Apachce tomcat / 7.0.30下载文件时出现Http状态404错误

Question

我尝试使用JSF下载文件，方法是在运行程序时将表属性作为路径，它运行正常一次，然后错误来到HTTP状态404 ...我该怎么做才能下载文件？

XHTML代码

<p:dataTable id="idAttachmentTable" var="attach"
             value="#{documentMB.attachList1}"
             selectionMode="single"
             selection="#{documentMB.selectedAttachment}"
             rowKey="#{attach.attachmentId}">

    <f:facet name="header">
        Attachments
    </f:facet>

    <p:column headerText="#{bundle.subject}">
        <h:outputText value="#{attach.attachName}" />

    </p:column>

    <p:column>
        <h:commandLink id="getDownload" value="#{attach.attachName}" action="#{documentMB.downLoad}">
            <f:setPropertyActionListener target="#{documentMB.selectedAttachment}" value="#{attach}" />
        </h:commandLink>
    </p:column>
</p:dataTable>

documentMb.java

private static final int DEFAULT_BUFFER_SIZE = 10240;
private String filePath = "C:\\temp\\123.PNG";

public void downLoad() throws IOException {
    System.out.println("in download");
    FacesContext context = FacesContext.getCurrentInstance();
    HttpServletResponse response = (HttpServletResponse) context.getExternalContext().getResponse();

    System.out.println("after Faces");
    System.out.println(filePath);
    System.out.println(selectedAttachment.getAttachmentName());

    java.io.File file = new java.io.File(selectedAttachment.getAttachmentName());
    System.out.println(selectedAttachment.getAttachmentName());

    if (!file.exists()) {
        System.out.println(selectedAttachment.getAttachmentName());
        response.sendError(HttpServletResponse.SC_NOT_FOUND);
        return;
    }

    response.reset();
    response.setBufferSize(DEFAULT_BUFFER_SIZE);
    response.setContentType("application/octet-stream");
    response.setHeader("Content-Length", String.valueOf(file.length()));
    response.setHeader("Content-Disposition", "attachment;filename=\"" + file.getName() + "\"");
    System.out.println(file.getName());
    BufferedInputStream input = null;
    BufferedOutputStream output = null;

    try {
        input = new BufferedInputStream(new FileInputStream(file), DEFAULT_BUFFER_SIZE);
        output = new BufferedOutputStream(response.getOutputStream(), DEFAULT_BUFFER_SIZE);
        byte[] buffer = new byte[DEFAULT_BUFFER_SIZE];
        int length;

        while ((length = input.read(buffer)) > 0) {
            output.write(buffer, 0, length);
        }

    } finally {
        input.close();
        output.close();
    }
    context.responseComplete();
}