NullPointerException 尝试检索 @ManyToOne 父字段 - Spring Boot

Question

我正在尝试从 @ManyToOne 关系中的父实体获取一个字段，但是当我尝试打印父字段时，它在集成测试期间引发 NullPointerException，下面是我的两个实体的代码，包括测试。

相册实体 - 父级

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;

import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import javax.validation.constraints.NotBlank;

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table(name = "albuns")
public class Album {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "native")
    @GenericGenerator(name = "native", strategy = "native")
    private Long codigo;

    @NotBlank(message = "Erro: Certifique-se de digitar o nome do album.")
    @Column(nullable = false)
    private String nome;

    @OneToMany(mappedBy = "album", cascade = { CascadeType.PERSIST, CascadeType.REMOVE }, fetch = FetchType.EAGER)
    private List<Imagem> imagens = new ArrayList<>();

    @Column(name = "data_criacao", nullable = false)
    private LocalDate dataCriacao;

    @Column(unique = true, nullable = false)
    private String capa;

    protected Album() {
    }

    public Album(String nome, LocalDate dataCriacao, String capa) {
        this.nome = nome;
        this.dataCriacao = dataCriacao;
        this.capa = capa;
    }

    public Long getCodigo() {
        return codigo;
    }

    public void setCodigo(Long codigo) {
        this.codigo = codigo;
    }

    public String getNome() {
        return nome;
    }

    public void setNome(String nome) {
        this.nome = nome;
    }

    public LocalDate getDataCriacao() {
        return dataCriacao;
    }

    public void setDataCriacao(LocalDate dataCriacao) {
        this.dataCriacao = dataCriacao;
    }

    public String getCapa() {
        return capa;
    }

    public void setCapa(String capa) {
        this.capa = capa;
    }

    public List<Imagem> getImagens() {
        return imagens;
    }

    public void setImagens(List<Imagem> imagens) {
        this.imagens = imagens;
    }

}

Imagem 实体 - 子项

import java.time.LocalDate;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.Table;

import org.hibernate.annotations.GenericGenerator;

@Entity
@Table(name = "imagens")
public class Imagem {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO, generator = "native")
    @GenericGenerator(name = "native", strategy = "native")
    private long codigo;

    @Column(nullable = false, unique = true)
    private String url;

    @Column(name = "data_carregamento", nullable = false)
    private LocalDate dataCarregamento;

    @ManyToOne(targetEntity = Album.class, fetch = FetchType.LAZY)
    @JoinColumn(name = "cod_album")
    private Album album;

    public Imagem() {
    }

    public Imagem(String url, LocalDate dataCarregamento) {
        this.url = url;
        this.dataCarregamento = dataCarregamento;

    }

    public long getCodigo() {
        return codigo;
    }

    public void setCodigo(long codigo) {
        this.codigo = codigo;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public LocalDate getDataCarregamento() {
        return dataCarregamento;
    }

    public void setDataCarregamento(LocalDate dataCarregamento) {
        this.dataCarregamento = dataCarregamento;
    }

    public Album getAlbum() {
        return album;
    }

    public Long getAlbumCodigo() {
        return album.getCodigo();
    }

    public void setAlbum(Album album) {
        this.album = album;
    }

}

专辑库

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import com.servidor.multiplatform.entidades.Album;

@Repository
public interface AlbumRepositorio extends JpaRepository<Album, Long> {

    public Album findByNome(String nome);

}

集成测试

import static org.assertj.core.api.Assertions.assertThat;

import java.time.LocalDate;
import java.util.ArrayList;
import java.util.List;

import org.junit.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
import org.springframework.boot.test.autoconfigure.orm.jpa.TestEntityManager;
import org.springframework.test.context.junit4.SpringRunner;

import com.servidor.multiplatform.entidades.Album;
import com.servidor.multiplatform.entidades.Imagem;
import com.servidor.multiplatform.repositorios.AlbumRepositorio;

@RunWith(SpringRunner.class)
@DataJpaTest
public class TesteDeIntegracaoAlbumRepositorio {

    @Autowired
    private TestEntityManager entityManager;

    @Autowired
    private AlbumRepositorio albumRepositorio;

    @Test
    public void TesteDeInsercaoDoAlbumAsSuasImagensEPesquisaDaSuaInformacao() {

        // Album

        Album album1 = new Album("Album 1", LocalDate.now(), "Capa 1");

        // List for Test
        List<Imagem> imagensLocal = new ArrayList<>();

        // Filling the Lists with new images
        for (int i = 0; i < 4; i++) {
            Imagem imagem = new Imagem("url" + i, LocalDate.now());
            imagensLocal.add(imagem);
            album1.getImagens().add(imagem);
        }

        // Persisting the Album and the Pictures
        entityManager.persist(album1);
        entityManager.flush();

        // Getting the Album and the Pictures

        Album albumEncontrado = albumRepositorio.findByNome("Album 1");
        List<Imagem> imagensPesistidas = albumEncontrado.getImagens();

        Album album = entityManager.find(Album.class, 1L);

        System.out.println(album.getCodigo());

        for (Imagem imagem : album.getImagens()) {
            // The problem is here in this code
            System.out.println(imagem.getAlbumCodigo());
        }

        // Testing the Album
        assertThat(album1.getNome()).isEqualTo(albumEncontrado.getNome());

        // Testing the Lists
        Assert.assertEquals(imagensLocal, imagensPesistidas);

    }

}

堆栈跟踪

TesteDeIntegracaoAlbumRepositorio.TesteDeInsercaoDoAlbumAsSuasImagensEPesquisaDaSuaInformacao
com.servidor.multiplatform.TesteDeIntegracaoAlbumRepositorio
TesteDeInsercaoDoAlbumAsSuasImagensEPesquisaDaSuaInformacao(com.servidor.multiplatform.TesteDeIntegracaoAlbumRepositorio)
java.lang.NullPointerException

    at com.servidor.multiplatform.entidades.Imagem.getAlbumCodigo(Imagem.java:75)

    at com.servidor.multiplatform.TesteDeIntegracaoAlbumRepositorio.TesteDeInsercaoDoAlbumAsSuasImagensEPesquisaDaSuaInformacao(TesteDeIntegracaoAlbumRepositorio.java:64)

    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)

    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

    at java.lang.reflect.Method.invoke(Unknown Source)

    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)

    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)

    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)

    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)

    at org.springframework.test.context.junit4.statements.RunBeforeTestExecutionCallbacks.evaluate(RunBeforeTestExecutionCallbacks.java:74)

    at org.springframework.test.context.junit4.statements.RunAfterTestExecutionCallbacks.evaluate(RunAfterTestExecutionCallbacks.java:84)

    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)

    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)

    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)

    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)

    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:251)

    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:97)

    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)

    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)

    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)

    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)

    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)

    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)

    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)

    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)

    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:190)

    at org.junit.runner.JUnitCore.run(JUnitCore.java:137)

    at org.junit.runner.JUnitCore.run(JUnitCore.java:115)

    at org.junit.vintage.engine.execution.RunnerExecutor.execute(RunnerExecutor.java:40)

    at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(Unknown Source)

    at java.util.stream.ReferencePipeline$3$1.accept(Unknown Source)

    at java.util.Iterator.forEachRemaining(Unknown Source)

    at java.util.Spliterators$IteratorSpliterator.forEachRemaining(Unknown Source)

    at java.util.stream.AbstractPipeline.copyInto(Unknown Source)

    at java.util.stream.AbstractPipeline.wrapAndCopyInto(Unknown Source)

    at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(Unknown Source)

    at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(Unknown Source)

    at java.util.stream.AbstractPipeline.evaluate(Unknown Source)

    at java.util.stream.ReferencePipeline.forEach(Unknown Source)

    at org.junit.vintage.engine.VintageTestEngine.executeAllChildren(VintageTestEngine.java:80)

    at org.junit.vintage.engine.VintageTestEngine.execute(VintageTestEngine.java:71)

    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:229)

    at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$6(DefaultLauncher.java:197)

    at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:211)

    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:191)

    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:137)

    at org.eclipse.jdt.internal.junit5.runner.JUnit5TestReference.run(JUnit5TestReference.java:89)

    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41)

    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541)

    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763)

    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463)

    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209)

Answer 1

Imagem.album 保持为空，因为单元测试中给出的代码从不写入该字段。只有一侧的关系是通过album1.getImagens().add(imagem) 设置的。

//Imagem.album is not set in this loop:
for (int i = 0; i < 4; i++) {
    Imagem imagem = new Imagem("url" + i, LocalDate.now());
    imagensLocal.add(imagem);
    album1.getImagens().add(imagem);
}

如规范中所述，应保持关系一致：

请注意，应用程序负责维护运行时关系的一致性——例如，确保双向关系的“单”和“多”边在以下情况下相互一致应用程序在运行时更新关系

对于albumEncontrado和album，它也将保持为空，因为它们是对与album1相同的对象的引用。之所以如此，是因为持久性上下文在任何时候都不会被清除。

解决问题的正确方法是通过设置关系的双方来保持关系一致：

for (int i = 0; i < 4; i++) {
    Imagem imagem = new Imagem("url" + i, LocalDate.now());
    imagensLocal.add(imagem);
    album1.getImagens().add(imagem);
    imagem.setAlbum(album1);
}

NullPointerException 也可以通过在查询数据库之前通过EntityManager.clear() 清除持久性上下文来避免。这将打破列表相等的断言，因为它取决于列表中元素的身份。原因是Imagem 没有实现equals。即使添加了equals，它仍然对元素的顺序有假设，这不是确定性的。