spring-mvc - Thymeleaf，Spring MVC 表单提交时缺少表单支持对象 : null

Question

基本上，表单提交中的表单支持对象始终为 null。谁能明白为什么会这样吗？

我有一个简单的 Controller ，可以显示设备列表。可以选择设备并向其应用功能。这是 Controller :

@Controller
@RequestMapping
public class DeviceListController {

    private static final Logger LOG = LoggerFactory.getLogger(DeviceListController.class);

    @Autowired
        DeviceService deviceService;

    @RequestMapping("/devices/list")
    public String getDevicesPage(ModelMap model) {
        int page = 0;
        int size = 10;

        if(model.get("deviceCommand") != null) {
            DeviceCommand cmd = (DeviceCommand) model.get("deviceCommand");
            page = cmd.getPage();
            size = cmd.getSize();
        }
        Pageable pageRequest = new PageRequest(page, size);
        Page<Device> devices = deviceService.findAllPaginated(pageRequest);

        model.addAttribute("devices", DeviceMapper.map(devices));
        model.addAttribute("deviceCommand", new DeviceCommand(page, size));
        return "devices";
    }

    @RequestMapping("/devices/modify")
    public String modifyDevices(ModelMap model) {

        LOG.debug("Trying to get the device command {}.", model.get("deviceCommand"));

        if(model.get("deviceCommand") != null) {
            DeviceCommand cmd = (DeviceCommand) model.get("deviceCommand");

            LOG.debug("Processing directives {} and {} for {}.", cmd.getNewVersion(),cmd.getNewCommand(),cmd.getDeviceModificationIds());

        }
        return getDevicesPage(model);
    }
}

设备模型对象是一个休眠实体:

@Entity //TODO:  no connection between device and device details!
@Table(name="device")
public class Device {
    @Id
    @GeneratedValue
    private Long id;

    /**
     * This is an external representation of the device, and the ID for which the device is most
     * commonly searched for. The deviceID is a common reference point, used in T2 and in device reporting
     * on the client side.
     */
    @Column(name="device_id")
    private String deviceId;

    /**
     * A reference to the store number or store identification. Stores may have more than one device.
     */
    @Column(name="retailer_id")
    private String retailerId;

    /**
     * The name of the store where the device is situated.
     */
    @Column(name="retailer_name")
    private String retailerName;

    /**
     * The current version of the client software, which launches the browser. This is only applicable to integrated solutions
     */
    @Column(name="current_client_version")
    private String currentClientVersion;

    /**
     * The target version of the client software, which launches the browser. This is only applicable to integrated solutions
     */
    @Column(name="next_client_version")
    private String nextClientVersion;

    /**
     * Commands to be performed on the client, used most often to "clear the cache". As soon as hte se commands are run, they
     * are cleared from this column.
     */
    @Column(name="commands")
    private String commands;


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

    /**
     * The signature is the client's position in the marketplace and used by other entities
     * to determine their applicability to the device.
     * RETAILER_GROUP:Tobaccoland|CHANNEL:Logistik|LOCALE:de-AT|INDUSTRY:5499
     * The * notation means any, the locale is using the standard locale code (up to 10 characters)
     * and the industry uses the merchant category codes, which in this case is
     * Miscellaneous Food Stores - Convenience Stores and Specialty Markets
     */
    @Column(name = "signature")
    private String signature;  //TODO: normalise?

    /**
     * This is the traceId that the device is currently up to
     */
    @Column(name = "trace_id")
    private Long traceId;
    /**
     * This is a tracing number that will be generated by touchpoint on each request.
     */
    @Column(name = "last_trace_id")
    private Long lastTraceId;

    /**
     * This is the transaction number that will come from Mercury in each response.
     */
    @Column(name = "last_transaction_id")
    private Long lastTransactionId;

    @ManyToMany(cascade=CascadeType.ALL)
    @JoinTable(name="device_role",
        joinColumns = {@JoinColumn(name="device_id", referencedColumnName="id")},
        inverseJoinColumns = {@JoinColumn(name="role_id", referencedColumnName="id")}
    )
    private List<Role> roles;

    @ManyToMany(cascade= CascadeType.ALL, mappedBy = "devices", fetch = FetchType.LAZY)
    private Set<User> users;

    // getters, setters, equals, hashcode, omitted
}

并通过 DeviceMapper 映射到 DeviceViewModel

DeviceViewModel:

public class DeviceViewModel {

    private String id;
    private String retailerName;
    private String currentClientVersion;
    private String nextClientVersion;
    private String commands;
    private boolean shallModify;

    public String getId() {
        return id;
    }

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

    public String getRetailerName() {
        return retailerName;
    }

    public void setRetailerName(String retailerName) {
        this.retailerName = retailerName;
    }

    public String getCurrentClientVersion() {
        return currentClientVersion;
    }

    public void setCurrentClientVersion(String currentClientVersion) {
        this.currentClientVersion = currentClientVersion;
    }

    public String getNextClientVersion() {
        return nextClientVersion;
    }

    public void setNextClientVersion(String nextClientVersion) {
        this.nextClientVersion = nextClientVersion;
    }

    public String getCommands() {
        return commands;
    }

    public void setCommands(String commands) {
        this.commands = commands;
    }

    public boolean isShallModify() {
        return shallModify;
    }

    public void setShallModify(boolean shallModify) {
        this.shallModify = shallModify;
    }
}

和DeviceMapper:

public class DeviceMapper {

    public static DeviceViewModel map(Device device) {
        DeviceViewModel dto = new DeviceViewModel( );
        dto.setId( device.getDeviceId() );
        dto.setRetailerName( device.getRetailerName() );
        dto.setCurrentClientVersion( device.getCurrentClientVersion() );
        dto.setNextClientVersion( device.getNextClientVersion() );
        dto.setCommands( device.getCommands() );
        return dto;
    }

    public static List<DeviceViewModel> map(Page<Device> devices) {
        List<DeviceViewModel> dtos = new ArrayList<>();

        for(Device device : devices) {
            dtos.add( map( device ) );
        }

        return dtos;
    }
}

现在是 DeviceCommand，它是我的表单支持对象:

public class DeviceCommand {

    private List<String> deviceModificationIds;
    private String newVersion;
    private String newCommand;
    private int page;
    private int size;

    public DeviceCommand() {}

    public DeviceCommand(int page, int size) {
        this.page = page;
        this.size = size;
    }

    public List<String> getDeviceModificationIds() {
        return deviceModificationIds;
    }

    public void setDeviceModificationIds(List<String> deviceModificationIds) {
        this.deviceModificationIds = deviceModificationIds;
    }

    public String getNewVersion() {
        return newVersion;
    }

    public void setNewVersion(String newVersion) {
        this.newVersion = newVersion;
    }

    public String getNewCommand() {
        return newCommand;
    }

    public void setNewCommand(String newCommand) {
        this.newCommand = newCommand;
    }

    public int getPage() {
        return page;
    }

    public void setPage(int page) {
        this.page = page;
    }

    public int getSize() {
        return size;
    }

    public void setSize(int size) {
        this.size = size;
    }
}

最后是 devices.html 页面的相关部分:

<form action="#" th:action="@{/devices/modify}" th:object="${deviceCommand}" method="post">
<table class="box-table-a">
    <h1 th:text="#{device.table.caption}">Site Users</h1>
    <thead>
        <tr>
            <th scope="col" th:text="#{device.check.label}">Select</th>
            <th scope="col" th:text="#{device.id.label}">(<span th:text="${device.retailer.name.label}"></span>)</th>
            <th scope="col" th:text="#{device.current.label}">Curr Version</th>
            <th scope="col" th:text="#{device.next.label}">Next Version</th>
            <th scope="col" th:text="#{device.commands.label}">Commands</th>
        </tr>
    </thead>
    <tbody>
        <tr th:each="d : ${devices}">
            <td><input type="checkbox" th:field="*{deviceModificationIds}" th:value="${d.id}"/></td>
            <td th:text="${d.id}">(<span th:text="${d.retailerName}"></span>)</td>
            <td th:text="${d.currentClientVersion}">Washington</td>
            <td th:text="${d.nextClientVersion}">gwash</td>
            <td th:text="${d.commands}">gwash</td>
        </tr>
        <tr>
        <td colspan="2">

            </td>
            <td th:text="#{device.change.version.label}"></td>
            <td th:text="#{device.add.command.label}"></td>
            <td></td>
        </tr>
        <tr>
        <td colspan="2">

            </td>
            <td><input type="text" th:field="*{newVersion}"/></td>
            <td><input type="text" th:field="*{newCommand}"/></td>
            <td><button type="submit" th:text="#{device.modify.action.button}">Action</button></td>
        </tr>
    </tbody>
</table>
</form>

虽然表单操作确实到达了 Controller 中的modifyDevices方法，但deviceCommand表单支持对象为空。

为什么会这样？

Answer 1

只需将 DeviceViewModel 类型的参数添加到您的 modifyDevices 方法
所以会是这样的

@RequestMapping("/devices/modify")
public String modifyDevices(ModelMap model, DeviceViewModel deviceCommand ) {
/* access the submitted object as you want ....*/
}

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