很抱歉这个问题太长了。 我是 Java 新手，我遇到了一些真正难倒我的事情。 我对 Java 还很陌生，我什至还不知道所有术语，所以请耐心等待；我有大约 3 年的 PHP 经验（主要是过程性的，而不是 OO），但很少有 Java 经验。 我也知道使用 System.out.println 进行调试是错误的方法，但它有效，而且是我所习惯的（如果必须的话，请在此处插入有关 PHP 程序员的笑话）。 我仍在尝试弄清楚如何使用 NetBeans 调试器。
我正在努力向使用 Struts (1.x) 的 Web 应用程序添加一项功能。 我遇到的问题似乎是一个方法被声明为想要将 String 传递给它，但是对该方法进行反射表明它需要 String[] （字符串数组）。 我受到限制，因为我无法真正对应用程序进行重大结构更改，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，所以我试图使我的已经存在的环境中的变化。 那么，对于这个问题...
这里是声明该方法的位置（从这些内容中删除了许多行以仅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;
}
}
当用户单击表单上的“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() 是神奇的地方，也是真正的问题发生的地方：
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错过了什么，但一定有什么。 同一页面上的其他 HTML 表单元素可以完美运行。 如果需要更多信息，请告诉我。 谢谢！
代码结果不会说谎。这基本上表明该类不是您所期望的那样。您的项目的类路径中有多个不同版本的
AEReportBean更新：另一个可能的原因是 Netbeans 没有在保存源文件时自动构建项目（IDE 应在构建期间创建/刷新
.class