package com.ora.jsp.tags.generic;
import java.beans.*;
import java.io.*;
import java.lang.reflect.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
/**
* This class is a custom action for looping through the elements
* of a multi-valued bean or bean property. The bean or bean property
* must be an array, a Vector, a Dictionary or an Enumeration. The
* action body is evaluated once for each element.
*
* @author Hans Bergsten, Gefion software <hans@gefionsoftware.com>
* @version 1.0
*/
public class LoopTag extends BodyTagSupport {
// Property variables
private String name;
private String property;
private String loopId;
private String className;
// Enumeration used for iteration
private Enumeration enum;
/**
* Sets the name attribute, i.e. the name of the variable holding
* a reference to the bean with the multi-value property to loop
* through.
*
* @param name the bean variable name
*/
public void setName(String name) {
this.name = name;
}
/**
* Sets the property attribute, i.e. the name of the multi-value
* property to loop through.
*
* @param property the property name
*/
public void setProperty(String property) {
this.property = property;
}
/**
* Sets the loopId attribute, i.e. the name of the variable to
* hold the element reference in the body.
*
* @param property the property name
*/
public void setLoopId(String loopId) {
this.loopId = loopId;
}
/**
* Sets the class attribute, i.e. the name of the class for the
* multi-value property elements.
*
* @param class the element class name
*/
public void setClassName(String className) {
this.className = className;
}
/**
* Creates an Enumeration of all loop values, either using the object
* specified by the name attribute directly, or using the specified
* property. The object or the property must be one of Enumeration,
* Vector, Dictionary or Object[] (no primitive type arrays), or a
* subclass/subinterface of one of them.
*
* Makes the first element available to the body in a variable
* with the name specified by the loopId attribute.
*/
public int doStartTag() throws JspException {
Object obj = pageContext.findAttribute(name);
if (obj == null) {
throw new JspException("Variable " + name + " not found");
}
Object mvObj = obj;
try {
// Get the multi-value object using the specified property getter
// method, if any
if (property != null) {
mvObj = getProperty(obj, property);
}
enum = getEnumeration(mvObj);
}
catch (JspException e) {
throw new JspException("Error getting loop data from " + name + ": " +
e.getMessage());
}
// Set the first loop value, if any
if (enum != null && enum.hasMoreElements()) {
Object currValue = enum.nextElement();
pageContext.setAttribute(loopId, currValue);
return EVAL_BODY_TAG;
}
else {
return SKIP_BODY;
}
}
/**
* Makes the next element available to the body in a variable
* with the name specified by the loopId attribute, or returns
* SKIP_BODY if all elements have been processed.
*/
public int doAfterBody() throws JspException {
if (enum.hasMoreElements()) {
Object currValue = enum.nextElement();
pageContext.setAttribute(loopId, currValue);
return EVAL_BODY_TAG;
}
else {
return SKIP_BODY;
}
}
/**
* Writes the accumulated body contents to the JspWriter.
*/
public int doEndTag() throws JspException {
// Test if bodyContent is set, since it will be null if the
// body was never evaluated (doStartTag returned SKIP_BODY)
if (getBodyContent() != null) {
try {
getPreviousOut().print(getBodyContent().getString());
}
catch (IOException e) {}
}
return EVAL_PAGE;
}
/**
* Releases all instance variables.
*/
public void release() {
name = null;
property = null;
loopId = null;
className = null;
enum = null;
super.release();
}
/**
* Returns an Object representing an Enumeration, a Vector,
* a Dictionary or an array of objects (no primitive types),
* using the specified property getter method on the specified
* object.
*
* @param obj the Object with the multi-value property
* @param property the property name
* @return the multi-value Object
*/
private Object getProperty(Object obj, String property)
throws JspException {
Object mvObj = null;
Method method = null;
try {
BeanInfo beanInfo = Introspector.getBeanInfo(obj.getClass());
PropertyDescriptor[] pds = beanInfo.getPropertyDescriptors();
for (int i = 0; pds != null && i < pds.length; i++) {
if (pds[i].getName().equals(property)) {
method = pds[i].getReadMethod();
break;
}
}
}
catch (IntrospectionException e) {
throw new JspException("Error analyzing the bean class: " +
e.getMessage());
}
if (method == null) {
throw new JspException("Property " + property + " not found");
}
// Make sure the property is not of a primitive type
if (method.getReturnType().isPrimitive()) {
throw new JspException("Invalid property data type");
}
// Invoke the method to get the multi-value Object
Object[] args = {};
try {
mvObj = method.invoke(obj, args);
}
catch (Exception e) {
throw new JspException("Failed to get property " + property + ": " +
e.getMessage());
}
return mvObj;
}
/**
* Returns an Enumeration of the values in the specified multi-value
* object, which can be an Enumeration, Vector, Dictionary or array
* of Objects (not primitive types).
*
* @param obj the multi-value Object
* @return an Enumeration
* @exception JspException if invalid type
*/
private Enumeration getEnumeration(Object obj) throws JspException {
if (obj == null) {
return null;
}
Enumeration enum = null;
if (Enumeration.class.isAssignableFrom(obj.getClass())) {
enum = (Enumeration) obj;
}
else if (Vector.class.isAssignableFrom(obj.getClass())) {
enum = ((Vector) obj).elements();
}
else if (Dictionary.class.isAssignableFrom(obj.getClass())) {
enum = ((Dictionary) obj).elements();
}
else if (obj.getClass().isArray()) {
Object[] oa = (Object[]) obj;
Vector v = new Vector(oa.length);
for (int i = 0; i < oa.length; i++) {
v.addElement(oa[i]);
}
enum = v.elements();
}
else {
throw new JspException("Invalid data type");
}
return enum;
}
} |
