Struts2 HttpServletRequest获取请求参数的过程

1. 编写一个简单的Action

public class UserAction {
    private String name;
    public String execute(){
        System.out.println("执行execute方法...");//加断点
        System.out.println("name========"+name);
        return "success";
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

2. 启动Tomcat服务器调试运行

3. 查看代码执行顺序

4. 打开Dispather的serviceAction方法

  public void serviceAction(HttpServletRequest request, HttpServletResponse response, ActionMapping mapping)
            throws ServletException {
        //在下面一行代码加断点再次调试运行
        Map<String, Object> extraContext = createContextMap(request, response, mapping);
        .....
   在该行按F5键进入如下代码
       public Map<String,Object> createContextMap(request, response,mapping) {
        Map requestMap = new RequestMap(request);
        从以下注释可以看出参数request获取参数的方式，存在Map中
        // parameters map wrapping the http parameters.  ActionMapping parameters are now handled and applied separately
        HttpParameters params = HttpParameters.create(request.getParameterMap()).build();
在build方法按F3可以看到如下代码
public HttpParameters build() {
...
   for (Map.Entry<String, Object> entry : requestParameterMap.entrySet()) {
     String name = entry.getKey();
     Object value = entry.getValue();
     parameters.put(name, new Parameter.Request(name, value));
    }
    return new HttpParameters(parameters);
}
可以看出把请求参数的Map包装成HttpParameters
最后创建一个map
Map<String,Object> extraContext = createContextMap(requestMap, params, session, application, request, response);
....
return extraContext;

5. 查看具体参数位置

public void serviceAction(request, response, mapping)
            throws ServletException {
//加断点调试
        Map<String, Object> extraContext = createContextMap(request, response, mapping);
 // If there was a previous value stack, ....
ValueStack stack = .....;   
查看extraContext 变量中的数据如下图所示，可以看到调用Action时传入的参数:http://localhost:8080/strutsdemo/userAction?name=admin      

这就是Struts2获取请求参数的过程。