如何将JSON主体中的数组映射到POJO？

Question

I'm implementing many-to-many relationship using hibernate as JPA and spring-boot. When I do a post request from the POSTMAN, I get the following error:

Failed to convert from type [java.net.URI] to type [com.domain.Datasource]

There is a many to many relationship between Metric and Datasource .

JSON body

{
    "companyId" : "fake_company_id",
    "name" : "test_name",
    "description" :"test Description",
    "datasources" :  ["fdaea7d4162bd2c3f3db5ba059638123"]
}

Metric.java

@Entity
public class Metric implements Persistable<Long> {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(nullable = false)
@RestResource(exported = false)
private Long id;

@Column(nullable = false, unique = true)
private String publicId;
@Column(nullable = false)
private String name;
private MetricType type;

@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "metric_datasource", joinColumns = @JoinColumn(name = "metric_id", referencedColumnName = "id"), inverseJoinColumns =  @JoinColumn(name = "datasource_id", referencedColumnName = "id"))
private Set<Datasource> datasources ;
private String definition;
private long dateCreated;
private String description;
private String companyId;

protected Metric() {
    this.dateCreated = new Date().getTime();
}

public Metric(String name, String publicId, String definition) {
    super();
    this.name = name;
    this.publicId = publicId;
    this.definition = definition;
}

@JsonIgnore
@Override
public boolean isNew() {
    return null == getId();
}

@PrePersist
public void generatePublicId() {
    publicId = PublicIdGenerator.generate(32);
}

@Override
public Long getId() {
    return id;
}

public String getPublicId() {
    return publicId;
}

public void setPublicId(String publicId) {
    this.publicId = publicId;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getDefinition() {
    return definition;
}

public void setDefinition(String definition) {
    this.definition = definition;
}

public void setDateCreated(long dateCreated) {
    this.dateCreated = dateCreated;
}

public long getDateCreated(){
    return this.dateCreated;
}

public String getDescription() {
    return description;
}

public void setDescription(String description) {
    this.description = description;
}

public Set<Datasource> getDatasources() {
    if (datasources != null) {
        return datasources;
    } else {
        return Collections.emptySet();
    }
}

public void setDatasources(Set<Datasource> datasources) {
    if (datasources != null) {
        this.datasources = datasources;
    } else {
        this.datasources = Collections.emptySet();
    }
}

public void setId(Long id) {
    this.id = id;
}

public String getCompanyId() {
    return companyId;
}

public void setCompanyId(String companyId) {
    this.companyId = companyId;
}

public MetricType getType() {
    return type;
}

public void setType(MetricType type) {
    this.type = type;
}

public void update(Metric metric) {
    if (metric.getName() != null) {
        setName(metric.getName());
    }

    if (metric.getDescription() != null) {
        setDescription(metric.getDescription());
    }
    if (metric.getDefinition() != null) {
        setDefinition(metric.getDefinition());
    }
}

Datasource.java

@Entity
public class Datasource implements Persistable<Long> {

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

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(nullable = false)
@RestResource(exported = false)
private Long id;

@ManyToMany(mappedBy = "datasources")
private Set<Metric> metrics;

public Datasource() {
    this(null);
}

public Datasource(String publicId) {
    this.publicId = publicId;
}

public String getPublicId() {
    return publicId;
}

public void setPublicId(String publicId) {
    this.publicId = publicId;
}

@Override
public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

@Override
public boolean isNew() {
    return null == getId();
}

public Set<Metric> getMetrics() {
    return metrics;
}

public void setMetrics(Set<Metric> metrics) {
    this.metrics = metrics;
}

Currently the relationship between Metric and Datasource is set properly , ie I have three tables metric , datasource and metric_datasource created in the database. But I'm not sure how can I save the value using the give JSON body. Please help.

Answer 1

First, make sure that method in your REST-controller can consume "application/json", has a proper @RequestBody annotation in it's arguments.
Second, I think sending a full-scale domain-like objects from client is not correct. You should implement DTO for class Metric that would fully match the JSON you've provided. And the datasources property should be List<String> containing the actual datasources' ids in that case.

Then you should implement a method in your that would convert DTO to domain object (where you can fetch DataSource objects for each datasource id stored in DTO) to persist it then.

// assuming that you already implemented any JpaRepository<Metric> interface
@Autowired
private MetricRepository metricRepo;

@Autowired
private DataSourceRepository dataSourceRepo;

public Metric saveMetricDTO(MetricDTO dto) {
  Metric metric = metricRepo.findByName(dto.getName()); // or fetch by any other suitable property
  // assign all props from DTO to metric: metric.setSmth(dto.getSmth())
  // ...
  List<DataSource> dsList = dto.getDataSourceIds().stream()
    .map(dataSourceRepo::findOne)
    .collect(Collectors.toList())
  metric.setDataSources(dsList);
  metricRepo.save(metric); // finally persist object
}