p:selectManyMenu 和@FacesConverter(forClass = Clazz.class)

Question

<p:selectManyMenu id="colourList"
                  var="color"
                  value="#{testBean.selectedColours}"
                  converter="#{colourConverter}"
                  showCheckbox="true"
                  required="true"
                  label="Colour"
                  style="overflow: auto; width: 317px; background-color: white; max-height: 200px;">

    <f:selectItems var="colour"
                   value="#{testBean.colours}"
                   itemLabel="#{colour.colourHex}"
                   itemValue="#{colour}"/>
    <p:column>
        <span style="display: inline-block; width: 275px; height: 20px; background-color:\##{color.colourHex}; border: 1px solid black;"
              title="Name: #{color.colourName} | Hex: #{color.colourHex}" />
    </p:column>
</p:selectManyMenu>

<p:commandButton value="Submit" actionListener="#{testBean.action}"/>

_{CSS原封不动，如果有人想把这个例子付诸实践的话。它将显示三种基本颜色 (RGB)，前面有复选框，如下所示。}

托管 bean：

@Named
@ViewScoped
public class TestBean implements Serializable {

    @Inject
    private DataStore dataStore;
    private List<Colour> colours; //Getter & setter.
    private List<Colour> selectedColours; //Getter & setter.
    private static final long serialVersionUID = 1L;

    public TestBean() {}

    @PostConstruct
    private void init() {
        colours = dataStore.getColours();
    }

    public void action() {
        for (Colour colour : selectedColours) {
            System.out.println("colourName : "
                    + colour.getColourName()
                    + " : colourHex : "
                    + colour.getColourHex());
        }
    }
}

如果从 <p:selectManyMenu> 中删除 converter="#{colourConverter}" 属性，那么它会导致 java.lang.ClassCastException 在 action() 方法中抛出，即使转换器用 @FacesConverter(forClass = Colour.class).

java.lang.ClassCastException: java.lang.String cannot be cast to com.example.Colour

看来是泛型橡皮擦问题（List<Colour>的泛型类型参数在运行时被去掉，变成无类型的List）。

Colour[] 应该可以工作，但是在尝试时 action() 方法本身没有被调用。

它需要明确提及转换器的确切原因是什么？

补充：

转换器：

@Named
@ApplicationScoped
@FacesConverter(forClass = Colour.class)
public class ColourConverter implements Converter {

    @Inject
    private DataStore dataStore;

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

        try {
            long parsedValue = Long.parseLong(value);

            if (parsedValue <= 0) {
                throw new ConverterException("FacesMessage");
            }

            Colour entity = dataStore.findColourById(parsedValue);

            if (entity == null) {
                throw new ConverterException("FacesMessage");
            }
            return entity;
        } catch (NumberFormatException e) {
            throw new ConverterException("FacesMessage", e);
        }
    }

    @Override
    public String getAsString(FacesContext context, UIComponent component, Object value) {
        if (value == null) {
            return "";
        }

        if (!(value instanceof Colour)) {
            throw new ConverterException("Message");
        }

        Long id = ((Colour) value).getColourId();
        return id != null ? id.toString() : "";
    }
}

维护 List<Colour> 的应用程序范围 bean。

@Named
@ApplicationScoped
public class DataStore {

    private List<Colour> colours;

    public DataStore() {}

    @PostConstruct
    private void init() {
        colours = new ArrayList<>();

        Colour colour = new Colour();
        colour.setColourId(1L);
        colour.setColourName("Red");
        colour.setColourHex("FF0000");
        colours.add(colour);

        colour = new Colour();
        colour.setColourId(3L);
        colour.setColourName("Green");
        colour.setColourHex("008000");
        colours.add(colour);

        colour = new Colour();
        colour.setColourId(2L);
        colour.setColourName("Blue");
        colour.setColourHex("0000FF");
        colours.add(colour);
    }

    public Colour findColourById(Long id) {
        for (Colour colour : colours) {
            if (colour.getColourId().equals(id)) {
                return colour;
            }
        }

        return null;
    }

    public List<Colour> getColours() {
        return colours;
    }
}

领域模型class：

public class Colour implements Serializable {

    private Long colourId;
    private String colourName;
    private String colourHex;
    private static final long serialVersionUID = 1L;

    public Colour() {}

    public Long getColourId() {
        return colourId;
    }

    public void setColourId(Long colourId) {
        this.colourId = colourId;
    }

    public String getColourName() {
        return colourName;
    }

    public void setColourName(String colourName) {
        this.colourName = colourName;
    }

    public String getColourHex() {
        return colourHex;
    }

    public void setColourHex(String colourHex) {
        this.colourHex = colourHex;
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 47 * hash + Objects.hashCode(getColourId());
        return hash;
    }

    @Override
    public boolean equals(Object that) {
        if (!(that instanceof Colour)) {
            return false;
        }

        return this == that || Objects.equals(getColourId(), ((Colour) that).getColourId());
    }

    @Override
    public String toString() {
        return String.format("%s[colourId=%d]", getClass().getCanonicalName(), getColourId());
    }
}

Answer 1

这个问题有两个方面。

第一个问题是EL无法确定模型值类型，因为泛型类型信息在运行时会丢失。基本上变成了Object.class。您基本上需要将 List<Colour> 替换为 Colour[]。这个问题详细回答了这个问题：UISelectMany on a List<T> causes java.lang.ClassCastException: java.lang.String cannot be cast to T.

第二个问题是 PrimeFaces InputRenderer 有一个错误，它在定位转换器之前没有考虑数组类型。下面的行号匹配 5.2

156    protected Converter findImplicitConverter(FacesContext context, UIComponent component) {
157        ValueExpression ve = component.getValueExpression("value");
158
159        if(ve != null) {
160            Class<?> valueType = ve.getType(context.getELContext());
161                
162            if(valueType != null)
163                return context.getApplication().createConverter(valueType);
164        }
165
166        return null;
167    }

在您的特定情况下，valueType 是 Colour[].class 而不是 Colour.class。这解释了为什么它无法找到与 Colour.class 关联的转换器。在创建转换器之前，它应该检查 valueType 是否是来自它的 array type and if so then extract the component type。

if (valueType.isArray()) {
    valueType = valueType.getComponentType();
}

你最好将此作为错误报告给 PrimeFaces 人员，同时说明它在 <h:selectManyMenu> 等标准组件中运行良好。同时，最好的办法是明确注册转换器。

p:selectManyMenu 和@FacesConverter(forClass = Clazz.class)

p:selectManyMenu and @FacesConverter(forClass = Clazz.class)

jsf

converter

primefaces

selectmanymenu