本文介绍Servlet 3.0规范中的文件上传功能及异步处理机制，详细讲解了如何利用MultipartConfig注解和Part接口实现文件上传，并展示了如何通过AsyncContext实现异步任务处理。
Upload-上传
随着3.0版本的发布,文件上传终于成为Servlet规范的一项内置特性,不再依赖于像Commons FileUpload之类组件,因此在服务端进行文件上传编程变得不费吹灰之力.
客户端
要上传文件, 必须利用multipart/form-data设置HTML表单的enctype属性,且method必须为POST:
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<form action=
"simple_file_upload_servlet.do"
method=
"POST"
enctype=
"multipart/form-data"
>
<table align=
"center"
border=
"1"
width=
"50%"
>
<tr>
<td>Author:</td>
<td><input type=
"text"
name=
"author"
></td>
</tr>
<tr>
<td>Select file to Upload:</td>
<td><input type=
"file"
name=
"file"
></td>
</tr>
<tr>
<td><input type=
"submit"
value=
"上传"
></td>
</tr>
</table>
</form>
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服务端
服务端Servlet主要围绕着
@MultipartConfig注解和Part接口:
处理上传文件的Servlet必须用@MultipartConfig注解标注:
| @MultipartConfig属性 | 描述 |
|---|---|
fileSizeThreshold | The size threshold after which the file will be written to disk |
location | The directory location where files will be stored |
maxFileSize | The maximum size allowed for uploaded files. |
maxRequestSize | The maximum size allowed for multipart/form-data requests |
在一个由多部件组成的请求中, 每一个表单域(包括非文件域), 都会被封装成一个Part,HttpServletRequest中提供如下两个方法获取封装好的Part:
| HttpServletRequest | 描述 |
|---|---|
Part getPart(String name) | Gets the Part with the given name. |
Collection<Part> getParts() | Gets all the Part components of this request, provided that it is of type multipart/form-data. |
Part中提供了如下常用方法来获取/操作上传的文件/数据:
| Part | 描述 |
|---|---|
InputStream getInputStream() | Gets the content of this part as an InputStream |
void write(String fileName) | A convenience method to write this uploaded item to disk. |
String getSubmittedFileName() | Gets the file name specified by the client(需要有Tomcat 8.x 及以上版本支持) |
long getSize() | Returns the size of this fille. |
void delete() | Deletes the underlying storage for a file item, including deleting any associated temporary disk file. |
String getName() | Gets the name of this part |
String getContentType() | Gets the content type of this part. |
Collection<String> getHeaderNames() | Gets the header names of this Part. |
String getHeader(String name) | Returns the value of the specified mime header as a String. |
文件流解析
通过抓包获取到客户端上传文件的数据格式:
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------WebKitFormBoundaryXJ6TxfJ9PX5hJHGh
Content-Disposition: form-data; name=
"author"
feiqing
------WebKitFormBoundaryXJ6TxfJ9PX5hJHGh
Content-Disposition: form-data; name=
"file"
; filename=
"memcached.txt"
Content-Type: text/plain
------WebKitFormBoundaryXJ6TxfJ9PX5hJHGh--
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-
可以看到:
-
A. 如果HTML表单输入项为文本(
<input type="text"/>),将只包含一个请求头Content-Disposition. -
B. 如果HTML表单输入项为文件(
<input type="file"/>), 则包含两个头:
Content-Disposition与Content-Type.
在Servlet中处理上传文件时, 需要:
<code>- 通过查看是否存在`Content-Type`标头, 检验一个Part是封装的普通表单域,还是文件域. - 若有`Content-Type`存在, 但文件名为空, 则表示没有选择要上传的文件. - 如果有文件存在, 则可以调用`write()`方法来写入磁盘, 调用同时传递一个绝对路径, 或是相对于`@MultipartConfig`注解的`location`属性的相对路径. </code>
- SimpleFileUploadServlet
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/**
* @author jifang.
* @since 2016/5/8 16:27.
*/
@MultipartConfig
@WebServlet
(name =
"SimpleFileUploadServlet"
, urlPatterns =
"/simple_file_upload_servlet.do"
)
public
class
SimpleFileUploadServlet
extends
HttpServlet {
protected
void
doPost(HttpServletRequest request, HttpServletResponse response)
throws
ServletException, IOException {
response.setContentType(
"text/html;charset=UTF-8"
);
PrintWriter writer = response.getWriter();
Part file = request.getPart(
"file"
);
if
(!isFileValid(file)) {
writer.print(
"<h1>请确认上传文件是否正确!"
);
}
else
{
String fileName = file.getSubmittedFileName();
String saveDir = getServletContext().getRealPath(
"/WEB-INF/files/"
);
mkdirs(saveDir);
file.write(saveDir + fileName);
writer.print(
"<h3>Uploaded file name: "
+ fileName);
writer.print(
"<h3>Size: "
+ file.getSize());
writer.print(
"<h3>Author: "
+ request.getParameter(
"author"
));
}
}
private
void
mkdirs(String saveDir) {
File dir =
new
File(saveDir);
if
(!dir.exists()) {
dir.mkdirs();
}
}
private
boolean
isFileValid(Part file) {
// 上传的并非文件
if
(file.getContentType() ==
null
) {
return
false
;
}
// 没有选择任何文件
else
if
(Strings.isNullOrEmpty(file.getSubmittedFileName())) {
return
false
;
}
return
true
;
}
}
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优化
- 善用
WEB-INF
存放在/WEB-INF/目录下的资源无法在浏览器地址栏直接访问, 利用这一特点可将某些受保护资源存放在WEB-INF目录下, 禁止用户直接访问(如用户上传的可执行文件,如JSP等),以防被恶意执行, 造成服务器信息泄露等危险.
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getServletContext().getRealPath(
"/WEB-INF/"
)
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- 文件名乱码
当文件名包含中文时,可能会出现乱码,其解决方案与POST相同:
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1
request.setCharacterEncoding("UTF-8");避免文件同名
如果上传同名文件,会造成文件覆盖.因此可以为每份文件生成一个唯一ID,然后连接原始文件名:
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private
String generateUUID() {
return
UUID.randomUUID().toString().replace(
"-"
,
"_"
);
}
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- 目录打散
如果一个目录下存放的文件过多, 会导致文件检索速度下降,因此需要将文件打散存放到不同目录中, 在此我们采用Hash打散法(根据文件名生成Hash值, 取Hash值的前两个字符作为二级目录名), 将文件分布到一个二级目录中:
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private
String generateTwoLevelDir(String destFileName) {
String hash = Integer.toHexString(destFileName.hashCode());
return
String.format(
"%s/%s"
, hash.charAt(
0
), hash.charAt(
1
));
}
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采用Hash打散的好处是:在根目录下最多生成16个目录,而每个子目录下最多再生成16个子子目录,即一共256个目录,且分布较为均匀.
web全新视频：www.makeru.com.cn/?t=12
示例-简易存储图片服务器
需求: 提供上传图片功能, 为其生成外链, 并提供下载功能(见下)
- 客户端
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<html>
<head>
<meta http-equiv=
"Content-Type"
content=
"text/html; charset=UTF-8"
>
<title>IFS</title>
</head>
<body>
<form action=
"ifs_upload.action"
method=
"POST"
enctype=
"multipart/form-data"
>
<table align=
"center"
border=
"1"
width=
"50%"
>
<tr>
<td>Select A Image to Upload:</td>
<td><input type=
"file"
name=
"image"
></td>
</tr>
<tr>
<td> </td>
<td><input type=
"submit"
value=
"上传"
></td>
</tr>
</table>
</form>
</body>
</html>
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- 服务端
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@MultipartConfig
@WebServlet
(name =
"ImageFileUploadServlet"
, urlPatterns =
"/ifs_upload.action"
)
public
class
ImageFileUploadServlet
extends
HttpServlet {
private
Set<String> imageSuffix =
new
HashSet<>();
private
static
final
String SAVE_ROOT_DIR =
"/images"
;
{
imageSuffix.add(
".jpg"
);
imageSuffix.add(
".png"
);
imageSuffix.add(
".jpeg"
);
}
@Override
protected
void
doPost(HttpServletRequest request, HttpServletResponse response)
throws
ServletException, IOException {
request.setCharacterEncoding(
"UTF-8"
);
response.setContentType(
"text/html;charset=UTF-8"
);
PrintWriter writer = response.getWriter();
Part image = request.getPart(
"image"
);
String fileName = getFileName(image);
if
(isFileValid(image, fileName) && isImageValid(fileName)) {
String destFileName = generateDestFileName(fileName);
String twoLevelDir = generateTwoLevelDir(destFileName);
// 保存文件
String saveDir = String.format(
"%s/%s/"
, getServletContext().getRealPath(SAVE_ROOT_DIR), twoLevelDir);
makeDirs(saveDir);
image.write(saveDir + destFileName);
// 生成外链
String ip = request.getLocalAddr();
int
port = request.getLocalPort();
String path = request.getContextPath();
String urlPrefix = String.format(
"http://%s:%s%s"
, ip, port, path);
String urlSuffix = String.format(
"%s/%s/%s"
, SAVE_ROOT_DIR, twoLevelDir, destFileName);
String url = urlPrefix + urlSuffix;
String result = String.format(
"<a href=%s>%s</a><hr/><a href=ifs_download.action?location=%s>下载</a>"
,
url,
url,
saveDir + destFileName);
writer.print(result);
}
else
{
writer.print(
"Error : Image Type Error"
);
}
}
/**
* 校验文件表单域有效
*
* @param file
* @param fileName
* @return
*/
private
boolean
isFileValid(Part file, String fileName) {
// 上传的并非文件
if
(file.getContentType() ==
null
) {
return
false
;
}
// 没有选择任何文件
else
if
(Strings.isNullOrEmpty(fileName)) {
return
false
;
}
return
true
;
}
/**
* 校验文件后缀有效
*
* @param fileName
* @return
*/
private
boolean
isImageValid(String fileName) {
for
(String suffix : imageSuffix) {
if
(fileName.endsWith(suffix)) {
return
true
;
}
}
return
false
;
}
/**
* 加速图片访问速度, 生成两级存放目录
*
* @param destFileName
* @return
*/
private
String generateTwoLevelDir(String destFileName) {
String hash = Integer.toHexString(destFileName.hashCode());
return
String.format(
"%s/%s"
, hash.charAt(
0
), hash.charAt(
1
));
}
private
String generateUUID() {
return
UUID.randomUUID().toString().replace(
"-"
,
"_"
);
}
private
String generateDestFileName(String fileName) {
String destFileName = generateUUID();
int
index = fileName.lastIndexOf(
"."
);
if
(index != -
1
) {
destFileName += fileName.substring(index);
}
return
destFileName;
}
private
String getFileName(Part part) {
String[] elements = part.getHeader(
"content-disposition"
).split(
";"
);
for
(String element : elements) {
if
(element.trim().startsWith(
"filename"
)) {
return
element.substring(element.indexOf(
"="
) +
1
).trim().replace(
"\""
,
""
);
}
}
return
null
;
}
private
void
makeDirs(String saveDir) {
File dir =
new
File(saveDir);
if
(!dir.exists()) {
dir.mkdirs();
}
}
}
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由于
getSubmittedFileName()方法需要有Tomcat 8.X以上版本的支持, 因此为了通用期间, 我们自己解析content-disposition请求头, 获取filename.
Download-下载
文件下载是向客户端响应二进制数据(而非字符),浏览器不会直接显示这些内容,而是会弹出一个下载框, 提示下载信息.
为了将资源发送给浏览器, 需要在Servlet中完成以下工作:
- 使用
Content-Type响应头来规定响应体的MIME类型, 如image/pjpeg、application/octet-stream; - 添加
Content-Disposition响应头,赋值为attachment;filename=xxx.yyy, 设置文件名; - 使用
response.getOutputStream()给浏览器发送二进制数据;
文件名中文乱码
当文件名包含中文时(attachment;filename=文件名.后缀名),在下载框中会出现乱码, 需要对文件名编码后在发送, 但不同的浏览器接收的编码方式不同:
<code> * FireFox: Base64编码 * 其他大部分Browser: URL编码 </code>
因此最好将其封装成一个通用方法:
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private
String filenameEncoding(String filename, HttpServletRequest request)
throws
IOException {
// 根据浏览器信息判断
if
(request.getHeader(
"User-Agent"
).contains(
"Firefox"
)) {
filename = String.format(
"=?utf-8?B?%s?="
, BaseEncoding.base64().encode(filename.getBytes(
"UTF-8"
)));
}
else
{
filename = URLEncoder.encode(filename,
"utf-8"
);
}
return
filename;
}
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示例-IFS下载功能
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/**
* @author jifang.
* @since 2016/5/9 17:50.
*/
@WebServlet
(name =
"ImageFileDownloadServlet"
, urlPatterns =
"/ifs_download.action"
)
public
class
ImageFileDownloadServlet
extends
HttpServlet {
@Override
protected
void
doGet(HttpServletRequest request, HttpServletResponse response)
throws
ServletException, IOException {
response.setContentType(
"application/octet-stream"
);
String fileLocation = request.getParameter(
"location"
);
String fileName = fileLocation.substring(fileLocation.lastIndexOf(
"/"
) +
1
);
response.setHeader(
"Content-Disposition"
,
"attachment;filename="
+ filenameEncoding(fileName, request));
ByteStreams.copy(
new
FileInputStream(fileLocation), response.getOutputStream());
}
@Override
protected
void
doPost(HttpServletRequest req, HttpServletResponse resp)
throws
ServletException, IOException {
doGet(req, resp);
}
}
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Async-异步处理
Servlet/Filter默认会一直占用请求处理线程, 直到它完成任务.如果任务耗时长久, 且并发用户请求量大, Servlet容器将会遇到超出线程数的风险.
Servlet 3.0 中新增了一项特性, 用来处理异步操作. 当Servlet/Filter应用程序中有一个/多个长时间运行的任务时, 你可以选择将任务分配给一个新的线程, 从而将当前请求处理线程返回到线程池中,释放线程资源,准备为下一个请求服务.
异步Servlet/Filter
- 异步支持
@WebServlet/@WebFilter注解提供了新的asyncSupport属性:
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@WebFilter
(asyncSupported =
true
)
@WebServlet
(asyncSupported =
true
)
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同样部署描述符中也添加了<async-supportted/>标签:
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<servlet>
<servlet-name>HelloServlet</servlet-name>
<servlet-
class
>com.fq.web.servlet.HelloServlet</servlet-
class
>
<async-supported>
true
</async-supported>
</servlet>
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- Servlet/Filter
支持异步处理的Servlet/Filter可以通过在ServletRequest中调用startAsync()方法来启动新线程:
| ServletRequest | 描述 |
|---|---|
AsyncContext startAsync() | Puts this request into asynchronous mode, and initializes its AsyncContext with the original (unwrapped) ServletRequest and ServletResponse objects. |
AsyncContext startAsync(ServletRequest servletRequest, ServletResponse servletResponse) | Puts this request into asynchronous mode, and initializes its AsyncContext with the given request and response objects. |
注意:
1. 只能将原始的ServletRequest/ServletResponse或其包装器(Wrapper/Decorator,详见Servlet – Listener、Filter、Decorator)传递给第二个startAsync()方法.
2. 重复调用startAsync()方法会返回相同的AsyncContext实例, 如果在不支持异步处理的Servlet/Filter中调用, 会抛出java.lang.IllegalStateException异常.
3.AsyncContext的start()方法不会造成方法阻塞.
这两个方法都返回AsyncContext实例, AsyncContext中提供了如下常用方法:
| AsyncContext | 描述 |
|---|---|
void start(Runnable run) | Causes the container to dispatch a thread, possibly from a managed thread pool, to run the specified Runnable. |
void dispatch(String path) | Dispatches the request and response objects of this AsyncContext to the given path. |
void dispatch(ServletContext context, String path) | Dispatches the request and response objects of this AsyncContext to the given path scoped to the given context. |
void addListener(AsyncListener listener) | Registers the given AsyncListener with the most recent asynchronous cycle that was started by a call to one of the ServletRequest.startAsync() methods. |
ServletRequest getRequest() | Gets the request that was used to initialize this AsyncContext by calling ServletRequest.startAsync() or ServletRequest.startAsync(ServletRequest, ServletResponse). |
ServletResponse getResponse() | Gets the response that was used to initialize this AsyncContext by calling ServletRequest.startAsync() or ServletRequest.startAsync(ServletRequest, ServletResponse). |
boolean hasOriginalRequestAndResponse() | Checks if this AsyncContext was initialized with the original or application-wrapped request and response objects. |
void setTimeout(long timeout) | Sets the timeout (in milliseconds) for this AsyncContext. |
在异步Servlet/Filter中需要完成以下工作, 才能真正达到异步的目的:
- 调用
AsyncContext的start()方法, 传递一个执行长时间任务的Runnable; - 任务完成时, 在
Runnable内调用AsyncContext的complete()方法或dispatch()方法
示例-改造文件上传
在前面的图片存储服务器中, 如果上传图片过大, 可能会耗时长久,为了提升服务器性能, 可将其改造为异步上传(其改造成本较小):
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@Override
protected
void
doPost(
final
HttpServletRequest request,
final
HttpServletResponse response)
throws
ServletException, IOException {
final
AsyncContext asyncContext = request.startAsync();
asyncContext.start(
new
Runnable() {
@Override
public
void
run() {
try
{
request.setCharacterEncoding(
"UTF-8"
);
response.setContentType(
"text/html;charset=UTF-8"
);
PrintWriter writer = response.getWriter();
Part image = request.getPart(
"image"
);
final
String fileName = getFileName(image);
if
(isFileValid(image, fileName) && isImageValid(fileName)) {
String destFileName = generateDestFileName(fileName);
String twoLevelDir = generateTwoLevelDir(destFileName);
// 保存文件
String saveDir = String.format(
"%s/%s/"
, getServletContext().getRealPath(SAVE_ROOT_DIR), twoLevelDir);
makeDirs(saveDir);
image.write(saveDir + destFileName);
// 生成外链
String ip = request.getLocalAddr();
int
port = request.getLocalPort();
String path = request.getContextPath();
String urlPrefix = String.format(
"http://%s:%s%s"
, ip, port, path);
String urlSuffix = String.format(
"%s/%s/%s"
, SAVE_ROOT_DIR, twoLevelDir, destFileName);
String url = urlPrefix + urlSuffix;
String result = String.format(
"<a href=%s>%s</a><hr/><a href=ifs_download.action?location=%s>下载</a>"
,
url,
url,
saveDir + destFileName);
writer.print(result);
}
else
{
writer.print(
"Error : Image Type Error"
);
}
asyncContext.complete();
}
catch
(ServletException | IOException e) {
LOGGER.error(
"error: "
, e);
}
}
});
}
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注意: Servlet异步支持只适用于长时间运行,且想让用户知道执行结果的任务. 如果只有长时间, 但用户不需要知道处理结果,那么只需提供一个
Runnable提交给Executor, 并立即返回即可.
AsyncListener
Servlet 3.0 还新增了一个AsyncListener接口, 以便通知用户在异步处理期间发生的事件, 该接口会在异步操作的启动/完成/失败/超时情况下调用其对应方法:
- ImageUploadListener
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/**
* @author jifang.
* @since 2016/5/10 17:33.
*/
public
class
ImageUploadListener
implements
AsyncListener {
@Override
public
void
onComplete(AsyncEvent event)
throws
IOException {
System.out.println(
"onComplete..."
);
}
@Override
public
void
onTimeout(AsyncEvent event)
throws
IOException {
System.out.println(
"onTimeout..."
);
}
@Override
public
void
onError(AsyncEvent event)
throws
IOException {
System.out.println(
"onError..."
);
}
@Override
public
void
onStartAsync(AsyncEvent event)
throws
IOException {
System.out.println(
"onStartAsync..."
);
}
}
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与其他监听器不同, 他没有@WebListener标注AsyncListener的实现, 因此必须对有兴趣收到通知的每个AsyncContext都手动注册一个AsyncListener:
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asyncContext.addListener(
new
ImageUploadListener());
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动态注册
动态注册是Servlet 3.0新特性,它不需要重新加载应用便可安装新的Web对象(
Servlet/Filter/Listener等).
API支持
为了使动态注册成为可能, ServletContext接口添加了如下方法用于 创建/添加 Web对象:
| ServletContext | 描述 |
|---|---|
| Create | |
<T extends Servlet> T createServlet(Class<T> clazz) | Instantiates the given Servlet class. |
<T extends Filter> T createFilter(Class<T> clazz) | Instantiates the given Filter class. |
<T extends EventListener> T createListener(Class<T> clazz) | Instantiates the given EventListener class. |
| Add | |
ServletRegistration.Dynamic addServlet(String servletName, Servlet servlet) | Registers the given servlet instance with this ServletContext under the given servletName. |
FilterRegistration.Dynamic addFilter(String filterName, Filter filter) | Registers the given filter instance with this ServletContext under the given filterName. |
<T extends EventListener> void addListener(T t) | Adds the given listener to this ServletContext. |
| Create & And | |
ServletRegistration.Dynamic addServlet(String servletName, Class<? extends Servlet> servletClass) | Adds the servlet with the given name and class type to this servlet context. |
ServletRegistration.Dynamic addServlet(String servletName, String className) | Adds the servlet with the given name and class name to this servlet context. |
FilterRegistration.Dynamic addFilter(String filterName, Class<? extends Filter> filterClass) | Adds the filter with the given name and class type to this servlet context. |
FilterRegistration.Dynamic addFilter(String filterName, String className) | Adds the filter with the given name and class name to this servlet context. |
void addListener(Class<? extends EventListener> listenerClass) | Adds a listener of the given class type to this ServletContext. |
void addListener(String className) | Adds the listener with the given class name to this ServletContext. |
其中addServlet()/addFilter()方法的返回值是ServletRegistration.Dynamic/FilterRegistration.Dynamic,他们都是Registration.Dynamic的子接口,用于动态配置Servlet/Filter实例.
示例-DynamicServlet
动态注册DynamicServlet, 注意: 并未使用web.xml或
@WebServlet静态注册DynamicServlet实例, 而是用DynRegListener在服务器启动时动态注册.
- DynamicServlet
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/**
* @author jifang.
* @since 2016/5/13 16:41.
*/
public
class
DynamicServlet
extends
HttpServlet {
private
String dynamicName;
@Override
protected
void
doGet(HttpServletRequest request, HttpServletResponse response)
throws
ServletException, IOException {
response.getWriter().print(
"<h1>DynamicServlet, MyDynamicName: "
+ getDynamicName() +
"</h1>"
);
}
public
String getDynamicName() {
return
dynamicName;
}
public
void
setDynamicName(String dynamicName) {
this
.dynamicName = dynamicName;
}
}
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- DynRegListener
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@WebListener
public
class
DynRegListener
implements
ServletContextListener {
@Override
public
void
contextInitialized(ServletContextEvent sce) {
ServletContext context = sce.getServletContext();
DynamicServlet servlet;
try
{
servlet = context.createServlet(DynamicServlet.
class
);
}
catch
(ServletException e) {
servlet =
null
;
}
if
(servlet !=
null
) {
servlet.setDynamicName(
"Hello fQ Servlet"
);
ServletRegistration.Dynamic dynamic = context.addServlet(
"dynamic_servlet"
, servlet);
dynamic.addMapping(
"/dynamic_servlet.do"
);
}
}
@Override
public
void
contextDestroyed(ServletContextEvent sce) {
}
}
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容器初始化
在使用类似SpringMVC这样的MVC框架时,需要首先注册DispatcherServlet到web.xml以完成URL的转发映射:
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<!-- 配置SpringMVC -->
<servlet>
<servlet-name>mvc</servlet-name>
<servlet-
class
>org.springframework.web.servlet.DispatcherServlet</servlet-
class
>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:spring/mvc-servlet.xml</param-value>
</init-param>
<load-on-startup>
1
</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>mvc</servlet-name>
<url-pattern>*.
do
</url-pattern>
</servlet-mapping>
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在Servlet 3.0中,通过Servlet容器初始化,可以自动完成Web对象的首次注册,因此可以省略这个步骤.
API支持
容器初始化的核心是javax.servlet.ServletContainerInitializer接口,他只包含一个方法:
| ServletContainerInitializer | 描述 |
|---|---|
void onStartup(Set<Class<?>> c, ServletContext ctx) | Notifies this ServletContainerInitializer of the startup of the application represented by the given ServletContext. |
在执行任何ServletContext监听器之前, 由Servlet容器自动调用onStartup()方法.
注意: 任何实现了
ServletContainerInitializer的类必须使用@HandlesTypes注解标注, 以声明该初始化程序可以处理这些类型的类.
实例-SpringMVC初始化
利用Servlet容器初始化, SpringMVC可实现容器的零配置注册.
- SpringServletContainerInitializer
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@HandlesTypes
(WebApplicationInitializer.
class
)
public
class
SpringServletContainerInitializer
implements
ServletContainerInitializer {
@Override
public
void
onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
throws
ServletException {
List<WebApplicationInitializer> initializers =
new
LinkedList<WebApplicationInitializer>();
if
(webAppInitializerClasses !=
null
) {
for
(Class<?> waiClass : webAppInitializerClasses) {
// Be defensive: Some servlet containers provide us with invalid classes,
// no matter what @HandlesTypes says...
if
(!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
WebApplicationInitializer.
class
.isAssignableFrom(waiClass)) {
try
{
initializers.add((WebApplicationInitializer) waiClass.newInstance());
}
catch
(Throwable ex) {
throw
new
ServletException(
"Failed to instantiate WebApplicationInitializer class"
, ex);
}
}
}
}
if
(initializers.isEmpty()) {
servletContext.log(
"No Spring WebApplicationInitializer types detected on classpath"
);
return
;
}
AnnotationAwareOrderComparator.sort(initializers);
servletContext.log(
"Spring WebApplicationInitializers detected on classpath: "
+ initializers);
for
(WebApplicationInitializer initializer : initializers) {
initializer.onStartup(servletContext);
}
}
}
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SpringMVC为ServletContainerInitializer提供了实现类SpringServletContainerInitializer通过查看源代码可以知道,我们只需提供WebApplicationInitializer的实现类到classpath下, 即可完成对所需Servlet/Filter/Listener的注册.
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public
interface
WebApplicationInitializer {
void
onStartup(ServletContext servletContext)
throws
ServletException;
}
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- javax.servlet.ServletContainerInitializer
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org.springframework.web.SpringServletContainerInitializer
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元数据文件<strong>javax.servlet.ServletContainerInitializer</strong>只有一行内容(即实现了<code style="font-style: inherit;">ServletContainerInitializer</code>类的全限定名),该文本文件必须放在jar包的<strong>META-INF/services</strong>目录下.
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