field to some unique value (uuid or "app-uid" unique within application) in no-arg constructor, it helps us to implement the equals() method.
public boolean equals(Object obj) {
if(obj instanceof Product) {
Product that = (Product) obj;
return this.id ==that.id;
}
return false;
}
If we or someone else call (intentionally or by mistake) the #PrePersist annotated method more than one times, the "unique id will be changed!!!" So setting id in no-arg constructor is preferable. OR to address this issue put a not null check...
#PrePersist
public void generateId() {
if(id != null)
id = IdGeneratorHolder.getIdGenerator(getClass()).generate();
}
}
UPDATE
If we put the id generation in a
no-arg constructor, wouldn't that
cause a problem when loading entities
from the database? because hibernate
will call the no-arg constructor
causing existing ids to be
re-generated
Yeah you are right, I missed that part. :( Actually, I wanted to tell you that:- in my application every Entity object is associated with an Organization Entity; so I've created an abstract super class with two constructors, and every Entity (except Organization) extends this class.
protected PersistentEntityImpl() {
}
protected PersistentEntityImpl(Organization organization) {
String entityId = UUIDGenerator.generate();
String organizationId = organization.getEntityId();
identifier = new EntityIdentifier(entityId, organizationId);
}
The no-arg constructor is for JPA provider, we never invoke no-arg constructor, but the other organization based constructor. As you can see. id is assigned in Organization based constructor. (I really missed this point while writing the answer, sorry for that).
See if you can implement this or similar strategy in your application.
The second option was using the
#PrePersist annotation. I put that in
and the method never got hit and gave
me an exception stating that I needed
to set the id manually. Is there
something else I should be doing?
Ideally, JPA provider should invoke #PrePersist methods (one declared in class and also all the other methods that are declared in super-classes) before persisting the entity object. Can't tell you what is wrong, unless you show some code and console.
You can.
First, implement org.hibernate.id.IdentifierGenerator
Then you'd have to map it in a mapping xml file. I couldn't find a way to do this with annotations:
<!--
<identifier-generator.../> allows customized short-naming
of IdentifierGenerator implementations.
-->
<!ELEMENT identifier-generator EMPTY>
<!ATTLIST identifier-generator name CDATA #REQUIRED>
<!ATTLIST identifier-generator class CDATA #REQUIRED>
Finally, use #GeneratedValue(generator="identifier-name")
Note that this is hibernate-specific (not JPA)
Update: I took a look at the sources of Hibernate, and it seems at one place, after failing to resolve the short name, hibernates attempts to call Class.forName(..). The parameter there is called strategy. So Here's what you try:
try setting the class fully-qualified name as string in the generator attribute
try setting the class fqn as string in the #GenericGenerator strategy attribute (with some arbitrary name)
Let me know which (if any) worked