抱歉这个问题的长度。我是Java的新手，我遇到了一些让我很难过的东西。我是Java的新手，我甚至不知道所有的术语，所以请耐心等待我;我有大约3年的PHP经验（主要是程序性的，不是OO），但是Java很少。我也知道使用System.out.println进行调试是错误的方法，但它可以工作，这就是我习惯的（如果你必须在这里插入关于PHP程序员的笑话）。我还在试图弄清楚如何使用NetBeans调试器。
我正在为使用Struts（1.x）的Web应用程序添加一项功能。我遇到的问题似乎是声明一个方法需要传递给它的String，但对该方法执行Reflection表示它需要String []（一个字符串数组）。我受到限制，因为我无法对应用程序进行重大的结构更改，当然我必须确保我不会破坏当前正在运行的应用程序中的任何内容，所以我正在努力使我的在那里已经存在的变化。那么，对于这个问题......
这是声明方法的地方（从这些方法中删除了很多行，只显示我希望的相关位）：
AEReportBean.java：
public class AEReportBean {
private String selectedDownloadFields = null;
public String getSelectedDownloadFields() {
return selectedDownloadFields;
}
// Note that there is no overloading of this function anywhere, this is the only declaration.
public void setSelectedDownloadFields(String selectedDownloadFields) {
this.selectedDownloadFields = selectedDownloadFields;
}
}
当用户在表单上单击“提交”时，它将由AEReportSubmitAction.java处理：
public class AEReportSubmitAction extends BaseAction {
public ActionForward doExecute(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response
) throws Exception {
// This works fine, the paramater is getting passed in the request:
System.out.println("URL parameter: " + request.getParameter("selectedDownloadFields");
AEReportBean bean = new AEReportBean(request.getLocale(), 0);
PropertyUtil.setAllFromRequest(request, bean);
// This prints "Null", meaning the setAllFromRequest line above is failing to set this property.
System.out.println("AEReportSubmitAction.java - bean.getSelectedDownloadFields() after setAllFromRequest: " + bean.getSelectedDownloadFields());
}
}
PropertyUtil.setAllFromRequest（）是魔术和真正问题发生的地方：
public class PropertyUtil {
/**
* Takes all the parameters from the request object and if there's a matching
* mutator method in the bean, sets it
*/
static public void setAllFromRequest(ServletRequest request, Object out) {
// Iterate through all the request parameter names and try to set each one.
for (Enumeration parameterNames = request.getParameterNames(); parameterNames.hasMoreElements();) {
String name = (String) parameterNames.nextElement();
try {
PropertyUtil.setSimpleProperty(out, name, request.getParameter(name));
}
catch (Exception e) {
log.info("Exception while setting properties from the Request. parameterName=" + name, e);
}
}
}
/**
* Sets the property from an object using the object's mutator method.
* Assumes naming conventions for accessor methods
* @param bean the object to get the property from
* @param property the name of the property to obtain
* @param newProperty the object to set
*/
// NOTE: This just seems to be a wrapper for the method below it...
static public void setSimpleProperty(Object bean, String property, Object newProperty) throws Exception {
PropertyUtil.setSimpleProperty(bean, property, newProperty, null);
}
/**
* Sets the property from an object using the object's mutator method.
* Assumes naming conventions for accessor methods
* @param bean the object to get the property from
* @param property the name of the property to obtain
* @param newProperty the object to set
*/
static public void setSimpleProperty(Object bean, String property, Object newProperty, Class type) throws Exception {
// Capitalize the first letter in the property and append "set" to the front
String methodName = "set" + property.substring(0, 1).toUpperCase() + property.substring(1);
Method method;
Class[] parameters;
// If the Type was passed in when this method was called, simply add it to the Class array.
if (type != null) {
parameters = new Class[]{type};
}
// If the Type was not specified, determine the Type's class by calling getClass() on it; that class will be used below to call the appropriate setter method.
else {
parameters = new Class[]{newProperty.getClass()};
}
// Here's the reflection problem...
// Iterate through all the methods in the bean. If the method is named "setSelectedDownloadFields", print out some info about it.
for (Method m : bean.getClass().getMethods()) {
if (m.getName().equals("setSelectedDownloadFields")) {
// newProperty is the incoming data that ultimately comes from the HTML form field.
System.out.println("newProperty.getClass(): " + newProperty.getClass()); // Prints "class java.lang.String"
// Added for Cameron Skinner in comments.
System.out.println("m.toGenericString: " + m.toGenericString()); // Prints "public void com.[company deleted].bean.AEReportBean.setSelectedDownloadFields(java.lang.String[])"
System.out.println("m.getName(): " + m.getName()); // Prints "setSelectedDownloadFields"
System.out.println("parameters:");
for (Class c : m.getParameterTypes()) {
System.out.println("--c.getCanonicalName(): " + c.getCanonicalName()); // Prints "java.lang.String[]"
System.out.println("--c.getName(): " + c.getName()); // Prints "[Ljava.lang.String;"
}
}
}
// And here's where it fails...
try {
System.out.println("bean.getClass(): " + bean.getClass()); // Prints "class com.[company deleted].bean.AEReportBean"
System.out.println("methodName: " + methodName); // Prints "setSelectedDownloadFields"
System.out.println("for (Class p : parameters):");
for (Class p : parameters) {
System.out.println("--p.getCanonicalName(): " + p.getCanonicalName()); // Prints "java.lang.String"
}
// Here it looks for a method called, effectively, AEReportBean.setSelectedDownloadFields(String s), but above we see that reflection is showing it as AEReportBean.setSelectedDownloadFields(String[] s), so the try block fails.
method = bean.getClass().getMethod(methodName, parameters);
}
catch (NoSuchMethodException e) {
// All lines below here also fail until it bombs out with the exception at the bottom...
// If no method can be found, then see if it's a primitive type that
// has been wrapped
Class valueClass = newProperty.getClass();
//System.out.println("valueClass.toString() = " + valueClass.toString());
try {
if (valueClass.equals(Integer.class)) {
method = bean.getClass().getMethod(methodName, new Class[]{int.class});
}
else if (valueClass.equals(Double.class)) {
method = bean.getClass().getMethod(methodName, new Class[]{double.class});
}
else if (valueClass.equals(Long.class)) {
method = bean.getClass().getMethod(methodName, new Class[]{long.class});
}
else if (valueClass.equals(Float.class)) {
method = bean.getClass().getMethod(methodName, new Class[]{float.class});
}
else {
throw new Exception(e.getMessage());
}
}
catch (NoSuchMethodException ex) {
throw new Exception(ex.getMessage());
}
}
// If it had gotten to this point, it would call the method with the appropriate parameters, and the property would be set.
try {
// Now execute the method
method.invoke(bean, new Object[]{newProperty});
}
catch (Exception ex) {
throw new Exception(ex.getMessage());
}
}
}
我真的不知道我在这里缺少什么，但必须有一些东西。同一页面上的其他HTML表单元素完美运行。如果需要更多信息，请告诉我。谢谢！
答案 0 :(得分：4)
代码结果不是谎言。它基本上告诉我们这个课程不是你所期望的。您在项目的类路径中有多个AEReportBean个不同版本的类，可能在不同的包中，并且在类加载中导入了错误的类或优先级。在Netbeans中进行类型/类搜索，以在类路径中按给定名称查找所有类（我不做Netbeans，但在Eclispe中它是Ctrl + Shift + T，Netbeans等效可能是Alt + Shift + O ）
更新：另一个可能的原因是Netbeans在保存源文件时没有自动构建项目（IDE应该在构建期间创建/刷新.class文件）。看看设置中的某个地方。