Using java.util.Map in h:dataTable

问题

I need to display Map using <h:dataTable>. My backing bean has a Map property as below:

public class Bean {

    private Map<Integer,String> map; // +getter

    @PostConstruct
    public void init() {
        map = new TreeMap<Integer,String>();
        map.put(1,\"Sasi\");
        map.put(2,\"Pushparaju\");
        map.put(3,\"Venkat Raman\");
        map.put(3,\"Prabhakaran\");
    }

}

Then in JSF page I am trying to bind this Map property to the value attribute of <h:dataTable>.

 <h:dataTable border=\"1\" value=\"#{bean.map}\" var=\"map\">
    <h:column id=\"column1\">
        <f:facet name=\"header\">
            <h:outputText value=\"UserId\"></h:outputText>
        </f:facet>
        <h:outputText value=\"#{map.getKey}\"></h:outputText>
    </h:column>
    <h:column id=\"column2\">
        <f:facet name=\"header\">
            <h:outputText value=\"Email Id\"></h:outputText>
        </f:facet>
        <h:outputText value=\"#{map.getValue}\"></h:outputText>
    </h:column>
</h:dataTable>

It is giving en error that getKey and getValue is not present. I can understand that this is not the correct way to do it. How can I present a Map using <h:dataTable>?

回答1:

Until upcoming JSF 2.3, UIData components such as <h:dataTable>, <p:dataTable>, etc and <ui:repeat> does not support iterating over a Map. This is only supported in <c:forEach>.

One way is to convert the map entries to an array (alone entrySet() won't work as UIData also doesn't support Set until upcoming JSF 2.3).

<h:dataTable value="#{bean.map.entrySet().toArray()}" var="entry">
    <h:column>#{entry.key}</h:column>
    <h:column>#{entry.value}</h:column>
</h:dataTable>

Another way is to wrap the map's entry set in a collection which the <h:dataTable> can iterate over, such as an ArrayList.

public class Bean {

    private Map<Integer, String> map;
    private List<Entry<Integer, String>> entries; // +getter (no setter necessary)

    @PostConstruct
    public void init() {
        map = new TreeMap<>();
        map.put(1, "Sasi");
        map.put(2, "Pushparaju");
        map.put(3, "Venkat Raman");
        map.put(4, "Prabhakaran");
        entries = new ArrayList<>(map.entrySet());
    }

    // ...
}

<h:dataTable value="#{bean.entries}" var="entry">
    <h:column>#{entry.key}</h:column>
    <h:column>#{entry.value}</h:column>
</h:dataTable>

However, more clean, self documenting and reusable is to use a List<User> instead wherein the User class has the necessary properties id and name.

public class Bean {

    private List<User> users; // +getter (no setter necessary)

    @PostConstruct
    public void init() {
        users = new ArrayList<>();
        users.add(new User(1, "Sasi"));
        users.add(new User(2, "Pushparaju"));
        users.add(new User(3, "Venkat Raman"));
        users.add(new User(4, "Prabhakaran"));
    }

    // ...
}

<h:dataTable value="#{bean.users}" var="user">
    <h:column>#{user.id}</h:column>
    <h:column>#{user.name}</h:column>
</h:dataTable>

回答2:

You can try this alternative too.

<h:dataTable border="1" value="#{myBean.map.keySet().toArray()}" var="myVar">
    <h:column id="column1">
        <f:facet name="header">
            <h:outputText value="UserId"></h:outputText>
        </f:facet>
            <h:outputText value="#{myVar}"></h:outputText>
    </h:column>
    <h:column id="column2">
        <f:facet name="header">
            <h:outputText value="Email Id"></h:outputText>
        </f:facet>
            <h:outputText value="#{myBean.map.get(myVar)}"></h:outputText>
    </h:column>
</h:dataTable>

回答3:

Regarding to the last answer from prageeth, you may use entrySet instead of keySet; then you can get rid of myBean.map.get. See this example:

<h:dataTable border="1" value="#{myBean.map.entrySet().toArray()}" var="map">
<h:column id="column1">
    <f:facet name="header">
        <h:outputText value="UserId"></h:outputText>
    </f:facet>
        <h:outputText value="#{map.key}"></h:outputText>
</h:column>
<h:column id="column2">
    <f:facet name="header">
        <h:outputText value="Email Id"></h:outputText>
    </f:facet>
        <h:outputText value="#{map.value}"></h:outputText>
</h:column>
</h:dataTable>

This works on myfaces 2.2.3 as I've just used it myself.

Annotation: I'd better had commented the last post, but my reputation is not high enough, therefore this is an extra answer.

来源：https://stackoverflow.com/questions/14343788/using-java-util-map-in-hdatatable

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