getAsString（）jsf customed转换器无法转换对象

Question

我为jsf创建了一个自定义转换器。 getAsObject（）工作正常，但getAsString（）返回异常。我不确定问题出在哪里，我已经尝试以不同的方式将对象转换为字符串，但它一直在返回异常。

这是我的转换器代码：

    @Named
public class ProductConverter implements Converter{

    @EJB
    private ProductEJB productEjb;

    @Override
    public Object getAsObject(FacesContext context, UIComponent component, String value) {
        if(value== null )
        {
            throw new ConverterException("There was an error at getAsObject()");
        }

        int id = Integer.parseInt(value);
        return productEjb.findProductById(id);
    }

    @Override    
    public String getAsString(FacesContext context, UIComponent component, Object value) {        

        if (value == null || value.equals("")) 
        {
            return "";            
        }
        else
        {
            Integer id = ((Product)value).getProduct_id();
            return String.valueOf(id);
        }

    }

}

这是Product类（为简单起见，排除了Getters / Setters / equals（）/ hash（））：

@Entity
@NamedQueries({
    @NamedQuery(name="findAllProducts", query = "SELECT p from Product p")

})
public class Product implements Serializable
{
    private static final long serialVersionUID = 1L;

    @Id @GeneratedValue(strategy= GenerationType.AUTO)
    private int product_id;
    private String name;
    private String description;
    protected byte[] imageFile;
    private Float price;
    @Temporal(TemporalType.TIMESTAMP)
    private Date dateAdded;        
    @ManyToOne
    private Category category_fk;
    @ManyToOne
    private SaleDetails saleDetails_fk;

这是我得到的堆栈：

java.lang.NumberFormatException: For input string: ""
    at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
    at java.lang.Integer.parseInt(Integer.java:504)
    at java.lang.Integer.parseInt(Integer.java:527)
    at com.lv.Controllers.Converters.ProductConverter.getAsObject(ProductConverter.java:30)
    at com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getConvertedValue(HtmlBasicInputRenderer.java:171)
    at javax.faces.component.UIViewParameter.getConvertedValue(UIViewParameter.java:394)
    at javax.faces.component.UIInput.validate(UIInput.java:960)
    at javax.faces.component.UIInput.executeValidate(UIInput.java:1233)
    at javax.faces.component.UIInput.processValidators(UIInput.java:698)
    at javax.faces.component.UIViewParameter.processValidators(UIViewParameter.java:273)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1214)
    at javax.faces.component.UIComponentBase.processValidators(UIComponentBase.java:1214)
    at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:1172)
    at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:76)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1550)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
    at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:860)
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:757)
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1056)
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:229)
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
    at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
    at java.lang.Thread.run(Thread.java:722)

这是我使用转换器的jsf：

<f:metadata>
    <f:viewParam name="product" value="#{productDelete.product}" converter="#{productConverter}"/>
</f:metadata>

Answer 1

当收到null或空值时，不要抛出异常。这毫无意义。它们可能代表合法有效的值，只代表“无价值”。然后返回null。如果您想强制要求，那么您应该使用required="true"或任何自定义Validator，但不要在Converter中执行此操作。

只有当值真正不可转换时，才应抛出ConverterException。我已经改进了你的转换器来做到这一点。您不是检查提交的值是否为有效数字，也不是检查获得的模型值是Product的实例。否则会导致NumberFormatException或ClassCastException进一步降低代码，您应该通过抛出适当的ConverterException来预防。

@Named
public class ProductConverter implements Converter {

    @EJB
    private ProductEJB productEjb;

    @Override
    public Object getAsObject(FacesContext context, UIComponent component, String value) {
        if (value == null || value.isEmpty()) {
            return null;
        }

        if (!value.matches("\\d+")) {
            throw new ConverterException("The value is not a valid ID number: " + value);
        }

        int id = Integer.parseInt(value);
        return productEjb.findProductById(id);
        // You may want to perform an additional check if it didn't return null
        // and otherwise throw ConverterException with "unknown Product ID".
    }

    @Override    
    public String getAsString(FacesContext context, UIComponent component, Object value) {        
        if (value == null) {
            return null; // Or an empty string, can also.
        }

        if (!(value instanceof Product)) {
            throw new ConverterException("The value is not a valid Product: " + value);
        }

        Integer id = ((Product)value).getProduct_id();
        return (id != null) ? String.valueOf(id) : null;
    }

}

Answer 2

当值为null时，看起来您的方法无法处理。在这种情况下尝试返回一个空字符串

public String getAsString(FacesContext facesContext, UIComponent component, Object value) {
    if (value == null || value.equals("")) {
        return "";
    } else {
        Integer id = ((Product)value).getProduct_id();
        return String.valueOf(id);
    }
}

Answer 3

值表达式#{productDelete.product}正在解析为null。

注意：转换器的contract表明getAsString为空值返回空字符串。