Question

我正在尝试使用GSON将列表格式的java对象转换为JSON，我尝试了几种方法，但遇到了同样的错误。

第一次尝试

List<Techinv> techs = UserUtil.getTechModels(group, org);
Gson gson = new Gson();
String json = gson.toJson(techs);

第二次尝试

List<Techinv> techs = UserUtil.getTechModels(group, org);
Type listType = new TypeToken<List<Techinv>>() {}.getType();
Gson gson = new Gson();
String json = gson.toJson(techs, listType);

第3次尝试

List<Techinv> techs = UserUtil.getTechModels(group, org);
GsonBuilder gsonBuilder = new GsonBuilder();

new GraphAdapterBuilder()
    .addType(Techinv.class)
    .registerOn(gsonBuilder);
Gson gson = gsonBuilder.create();
String json = gson.toJson(techs);

以上所有内容都失败了，无论是stackoverflow error还是can't convert java int（我的Techinv类中的一个成员）都是一个java向量，都在GSON库中。

请告诉我，我在所有这些例子中都缺少一些简单的东西：）

Techinv课程（如果需要）

package org.cchit.inv.model;

import java.io.Serializable;
import java.util.Date;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.Lob;
import javax.persistence.ManyToOne;
import javax.persistence.NamedNativeQueries;
import javax.persistence.NamedNativeQuery;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import javax.persistence.Temporal;
import javax.persistence.TemporalType;


/**
 * The persistent class for the techinv database table.
 * 
 */
@Entity
@NamedNativeQueries ({
    @NamedNativeQuery(name="Techinv.deleteByOrgId",
            query="DELETE FROM techinv where org_id = ?")
})
@NamedQueries ({
    @NamedQuery(name="Techinv.removeUser",
            query="UPDATE Techinv t SET user_id = 0 where t.id = :techid"),
    @NamedQuery(name="Techinv.getAllByOrg",
            query="SELECT p FROM Techinv p where p.organization.liferayId = :orgid"),
    @NamedQuery(name="Techinv.getById",
            query="SELECT t FROM Techinv t where t.id = :id"),
    @NamedQuery(name="Techinv.getByProdOrg",
            query="SELECT p FROM Techinv p where p.organization.liferayId = :orgid and p.product.id = :prodid"),
    @NamedQuery(name="Techinv.delete",
            query="DELETE FROM Techinv t where t.id = :id")
    })
@Table(name="techinv")
public class Techinv implements Serializable {
    private static final long serialVersionUID = 1L;

    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    private int id;

    @Column(name="mu_mask")
    private long muMask;

    @Column(name="mu_assigned_mask")
    private long muAssignedMask;

    @Column(name="mu_asked_assign_mask")
    private long muAskedAssignedMask;

    @Column(name="mu_cert_mask")
    private long muWillCertMask;

    @Column(name="mu_ask_will_cert_mask")
    private long muAskedWillCertMask;

    @Column(name="certType")
    private String certType;

    @Temporal(TemporalType.DATE)
    @Column(name="Apply_date")
    private Date applyDate;

    @Temporal(TemporalType.DATE)
    @Column(name="Cert_date")
    private Date certDate;

    @Lob()
    private String notes;

    //bi-directional many-to-one association to OrgUser
    @ManyToOne
    @JoinColumn(name="user_id")
    private OrgUser orgUser;

    //bi-directional many-to-one association to Organization
    @ManyToOne
    @JoinColumn(name="org_id")
    private Organization organization;

    //bi-directional many-to-one association to Product
    @ManyToOne
    @JoinColumn(name="prod_id")
    private Product product;

    //bi-directional many-to-one association to Certification
    @ManyToOne
    @JoinColumn(name="cert_id")
    private Certification certification;

    public void setCertification(Certification certification) {
        this.certification = certification;
    }

    public Product getProduct() {
        return product;
    }

    public void setProduct(Product product) {
        this.product = product;
    }

    public Techinv() {
    }

    public int getId() {
        return this.id;
    }

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

    public String getNotes() {
        return this.notes;
    }

    public void setNotes(String notes) {
        this.notes = notes;
    }

    public OrgUser getOrgUser() {
        return this.orgUser;
    }

    public void setOrgUser(OrgUser orgUser) {
        this.orgUser = orgUser;
    }

    public Organization getOrganization() {
        return this.organization;
    }

    public void setOrganization(Organization organization) {
        this.organization = organization;
    }

    public long getMuMask() {
        return muMask;
    }

    public void setMuMask(long muMask) {
        this.muMask = muMask;
    }

    public long getMuAssignedMask() {
        return muAssignedMask;
    }

    public void setMuAssignedMask(long muAssigned) {
        this.muAssignedMask = muAssigned;
    }

    public Certification getCertification() {
        return certification;
    }

    public long getMuWillCertMask() {
        return muWillCertMask;
    }

    public void setMuWillCertMask(long muWillCertMask) {
        this.muWillCertMask = muWillCertMask;
    }

    public long getMuAskWillCertMask() {
        return muAskedWillCertMask;
    }

    public void setMuAskedWillCertMask(long muAskedWillCertMask) {
        this.muAskedWillCertMask = muAskedWillCertMask;
    }

    /**
     * This will set the question to true. Once asked and answered, this cannot be unset.
     * @param mu
     */
    public void setMuAskedAssignedMask(Mu mu) {
        this.muAskedAssignedMask |= mu.getMask();
    }

    public boolean isCertified(Mu mu) {
        return getCertification() != null && (getCertification().getMuMask() & mu.getMask()) > 0;
    }

    public boolean isAssigned(Mu mu) {
        return (getMuAssignedMask() & mu.getMask()) > 0;
    }

    public boolean hasAskedToCertify(Mu mu) {
        return isAssigned(mu) && !isCertified(mu) && (getMuAskWillCertMask() & mu.getMask()) > 0;
    }

    public boolean isWillCertify(Mu mu) {
        return hasAskedToCertify(mu) && (getMuWillCertMask() & mu.getMask()) > 0;
    }

    public boolean hasMu(Mu mu) {
        return (getMuMask() & mu.getMask()) > 0;
    }

    public boolean hasAskedToAssign(Mu mu) {
        return (muAskedAssignedMask & mu.getMask()) > 0;
    }

    public String getCertType() {
        return certType;
    }

    public void setCertType(String certType) {
        this.certType = certType;
    }

    public Date getApplyDate() {
        return applyDate;
    }

    public void setApplyDate(Date applyDate) {
        this.applyDate = applyDate;
    }

    public Date getCertDate() {
        return certDate;
    }

    public void setCertDate(Date certDate) {
        this.certDate = certDate;
    }
}

Answer 1

您应检查序列化类中的循环引用，并标记相应的属性@Transient。如果您需要帮助，请发布您的TechModel课程。

编辑：因为使用@Transient不是你的选择，所以使用Gson的@Expose。来自GSON user guide：

此功能提供了一种标记您的某些字段的方法要排除的对象以考虑序列化和反序列化为JSON。要使用此批注，您必须创建Gson 通过使用新的 GsonBuilder（）。excludeFieldsWithoutExposeAnnotation（）。创建（）。该创建的Gson实例将排除类中没有的所有字段用@Expose注释标记。

Answer 2

Type listType = new TypeToken<ArrayList<Techinv>>() {}.getType();

Answer 3

您可以尝试Java API for JSON processing的J2EE的标准实现。

我无法访问您的bean OrgUser，Organization，Product和Certification。所以我假设每个人都包含id和name。

适用于您的List<Techinv> techList。

final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");

List<Techinv> techList = new ArrayList<Techinv>();
for (int i = 1; i <= 3; i++) {
    Techinv tech = new Techinv(i, 1L, 2L, 3L, 4L, 5L, "cert",
            new Date(), new Date(), "notes", new OrgUser(i, "orguser"),
            new Organization(i, "organization"), new Product(i,
                    "product"), new Certification(i, "certification"));
    techList.add(tech);
}
Techinv[] techArr = techList.toArray(new Techinv[techList.size()]);

JsonArrayBuilder techArrBuilder = Json.createArrayBuilder();
for (Techinv tech : techArr) {
    JsonObjectBuilder jsonObject = Json.createObjectBuilder()
        .add("id", tech.getId())
        .add("muMask", tech.getMuMask())
        .add("muAssignedMask", tech.getMuAssignedMask())
        .add("muAskedAssignedMask", tech.getMuAskedAssignedMask())
        .add("muWillCertMask", tech.getMuWillCertMask())
        .add("muAskedWillCertMask", tech.getMuAskedWillCertMask())
        .add("certType", tech.getCertType())
        .add("applyDate", sdf.format(tech.getApplyDate()))
        .add("certDate", sdf.format(tech.getCertDate()))
        .add("notes", tech.getNotes())

        .add("OrgUser", Json.createObjectBuilder()
        .add("id", tech.getOrgUser().getId())
        .add("name", tech.getOrgUser().getName()))

        .add("Organization", Json.createObjectBuilder()
        .add("id", tech.getOrganization().getId())
        .add("name", tech.getOrganization().getName()))

        .add("Product", Json.createObjectBuilder()
        .add("id", tech.getProduct().getId())
        .add("name", tech.getProduct().getName()))

        .add("Certification", Json.createObjectBuilder()
        .add("id", tech.getCertification().getId())
        .add("name", tech.getCertification().getName()));
    techArrBuilder.add(jsonObject);
}
JsonArray jsonArray = techArrBuilder.build();

Map<String, Object> prop = new HashMap<String, Object>() {
    {
        put(JsonGenerator.PRETTY_PRINTING, true);
    }
};
JsonWriter jsonWriter = Json.createWriterFactory(prop).createWriter(System.out);
jsonWriter.writeArray(jsonArray);
jsonWriter.close();

输出应为：

[
    {
        "id":1,
        "muMask":1,
        "muAssignedMask":2,
        "muAskedAssignedMask":3,
        "muWillCertMask":4,
        "muAskedWillCertMask":5,
        "certType":"cert",
        "applyDate":"2014-04-03",
        "certDate":"2014-04-03",
        "notes":"notes",
        "OrgUser":{
            "id":1,
            "name":"orguser"
        },
        "Organization":{
            "id":1,
            "name":"organization"
        },
        "Product":{
            "id":1,
            "name":"product"
        },
        "Certification":{
            "id":1,
            "name":"certification"
        }
    },
    {
        "id":2,
        "muMask":1,
        "muAssignedMask":2,
        "muAskedAssignedMask":3,
        "muWillCertMask":4,
        "muAskedWillCertMask":5,
        "certType":"cert",
        "applyDate":"2014-04-03",
        "certDate":"2014-04-03",
        "notes":"notes",
        "OrgUser":{
            "id":2,
            "name":"orguser"
        },
        "Organization":{
            "id":2,
            "name":"organization"
        },
        "Product":{
            "id":2,
            "name":"product"
        },
        "Certification":{
            "id":2,
            "name":"certification"
        }
    },
    {
        "id":3,
        "muMask":1,
        "muAssignedMask":2,
        "muAskedAssignedMask":3,
        "muWillCertMask":4,
        "muAskedWillCertMask":5,
        "certType":"cert",
        "applyDate":"2014-04-03",
        "certDate":"2014-04-03",
        "notes":"notes",
        "OrgUser":{
            "id":3,
            "name":"orguser"
        },
        "Organization":{
            "id":3,
            "name":"organization"
        },
        "Product":{
            "id":3,
            "name":"product"
        },
        "Certification":{
            "id":3,
            "name":"certification"
        }
    }
]

使用GSON的JSON Java对象会产生stackoverflow错误

第一次尝试

第二次尝试

第3次尝试

Techinv课程（如果需要）

3 个答案: