Как произвести извлечение JSON формата из PostgreSQL правильным образом через NetBeans?

112

15 марта 2022, 03:20

Я использую EclipseLink JPA 2.1. в NetBeans.

Создал табличку в БД PostgreSQL:

CREATE TABLE public.test_json (
    id serial NOT NULL,
    json_data json NOT NULL,
    CONSTRAINT test_json_pkey PRIMARY KEY (id)
);

В NetBeans выполнил команду "Entity Classes From DataBase", и попытался произвести отражение табличного представления из БД на мой Entity класс.

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package javaapplication6;
import java.io.Serializable;
import java.sql.Clob;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import javax.xml.bind.annotation.XmlRootElement;
/**
 *
 * @author ramze
 */
@Entity
@Table(name = "test_geometry")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "TestGeometry.findAll", query = "SELECT t FROM TestGeometry t")
    , @NamedQuery(name = "TestGeometry.findById", query = "SELECT t FROM TestGeometry t WHERE t.id = :id")})
public class TestGeometry implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "id")
    private Integer id;
    @Lob
    @Column(name = "geom")
    private Object geom;
    public TestGeometry() {
    }
    public TestGeometry(Integer id) {
        this.id = id;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public Object getGeom() {
        return geom;
    }
    public void setGeom(Serializable geom) {
        this.geom = geom;
    }
    @Override
    public int hashCode() {
        int hash = 0;
        hash += (id != null ? id.hashCode() : 0);
        return hash;
    }
    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof TestGeometry)) {
            return false;
        }
        TestGeometry other = (TestGeometry) object;
        if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
            return false;
        }
        return true;
    }
    @Override
    public String toString() {
        return "javaapplication6.TestGeometry[ id=" + id + " ]";
    }
}

После того как это было успешно выполнено, я попытался присоединиться к моей БД и извлечь оттуда информацию:

EntityManagerFactory emf = Persistence.createEntityManagerFactory("Name_of_my_connection");

где Name_of_my_connection = 'JavaApplication5PU'

Но Java не понимает JSON формат и выдала мне следующую ошибку.

debug:
Exception in thread "main" Local Exception Stack: 
Exception [EclipseLink-30005] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.PersistenceUnitLoadingException
Exception Description: An exception was thrown while searching for persistence archives with ClassLoader: sun.misc.Launcher$AppClassLoader@18b4aac2
Internal Exception: javax.persistence.PersistenceException: Exception [EclipseLink-28018] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.EntityManagerSetupException
Exception Description: Predeployment of PersistenceUnit [JavaApplication5PU] failed.
Internal Exception: Exception [EclipseLink-7164] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.ValidationException
Exception Description: The type [class java.lang.Object] for the attribute [jsonData] on the entity class [class javaapplication5.TestJson] is not a valid type for a lob mapping. For a lob of type BLOB, the attribute must be defined as a java.sql.Blob, byte[], Byte[] or a Serializable type. For a lob of type CLOB, the attribute must be defined as a java.sql.Clob, char[], Character[] or String type.
    at org.eclipse.persistence.exceptions.PersistenceUnitLoadingException.exceptionSearchingForPersistenceResources(PersistenceUnitLoadingException.java:127)
    at org.eclipse.persistence.jpa.PersistenceProvider.createEntityManagerFactoryImpl(PersistenceProvider.java:107)
    at org.eclipse.persistence.jpa.PersistenceProvider.createEntityManagerFactory(PersistenceProvider.java:177)
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:79)
    at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:54)
    at javaapplication5.JavaApplication5.main(JavaApplication5.java:23)
Caused by: javax.persistence.PersistenceException: Exception [EclipseLink-28018] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.EntityManagerSetupException
Exception Description: Predeployment of PersistenceUnit [JavaApplication5PU] failed.
Internal Exception: Exception [EclipseLink-7164] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.ValidationException
Exception Description: The type [class java.lang.Object] for the attribute [jsonData] on the entity class [class javaapplication5.TestJson] is not a valid type for a lob mapping. For a lob of type BLOB, the attribute must be defined as a java.sql.Blob, byte[], Byte[] or a Serializable type. For a lob of type CLOB, the attribute must be defined as a java.sql.Clob, char[], Character[] or String type.
    at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.createPredeployFailedPersistenceException(EntityManagerSetupImpl.java:1954)
    at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.predeploy(EntityManagerSetupImpl.java:1945)
    at org.eclipse.persistence.internal.jpa.deployment.JPAInitializer.callPredeploy(JPAInitializer.java:98)
    at org.eclipse.persistence.jpa.PersistenceProvider.createEntityManagerFactoryImpl(PersistenceProvider.java:96)
    ... 4 more
Caused by: Exception [EclipseLink-28018] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.EntityManagerSetupException
Exception Description: Predeployment of PersistenceUnit [JavaApplication5PU] failed.
Internal Exception: Exception [EclipseLink-7164] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.ValidationException
Exception Description: The type [class java.lang.Object] for the attribute [jsonData] on the entity class [class javaapplication5.TestJson] is not a valid type for a lob mapping. For a lob of type BLOB, the attribute must be defined as a java.sql.Blob, byte[], Byte[] or a Serializable type. For a lob of type CLOB, the attribute must be defined as a java.sql.Clob, char[], Character[] or String type.
    at org.eclipse.persistence.exceptions.EntityManagerSetupException.predeployFailed(EntityManagerSetupException.java:230)
    ... 8 more
Caused by: Exception [EclipseLink-7164] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.ValidationException
Exception Description: The type [class java.lang.Object] for the attribute [jsonData] on the entity class [class javaapplication5.TestJson] is not a valid type for a lob mapping. For a lob of type BLOB, the attribute must be defined as a java.sql.Blob, byte[], Byte[] or a Serializable type. For a lob of type CLOB, the attribute must be defined as a java.sql.Clob, char[], Character[] or String type.
    at org.eclipse.persistence.exceptions.ValidationException.invalidTypeForLOBAttribute(ValidationException.java:1132)
    at org.eclipse.persistence.internal.jpa.metadata.converters.LobMetadata.process(LobMetadata.java:124)
    at org.eclipse.persistence.internal.jpa.metadata.accessors.mappings.MappingAccessor.processLob(MappingAccessor.java:1707)
    at org.eclipse.persistence.internal.jpa.metadata.accessors.mappings.BasicAccessor.processLob(BasicAccessor.java:524)
    at org.eclipse.persistence.internal.jpa.metadata.accessors.mappings.MappingAccessor.processMappingConverter(MappingAccessor.java:1771)
    at org.eclipse.persistence.internal.jpa.metadata.accessors.mappings.MappingAccessor.processMappingValueConverter(MappingAccessor.java:1796)
    at org.eclipse.persistence.internal.jpa.metadata.accessors.mappings.BasicAccessor.process(BasicAccessor.java:419)
    at org.eclipse.persistence.internal.jpa.metadata.MetadataDescriptor.processMappingAccessors(MetadataDescriptor.java:1536)
    at org.eclipse.persistence.internal.jpa.metadata.accessors.classes.ClassAccessor.processMappingAccessors(ClassAccessor.java:1648)
    at org.eclipse.persistence.internal.jpa.metadata.accessors.classes.EntityAccessor.processMappingAccessors(EntityAccessor.java:1234)
    at org.eclipse.persistence.internal.jpa.metadata.accessors.classes.EntityAccessor.process(EntityAccessor.java:697)
    at org.eclipse.persistence.internal.jpa.metadata.MetadataProject.processStage2(MetadataProject.java:1793)
    at org.eclipse.persistence.internal.jpa.metadata.MetadataProcessor.processORMMetadata(MetadataProcessor.java:576)
    at org.eclipse.persistence.internal.jpa.deployment.PersistenceUnitProcessor.processORMetadata(PersistenceUnitProcessor.java:585)
    at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.predeploy(EntityManagerSetupImpl.java:1869)
    ... 6 more
C:\Users\ramze\AppData\Local\NetBeans\Cache\8.2\executor-snippets\debug.xml:83: Java returned: 1
BUILD FAILED (total time: 4 seconds)

Подскажите, пожалуйста, что нужно сделать, чтобы исправить эту ошибку? Как правильным образом отразить табличное представление, где один из столбцов представляет собой JSON формат???

Answer 1

Короче, я сам решил это:

1) Вот моя таблица в базе:

2) В автоматически сформированном ORM-классе TestJson:

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package javaapplication5;
import java.io.Serializable;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import javax.xml.bind.annotation.XmlRootElement;
/**
 *
 * @author ramze
 */
@Entity
@Table(name = "test_json")
@XmlRootElement
@NamedQueries({
    @NamedQuery(name = "TestJson.findAll", query = "SELECT t FROM TestJson t")
    , @NamedQuery(name = "TestJson.findById", query = "SELECT t FROM TestJson t WHERE t.id = :id")})
public class TestJson implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "id")
    private Integer id;
    @Basic(optional = false)
    @Lob
    @Column(name = "json_data")
    private Object jsonData;
    public TestJson() {
    }
    public TestJson(Integer id) {
        this.id = id;
    }
    public TestJson(Integer id, Object jsonData) {
        this.id = id;
        this.jsonData = jsonData;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public Object getJsonData() {
        return jsonData;
    }
    public void setJsonData(Object jsonData) {
        this.jsonData = jsonData;
    }
    @Override
    public int hashCode() {
        int hash = 0;
        hash += (id != null ? id.hashCode() : 0);
        return hash;
    }
    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof TestJson)) {
            return false;
        }
        TestJson other = (TestJson) object;
        if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id))) {
            return false;
        }
        return true;
    }
    @Override
    public String toString() {
        return "javaapplication5.TestJson[ id=" + id + " ]";
    }
}

Изменил

@Lob
@Column(name = "json_data")
private Object jsonData;
public Object getJsonData() {
    return jsonData;
}

на

@Lob
@Column(name = "json_data")
private String jsonData;
public String getJsonData() {
    return jsonData;
}

Выполнил вот этот код:

EntityManagerFactory emf = Persistence.createEntityManagerFactory("JavaApplication5PU");
EntityManager em = emf.createEntityManager();
TestJson test_json = em.createNamedQuery("TestJson.findAll", TestJson.class).getSingleResult();

И в переменной test_json получил адекватный строковый json: