struts源码之八
创建完成ActionContext后，strtus2将当Dispatcher分配到当前线程。
prepare.assignDispatcherToThread();
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public void assignDispatcherToThread() { Dispatcher.setInstance(dispatcher); }?
到底是怎么初始化分配的，其实也是放入ThreadLocal中，仔细看
/** * Store the dispatcher instance for this thread. * * @param instance The instance */ public static void setInstance(Dispatcher instance) { Dispatcher.instance.set(instance); }?
/** * Provide a thread local instance. */ private static ThreadLocal<Dispatcher> instance = new ThreadLocal<Dispatcher>();
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预处理完成后就判断是否有不需要处理的请求，如果有则 struts不处理，继续执行, 否则struts2过滤过来进行处理
if ( excludedPatterns != null && prepare.isUrlExcluded(request, excludedPatterns)) {chain.doFilter(request, response);}
?然后就开始处理了，首先是包装requst
request = prepare.wrapRequest(request);
为什么要包装requst呢？因为是为了处理文件上传 multipart/form-data
public HttpServletRequest wrapRequest(HttpServletRequest oldRequest) throws ServletException { HttpServletRequest request = oldRequest; try { // Wrap request first, just in case it is multipart/form-data // parameters might not be accessible through before encoding (ww-1278) request = dispatcher.wrapRequest(request, servletContext); } catch (IOException e) { String message = "Could not wrap servlet request with MultipartRequestWrapper!"; throw new ServletException(message, e); } return request; }?
核心的处理是dispatcher.wrapRequst
public HttpServletRequest wrapRequest(HttpServletRequest request, ServletContext servletContext) throws IOException { // don't wrap more than once if (request instanceof StrutsRequestWrapper) { return request; } String content_type = request.getContentType(); if (content_type != null && content_type.contains("multipart/form-data")) { MultiPartRequest mpr = null; //check for alternate implementations of MultiPartRequest Set<String> multiNames = getContainer().getInstanceNames(MultiPartRequest.class); if (multiNames != null) { for (String multiName : multiNames) { if (multiName.equals(multipartHandlerName)) { mpr = getContainer().getInstance(MultiPartRequest.class, multiName); } } } if (mpr == null ) { mpr = getContainer().getInstance(MultiPartRequest.class); } request = new MultiPartRequestWrapper(mpr, request, getSaveDir(servletContext)); } else { request = new StrutsRequestWrapper(request); } return request; }?
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首先是通过request获取getContentType
?String content_type = request.getContentType();
然后判断，如果请求中包含multipart/form-data
则创建一个MultiPartRequestWrapper，然后返回，否则创建一个通用的StrutsRequestWrapper
MultiPartRequestWrapper和StrutsRequestWrapper到底是什么关系？
通过源码可以看到，其实
MultiPartRequestWrapper本身继承自StrutsRequestWrapper,
它比StrutsRequestWrapper做了更多的事，就是文件上传的处理
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public class MultiPartRequestWrapper extends StrutsRequestWrapper { protected static final Logger LOG = LoggerFactory.getLogger(MultiPartRequestWrapper.class); Collection<String> errors; MultiPartRequest multi; /** * Process file downloads and log any errors. * * @param request Our HttpServletRequest object * @param saveDir Target directory for any files that we save * @param multiPartRequest Our MultiPartRequest object */ public MultiPartRequestWrapper(MultiPartRequest multiPartRequest, HttpServletRequest request, String saveDir) { super(request); multi = multiPartRequest; try { multi.parse(request, saveDir); for (Object o : multi.getErrors()) { String error = (String) o; addError(error); } } catch (IOException e) { addError("Cannot parse request: "+e.toString()); } } /** * Get an enumeration of the parameter names for uploaded files * * @return enumeration of parameter names for uploaded files */ public Enumeration<String> getFileParameterNames() { if (multi == null) { return null; } return multi.getFileParameterNames(); } /** * Get an array of content encoding for the specified input field name or <tt>null</tt> if * no content type was specified. * * @param name input field name * @return an array of content encoding for the specified input field name */ public String[] getContentTypes(String name) { if (multi == null) { return null; } return multi.getContentType(name); } /** * Get a {@link java.io.File[]} for the given input field name. * * @param fieldName input field name * @return a File[] object for files associated with the specified input field name */ public File[] getFiles(String fieldName) { if (multi == null) { return null; } return multi.getFile(fieldName); } /** * Get a String array of the file names for uploaded files * * @param fieldName Field to check for file names. * @return a String[] of file names for uploaded files */ public String[] getFileNames(String fieldName) { if (multi == null) { return null; } return multi.getFileNames(fieldName); } /** * Get the filename(s) of the file(s) uploaded for the given input field name. * Returns <tt>null</tt> if the file is not found. * * @param fieldName input field name * @return the filename(s) of the file(s) uploaded for the given input field name or * <tt>null</tt> if name not found. */ public String[] getFileSystemNames(String fieldName) { if (multi == null) { return null; } return multi.getFilesystemName(fieldName); } /** * @see javax.servlet.http.HttpServletRequest#getParameter(String) */ public String getParameter(String name) { return ((multi == null) || (multi.getParameter(name) == null)) ? super.getParameter(name) : multi.getParameter(name); } /** * @see javax.servlet.http.HttpServletRequest#getParameterMap() */ public Map getParameterMap() { Map<String, String[]> map = new HashMap<String, String[]>(); Enumeration enumeration = getParameterNames(); while (enumeration.hasMoreElements()) { String name = (String) enumeration.nextElement(); map.put(name, this.getParameterValues(name)); } return map; } /** * @see javax.servlet.http.HttpServletRequest#getParameterNames() */ public Enumeration getParameterNames() { if (multi == null) { return super.getParameterNames(); } else { return mergeParams(multi.getParameterNames(), super.getParameterNames()); } } /** * @see javax.servlet.http.HttpServletRequest#getParameterValues(String) */ public String[] getParameterValues(String name) { return ((multi == null) || (multi.getParameterValues(name) == null)) ? super.getParameterValues(name) : multi.getParameterValues(name); } /** * Returns <tt>true</tt> if any errors occured when parsing the HTTP multipart request, <tt>false</tt> otherwise. * * @return <tt>true</tt> if any errors occured when parsing the HTTP multipart request, <tt>false</tt> otherwise. */ public boolean hasErrors() { return !((errors == null) || errors.isEmpty()); } /** * Returns a collection of any errors generated when parsing the multipart request. * * @return the error Collection. */ public Collection<String> getErrors() { return errors; } /** * Adds an error message. * * @param anErrorMessage the error message to report. */ protected void addError(String anErrorMessage) { if (errors == null) { errors = new ArrayList<String>(); } errors.add(anErrorMessage); } /** * Merges 2 enumeration of parameters as one. * * @param params1 the first enumeration. * @param params2 the second enumeration. * @return a single Enumeration of all elements from both Enumerations. */ protected Enumeration mergeParams(Enumeration params1, Enumeration params2) { Vector temp = new Vector(); while (params1.hasMoreElements()) { temp.add(params1.nextElement()); } while (params2.hasMoreElements()) { temp.add(params2.nextElement()); } return temp.elements(); }}?
而StrutsRequestWrapper只有一个核心的方法就是getAttribute，
getAttribute的到底到哪里去取得值呢？
其实是到ValueStack中取值，我们所有的请求都被struts2添加到ValueStack中了。
ValueStack stack = ctx.getValueStack(); if (stack != null) { attribute = stack.findValue(s); }?
回到MultiPartRequestWrapper中，
我们知道，当struts2处理文件上传时，支持多文件上传，而且只要在我们的 action中声明
File[] file，
String[] fileName即可，
原因是MultiPartRequest
是这个接口在搞鬼
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public interface MultiPartRequest { public void parse(HttpServletRequest request, String saveDir) throws IOException; /** * Returns an enumeration of the parameter names for uploaded files * * @return an enumeration of the parameter names for uploaded files */ public Enumeration<String> getFileParameterNames(); /** * Returns the content type(s) of the file(s) associated with the specified field name * (as supplied by the client browser), or <tt>null</tt> if no files are associated with the * given field name. * * @param fieldName input field name * @return an array of content encoding for the specified input field name or <tt>null</tt> if * no content type was specified. */ public String[] getContentType(String fieldName); /** * Returns a {@link java.io.File} object for the filename specified or <tt>null</tt> if no files * are associated with the given field name. * * @param fieldName input field name * @return a File[] object for files associated with the specified input field name */ public File[] getFile(String fieldName); /** * Returns a String[] of file names for files associated with the specified input field name * * @param fieldName input field name * @return a String[] of file names for files associated with the specified input field name */ public String[] getFileNames(String fieldName); /** * Returns the file system name(s) of files associated with the given field name or * <tt>null</tt> if no files are associated with the given field name. * * @param fieldName input field name * @return the file system name(s) of files associated with the given field name */ public String[] getFilesystemName(String fieldName); /** * Returns the specified request parameter. * * @param name the name of the parameter to get * @return the parameter or <tt>null</tt> if it was not found. */ public String getParameter(String name); /** * Returns an enumeration of String parameter names. * * @return an enumeration of String parameter names. */ public Enumeration<String> getParameterNames(); /** * Returns a list of all parameter values associated with a parameter name. If there is only * one parameter value per name the resulting array will be of length 1. * * @param name the name of the parameter. * @return an array of all values associated with the parameter name. */ public String[] getParameterValues(String name); /** * Returns a list of error messages that may have occurred while processing the request. * If there are no errors, an empty list is returned. If the underlying implementation * (ie: pell, cos, jakarta, etc) cannot support providing these errors, an empty list is * also returned. This list of errors is repoted back to the * {@link MultiPartRequestWrapper}'s errors field. * * @return a list of Strings that represent various errors during parsing */ public List getErrors();}?
看了源码详细不用仔细说什么也能明白
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这个类的实现类只有一个，那就是JakartaMultiPartRequest专门用来处理文件上传
我们看到它默认的属性
protected Map<String,List<FileItem>> files = new HashMap<String,List<FileItem>>(); // maps parameter name -> List of param values protected Map<String,List<String>> params = new HashMap<String,List<String>>(); // any errors while processing this request protected List<String> errors = new ArrayList<String>(); protected long maxSize;
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这就是我们的action中为什么实现文件上传是如此的容易，而且支持多文件上传。
当我们调用getFiles的时候，其实是调用JakartaMultiPartRequest中的getFile
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public File[] getFile(String fieldName) { List<FileItem> items = files.get(fieldName); if (items == null) { return null; } List<File> fileList = new ArrayList<File>(items.size()); for (FileItem fileItem : items) { File storeLocation = ((DiskFileItem) fileItem).getStoreLocation(); if(fileItem.isInMemory() && storeLocation!=null && !storeLocation.exists()) { try { storeLocation.createNewFile(); } catch (IOException e) { if(LOG.isErrorEnabled()){ LOG.error("Cannot write uploaded empty file to disk: " + storeLocation.getAbsolutePath(),e); } } } fileList.add(storeLocation); } return fileList.toArray(new File[fileList.size()]); }?
这样把request就包装成strtus2的request了。可以处理普通请求和文件上传请求。
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