在jsf页面中使用commandButton下载文件

<h:form>
    <h:commandButton value="下载文件" action="#{bean.downloadFile}" />
</h:form>

import javax.faces.context.FacesContext;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;

public class Bean {
    public void downloadFile() throws IOException {
        // 获取FacesContext和HttpServletResponse对象
        FacesContext facesContext = FacesContext.getCurrentInstance();
        HttpServletResponse response = (HttpServletResponse) facesContext.getExternalContext().getResponse();

        // 设置响应头信息
        response.setContentType("application/octet-stream");
        response.setHeader("Content-Disposition", "attachment;filename=filename.ext");

        // 读取文件并写入响应流
        File file = new File("path/to/file");
        FileInputStream fileInputStream = new FileInputStream(file);
        OutputStream outputStream = response.getOutputStream();
        byte[] buffer = new byte[4096];
        int length;
        while ((length = fileInputStream.read(buffer)) > 0) {
            outputStream.write(buffer, 0, length);
        }
        outputStream.flush();

        // 关闭流
        fileInputStream.close();
        outputStream.close();

        // 结束JSF生命周期
        facesContext.responseComplete();
    }
}

<navigation-rule>
    <from-view-id>/jsf-page.xhtml</from-view-id>
    <navigation-case>
        <from-outcome>download</from-outcome>
        <to-view-id>/jsf-page.xhtml</to-view-id>
        <redirect />
    </navigation-case>
</navigation-rule>