Most of
the time, in web application development, we need to define model classes in
sync with json payload. What if there is a way to generate model POJO classes using
json document…sounds nice right. In this post, I am going to explain how can
you generate Java POJOs using json document.
Follow
below step-by-step procedure to generate model classes.
Step 1:
Define an instance of
Jackson2Annotator. Jackson2Annotator class generates Java types using the
Jackson 2.x mapping annotations.
GenerationConfig generationConfig = new DefaultGenerationConfig() {
@Override
public boolean isGenerateBuilders() {
return true;
}
public SourceType getSourceType() {
return SourceType.JSON;
}
};
Jackson2Annotator jackson2Annotator = new Jackson2Annotator(generationConfig);
Step 2: Define SchemaMapper instance. SchemaMapper generates
Java types from a JSON schema. Can accept a factory which will be used to
create type generation rules for this mapper.
SchemaStore schemaStore = new SchemaStore();
RuleFactory ruleFactory = new RuleFactory(generationConfig, jackson2Annotator, schemaStore);
SchemaMapper mapper = new SchemaMapper(ruleFactory, new SchemaGenerator());
Step 3:
Reads schema and adds
generated types to the given code model.
JCodeModel jCodeModel = new JCodeModel();
File inputJson = new File(INPUT_JSON_FILE);
URL inputJsonURL = inputJson.toURI().toURL();
mapper.generate(jCodeModel, "Employee", PACKAGE_NAME, inputJsonURL);
If the
input file is located in classpath, you can get the file url using below
statement.
URL inputJsonURL = PojoFromJsonDocument.class.getClassLoader().getResource(INPUT_JSON_FILE);
Step 4:
Write the generated
types to the output directory.
File outputPojoDirectory = new File(OUTPUT_DIR);
outputPojoDirectory.mkdirs();
jCodeModel.build(outputPojoDirectory);
Find the
below working application.
employee.json
{
"id": 1,
"firstName": "Ram",
"lastName": "Gurram",
"address": {
"street": "Chowdeswari",
"city": "Bangalore",
"country": "India"
}
}
PojoFromJsonDocument.java
import java.io.File;
import java.io.IOException;
import java.net.URL;
import org.jsonschema2pojo.DefaultGenerationConfig;
import org.jsonschema2pojo.GenerationConfig;
import org.jsonschema2pojo.Jackson2Annotator;
import org.jsonschema2pojo.SchemaGenerator;
import org.jsonschema2pojo.SchemaMapper;
import org.jsonschema2pojo.SchemaStore;
import org.jsonschema2pojo.SourceType;
import org.jsonschema2pojo.rules.RuleFactory;
import com.sun.codemodel.JCodeModel;
public class PojoFromJsonDocument {
private static final String INPUT_JSON_FILE = "employee.json";
private static final String PACKAGE_NAME = "com.sample.app.model";
private static final String OUTPUT_DIR = "/Users/Shared/json/modelClasses";
public static void main(String[] args) throws IOException {
GenerationConfig generationConfig = new DefaultGenerationConfig() {
@Override
public boolean isGenerateBuilders() {
return true;
}
public SourceType getSourceType() {
return SourceType.JSON;
}
};
Jackson2Annotator jackson2Annotator = new Jackson2Annotator(generationConfig);
SchemaStore schemaStore = new SchemaStore();
RuleFactory ruleFactory = new RuleFactory(generationConfig, jackson2Annotator, schemaStore);
SchemaMapper mapper = new SchemaMapper(ruleFactory, new SchemaGenerator());
JCodeModel jCodeModel = new JCodeModel();
URL inputJsonURL = PojoFromJsonDocument.class.getClassLoader().getResource(INPUT_JSON_FILE);
mapper.generate(jCodeModel, "Employee", PACKAGE_NAME, inputJsonURL);
File outputPojoDirectory = new File(OUTPUT_DIR);
outputPojoDirectory.mkdirs();
jCodeModel.build(outputPojoDirectory);
}
}
Run the
application, you will see following messages in console.
com/sample/app/model/Address.java
com/sample/app/model/Employee.java
You can
observe Employee and Address classes are generated.
$tree /Users/Shared/json/modelClasses/
/Users/Shared/json/modelClasses/
└── com
└── sample
└── app
└── model
├── Address.java
└── Employee.java
4 directories, 2 files
Generated
source code
Address.java
package com.sample.app.model;
import java.util.HashMap;
import java.util.Map;
import javax.annotation.Generated;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
"street",
"city",
"country"
})
@Generated("jsonschema2pojo")
public class Address {
@JsonProperty("street")
private String street;
@JsonProperty("city")
private String city;
@JsonProperty("country")
private String country;
@JsonIgnore
private Map<String, Object> additionalProperties = new HashMap<String, Object>();
@JsonProperty("street")
public String getStreet() {
return street;
}
@JsonProperty("street")
public void setStreet(String street) {
this.street = street;
}
public Address withStreet(String street) {
this.street = street;
return this;
}
@JsonProperty("city")
public String getCity() {
return city;
}
@JsonProperty("city")
public void setCity(String city) {
this.city = city;
}
public Address withCity(String city) {
this.city = city;
return this;
}
@JsonProperty("country")
public String getCountry() {
return country;
}
@JsonProperty("country")
public void setCountry(String country) {
this.country = country;
}
public Address withCountry(String country) {
this.country = country;
return this;
}
@JsonAnyGetter
public Map<String, Object> getAdditionalProperties() {
return this.additionalProperties;
}
@JsonAnySetter
public void setAdditionalProperty(String name, Object value) {
this.additionalProperties.put(name, value);
}
public Address withAdditionalProperty(String name, Object value) {
this.additionalProperties.put(name, value);
return this;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append(Address.class.getName()).append('@').append(Integer.toHexString(System.identityHashCode(this))).append('[');
sb.append("street");
sb.append('=');
sb.append(((this.street == null)?"<null>":this.street));
sb.append(',');
sb.append("city");
sb.append('=');
sb.append(((this.city == null)?"<null>":this.city));
sb.append(',');
sb.append("country");
sb.append('=');
sb.append(((this.country == null)?"<null>":this.country));
sb.append(',');
sb.append("additionalProperties");
sb.append('=');
sb.append(((this.additionalProperties == null)?"<null>":this.additionalProperties));
sb.append(',');
if (sb.charAt((sb.length()- 1)) == ',') {
sb.setCharAt((sb.length()- 1), ']');
} else {
sb.append(']');
}
return sb.toString();
}
@Override
public int hashCode() {
int result = 1;
result = ((result* 31)+((this.country == null)? 0 :this.country.hashCode()));
result = ((result* 31)+((this.additionalProperties == null)? 0 :this.additionalProperties.hashCode()));
result = ((result* 31)+((this.city == null)? 0 :this.city.hashCode()));
result = ((result* 31)+((this.street == null)? 0 :this.street.hashCode()));
return result;
}
@Override
public boolean equals(Object other) {
if (other == this) {
return true;
}
if ((other instanceof Address) == false) {
return false;
}
Address rhs = ((Address) other);
return (((((this.country == rhs.country)||((this.country!= null)&&this.country.equals(rhs.country)))&&((this.additionalProperties == rhs.additionalProperties)||((this.additionalProperties!= null)&&this.additionalProperties.equals(rhs.additionalProperties))))&&((this.city == rhs.city)||((this.city!= null)&&this.city.equals(rhs.city))))&&((this.street == rhs.street)||((this.street!= null)&&this.street.equals(rhs.street))));
}
}
Employee.java
package com.sample.app.model;
import java.util.HashMap;
import java.util.Map;
import javax.annotation.Generated;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
"id",
"firstName",
"lastName",
"address"
})
@Generated("jsonschema2pojo")
public class Employee {
@JsonProperty("id")
private Integer id;
@JsonProperty("firstName")
private String firstName;
@JsonProperty("lastName")
private String lastName;
@JsonProperty("address")
private Address address;
@JsonIgnore
private Map<String, Object> additionalProperties = new HashMap<String, Object>();
@JsonProperty("id")
public Integer getId() {
return id;
}
@JsonProperty("id")
public void setId(Integer id) {
this.id = id;
}
public Employee withId(Integer id) {
this.id = id;
return this;
}
@JsonProperty("firstName")
public String getFirstName() {
return firstName;
}
@JsonProperty("firstName")
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public Employee withFirstName(String firstName) {
this.firstName = firstName;
return this;
}
@JsonProperty("lastName")
public String getLastName() {
return lastName;
}
@JsonProperty("lastName")
public void setLastName(String lastName) {
this.lastName = lastName;
}
public Employee withLastName(String lastName) {
this.lastName = lastName;
return this;
}
@JsonProperty("address")
public Address getAddress() {
return address;
}
@JsonProperty("address")
public void setAddress(Address address) {
this.address = address;
}
public Employee withAddress(Address address) {
this.address = address;
return this;
}
@JsonAnyGetter
public Map<String, Object> getAdditionalProperties() {
return this.additionalProperties;
}
@JsonAnySetter
public void setAdditionalProperty(String name, Object value) {
this.additionalProperties.put(name, value);
}
public Employee withAdditionalProperty(String name, Object value) {
this.additionalProperties.put(name, value);
return this;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append(Employee.class.getName()).append('@').append(Integer.toHexString(System.identityHashCode(this))).append('[');
sb.append("id");
sb.append('=');
sb.append(((this.id == null)?"<null>":this.id));
sb.append(',');
sb.append("firstName");
sb.append('=');
sb.append(((this.firstName == null)?"<null>":this.firstName));
sb.append(',');
sb.append("lastName");
sb.append('=');
sb.append(((this.lastName == null)?"<null>":this.lastName));
sb.append(',');
sb.append("address");
sb.append('=');
sb.append(((this.address == null)?"<null>":this.address));
sb.append(',');
sb.append("additionalProperties");
sb.append('=');
sb.append(((this.additionalProperties == null)?"<null>":this.additionalProperties));
sb.append(',');
if (sb.charAt((sb.length()- 1)) == ',') {
sb.setCharAt((sb.length()- 1), ']');
} else {
sb.append(']');
}
return sb.toString();
}
@Override
public int hashCode() {
int result = 1;
result = ((result* 31)+((this.firstName == null)? 0 :this.firstName.hashCode()));
result = ((result* 31)+((this.lastName == null)? 0 :this.lastName.hashCode()));
result = ((result* 31)+((this.id == null)? 0 :this.id.hashCode()));
result = ((result* 31)+((this.address == null)? 0 :this.address.hashCode()));
result = ((result* 31)+((this.additionalProperties == null)? 0 :this.additionalProperties.hashCode()));
return result;
}
@Override
public boolean equals(Object other) {
if (other == this) {
return true;
}
if ((other instanceof Employee) == false) {
return false;
}
Employee rhs = ((Employee) other);
return ((((((this.firstName == rhs.firstName)||((this.firstName!= null)&&this.firstName.equals(rhs.firstName)))&&((this.lastName == rhs.lastName)||((this.lastName!= null)&&this.lastName.equals(rhs.lastName))))&&((this.id == rhs.id)||((this.id!= null)&&this.id.equals(rhs.id))))&&((this.address == rhs.address)||((this.address!= null)&&this.address.equals(rhs.address))))&&((this.additionalProperties == rhs.additionalProperties)||((this.additionalProperties!= null)&&this.additionalProperties.equals(rhs.additionalProperties))));
}
}
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