深入分析Java中webwork的文件上传机制

点击上传按钮后，webwork的程序流如下：

step 1）进入ServletDispatcher.service

public void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException {
........
request = wrapRequest(request);
.........
}

step2)进入ServletDispatcher.wrapRequest

protected HttpServletRequest wrapRequest(HttpServletRequest request)
throws IOException {
........................
if (MultiPartRequest.isMultiPart(request)) {
request = new MultiPartRequestWrapper(request, getSaveDir(), getMaxSize());
}
return request;
}

step3)进入MultiPartRequestWrapper的构造方法

public MultiPartRequestWrapper(HttpServletRequest request, String saveDir, int maxSize)
throws IOException {
.....................
//step3.1)获取webwork.preperties配置的parser
String parser = "";
parser = Configuration.getString("webwork.multipart.parser");
// If it's not set, use Pell
if (parser.equals("")) {
log.warn("Property webwork.multipart.parser not set." +
" Using com.opensymphony.webwork.dispatcher.multipart.PellMultiPartRequest");
parser = "com.opensymphony.webwork.dispatcher.multipart.PellMultiPartRequest";
}
// legacy support for old style property values
else if (parser.equals("pell")) {
parser = "com.opensymphony.webwork.dispatcher.multipart.PellMultiPartRequest";
} else if (parser.equals("cos")) {
parser = "com.opensymphony.webwork.dispatcher.multipart.CosMultiPartRequest";
} else if (parser.equals("jakarta")) {
parser = "com.opensymphony.webwork.dispatcher.multipart.JakartaMultiPartRequest";
}
//step3.2)获取后通过反射实例化parser
try {
Class baseClazz =
com.opensymphony.webwork.dispatcher.multipart.MultiPartRequest.class;
Class clazz = Class.forName(parser);
// make sure it extends MultiPartRequest
if (!baseClazz.isAssignableFrom(clazz)) {
addError("Class '" + parser + "' does not extend MultiPartRequest");
return;
}
// get the constructor
Constructor ctor = clazz.getDeclaredConstructor(new Class[]{
Class.forName("javax.servlet.http.HttpServletRequest"),
java.lang.String.class, int.class
});
// build the parameter list
Object[] parms = new Object[]{
request, saveDir, new Integer(maxSize)
};
// instantiate it
multi = (MultiPartRequest) ctor.newInstance(parms);
.................................................
}

step4 进入JakartaMultiPartRequest的构造方法（在webwork配置的parser是Jakarta所以进入了这个方法，如果你配置不同的parser回进入不同的parser

public JakartaMultiPartRequest(HttpServletRequest servletRequest, String saveDir, int maxSize)

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