JSP自定义标签

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实际使用：

<td style="text-align: center;">
  	<b:Call type="com.techson.util.DateUtil" method="dateToStr"  var="checkin">
		<b:Param paramclass="java.util.Date"  value="${vo.checkin}" />
		<b:Param paramclass="java.lang.String" value="@dd@-@MMM@-@yy@" />
	</b:Call>
  	${checkin}
</td>

输出的日期是Date类型，在dateToStr方法中将其格式化并转化为String类型显示，如

标签引入：

<%@ taglib uri="/WEB-INF/utils.tld" prefix="b"%>

utils.tld:

<?xml version="1.0" encoding="UTF-8"?>
<taglib version="2.0" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee web-jsptaglibrary_2_0.xsd">
  <tlib-version>1.0</tlib-version>
  <short-name>utils</short-name>
  <uri>/WEB-INF/utils</uri>
  <tag>
    <name>Call</name>
    <tag-class>tags.Call</tag-class>
    <body-content>scriptless</body-content>
    <attribute>
      <name>bean</name>
      <required>false</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.Object</type>
    </attribute>
    <attribute>
      <name>type</name>
      <required>false</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.String</type>
    </attribute>
    <attribute>
      <name>method</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.String</type>
    </attribute>
    <attribute>
      <name>var</name>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.String</type>
    </attribute>
    <attribute>
      <name>scope</name>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.String</type>
    </attribute>
    <dynamic-attributes>true</dynamic-attributes>
  </tag>

  <tag>
    <name>Param</name>
    <tag-class>tags.ParamTag</tag-class>
    <body-content>empty</body-content>
    <attribute>
      <name>paramclass</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.String</type>
    </attribute>
    <attribute>
      <name>value</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.Object</type>
    </attribute>
  </tag>
</taglib>

tags.ParamTag.java类：

package tags;
import javax.servlet.jsp.JspException;

public class ParamTag extends SimpleTagSupport {

    private java.lang.String _class;
    private java.lang.Object value;
    
    public void doTag() throws JspException {
        StrictTypeParams parent = (StrictTypeParams)findAncestorWithClass(this, StrictTypeParams.class);
		//调用父标签,即b:call
        if (parent == null) {
            throw new JspException("The Param tag is not enclosed by a supported tag type");
        }
        parent.addStrictTypeParameter(this._class, this.value);  
		//addStr..是父标签中方法
        
    }    

    /**
     * Setter for the class attribute.
     */
    public void setParamclass(java.lang.String value) {
        this._class = value;
    }   
    public void setValue(java.lang.Object value) {
        this.value = value;
    }
}

StrictTypeParams：一个引用父标签的接口

package tags;  
 
	public interface StrictTypeParams {  
		void addStrictTypeParameter(String type, Object value);  
	}

tags.Call.java类：

 * Call.java

package tags;

import java.lang.reflect.Method;

public class Call extends SimpleTagSupport implements DynamicAttributes, StrictTypeParams  {
    
    /**
     * Initialization of bean property.
     */
    private java.lang.Object bean;
    
    private java.lang.String type;
    
    private java.lang.String method;    
   
    private java.lang.String var = null;
   
    private int scope = PageContext.PAGE_SCOPE;
    private List dynamicAttrValues = new ArrayList();
    private List typeList = null;
    
	//doTag()为标签默认执行方法
    public void doTag() throws JspException {
    	
        JspWriter out=getJspContext().getOut();
        try {
            JspFragment f=getJspBody();
            if (f != null) f.invoke(out);
        } catch (java.io.IOException ex) {
            throw new JspException(ex.getMessage());
        }
        boolean isStaticMethod = this.type!=null?true:false;
        Class cls = null;
    	if(isStaticMethod){
    		try {
    			cls = Class.forName(this.type);
    		} catch (ClassNotFoundException e1) {
    			throw new JspException("Class not be found for your type!");
    		}
    	}else{
    		cls = bean.getClass();
    	}
        Method[] methods = cls.getMethods();
        Method m = null;
        Class[] paramTypes = null;
        
        Method : for (int i = 0; i < methods.length; i++ ) {
            Method t = methods[i];
            paramTypes = t.getParameterTypes();  //这个方法的参数类型的集合
            if (t.getName().equals(method) && paramTypes.length == dynamicAttrValues.size()) {
                if (typeList != null){
                    for (int j = 0; j < paramTypes.length; j++){
                        if (!paramTypes[j].getName().equals(typeList.get(j))){
                        	continue Method;
                        }
                    }
                }
                m = t;
                break;
            }
        }
        
        if (m == null)
            throw new JspException("JavaBean Object hasn't no method named '" + method + "'");
        
        try {
            Object coercedValues[] = new Object[paramTypes.length];
            Iterator paramIterator = dynamicAttrValues.iterator();
            for (int i = 0; i < paramTypes.length; i++) {
                Object paramValue = paramIterator.next();
                Class paramClass = paramTypes[i];
                if (paramValue == null || paramValue.getClass() != paramClass)
                    try {
                        paramValue = Coercions.coerce(paramValue, paramClass, null);
                    } catch (ELException e) {
                        throw new JspException(e.getMessage(), e.getRootCause());
                    }
                coercedValues[i] = paramValue;
            }
            Object returnVal = null;
            if(isStaticMethod){
            	returnVal = m.invoke(null, coercedValues);
            }else{
            	returnVal = m.invoke(bean, coercedValues);
            }
            if (var != null)
                if (returnVal != null)
                    getJspContext().setAttribute(var, returnVal, scope);
                else
                    getJspContext().removeAttribute(var, scope);
            
        } catch (Exception ex) {
            ex.printStackTrace();
            throw new JspException("Call method is Error!");
        }
        
    }
    
    /**
     * Setter for the bean attribute.
     */
    public void setBean(java.lang.Object value) throws JspException {
        if (value == null)
            throw new JspException("Null 'bean' attribute in 'Call' tag");
        this.bean = value;
    }
    
    /**
     * Setter for the method attribute.
     */
    public void setMethod(java.lang.String value) throws JspException {
        if (value == null)
            throw new JspException("Null 'method' attribute in 'Call' tag");
        this.method = value;
    }
    
    /**
     * Setter for the var attribute.
     */
    public void setVar(java.lang.String value) throws JspException {
        if (value == null)
            throw new JspException("Null 'var' attribute in 'Call' tag");
        this.var = value;
    }
    
    /**
     * Setter for the scope attribute.
     */
    public void setScope(java.lang.String value) {
        if (value.equalsIgnoreCase("page"))
            scope = PageContext.PAGE_SCOPE;
        else if (value.equalsIgnoreCase("request"))
            scope = PageContext.REQUEST_SCOPE;
        else if (value.equalsIgnoreCase("session"))
            scope = PageContext.SESSION_SCOPE;
        else if (value.equalsIgnoreCase("application"))
            scope = PageContext.APPLICATION_SCOPE;
    }
    
    public void setDynamicAttribute(String uri, String localName, Object value) throws JspException {
        dynamicAttrValues.add(value);
    }

    public void addStrictTypeParameter(String type, Object value) {
        if (typeList == null)
            typeList = new ArrayList();
        typeList.add(type);
        dynamicAttrValues.add(value);
    }

	public void setType(java.lang.String type) {
		this.type = type;
	}
	
	public static void main(String[] agrs) throws ClassNotFoundException, JspException{
	    String type = "com.techson.util.DateUtil";
	    String method="dateDiff";
	    
	   List dynamicAttrValues = new ArrayList();
	   List typeList = new ArrayList();
	   
	   typeList.add("java.lang.Boolean");
       dynamicAttrValues.add(true);
       
       Class cls = Class.forName(type);
       Method[] methods = cls.getMethods();
       Method m = null;
       
       Class[] paramTypes = null;
       Method : for (int i = 0; i < methods.length; i++ ) {
           Method t = methods[i];
           paramTypes = t.getParameterTypes();
           if (t.getName().equals(method) && paramTypes.length == dynamicAttrValues.size()) {
               if (typeList != null){
                   for (int j = 0; j < paramTypes.length; j++){
                       if (!paramTypes[j].getName().equals(typeList.get(j))){
                    	   continue Method;
                       }
                   }
               }
               m = t;
               break;
           }
       }
       if (m == null)
           throw new JspException("JavaBean Object hasn't no method named '" + method + "'");
       
       try {
           Object coercedValues[] = new Object[paramTypes.length];
           Iterator paramIterator = dynamicAttrValues.iterator();
           for (int i = 0; i < paramTypes.length; i++) {
               Object paramValue = paramIterator.next();
               Class paramClass = paramTypes[i];
               System.out.println(paramClass);
               if (paramValue == null || paramValue.getClass() != paramClass)
                   try {
                	   System.out.println(paramValue.getClass() + "/ "+ paramClass);
                       paramValue = Coercions.coerce(paramValue, paramClass, null);
                   } catch (ELException e) {
                       throw new JspException(e.getMessage(), e.getRootCause());
                   }
               coercedValues[i] = paramValue;
           }
           Object returnVal = null;
           	returnVal = m.invoke(null, coercedValues);
           	System.out.print(returnVal);
       } catch (Exception ex) {
           ex.printStackTrace();
           throw new JspException("Call method is Error!");
       }
	}
}

处理方法DateUtils.java中方法dateToStr：

public static String dateToStr(Calendar cal , String format) {
		if(format.contains("@y")){
			int _y = cal.get(Calendar.YEAR);
			String _yyyy = new DecimalFormat("0000").format(_y);
			String _yy = _yyyy.substring(2);
			format = format.replaceAll("@[y]{4}@",_yyyy)
			.replaceAll("@[y]{2}@",_yy)
			.replaceAll("@[y]{1}@","" + _y);
		}
		
		if(format.contains("@M")){
			int _M= cal.get(Calendar.MONTH) + 1;
			String _MM = (_M<10)?"0"+_M:"" + _M;
			String _MMM = Constants.MTH[_M - 1];
			format=format.replaceAll("@MMM@",_MMM);
			format=format.replaceAll("@MM@",_MM);
			format=format.replaceAll("@M@","" + _M);
		}
		
		if(format.contains("@d")){
			int _D= cal.get(Calendar.DATE);
			String _DD=(_D<10)?"0"+_D:""+_D;
			format=format.replaceAll("@dd@",_DD);
			format=format.replaceAll("@d@","" +_D);
		}
		
		if(format.contains("@h")){
			int _h=cal.get(Calendar.HOUR_OF_DAY);
			String _hh=(_h<10)?"0"+_h:"" +_h;
			format=format.replaceAll("@hh@",_hh);
			format=format.replaceAll("@h@","" + _h);
		}
		
		if(format.contains("@m")){
			int _m=cal.get(Calendar.MINUTE);
			String _mm=(_m<10)?"0"+_m:""+_m;
			format=format.replaceAll("@mm@",_mm);
			format=format.replaceAll("@m@","" + _m);
		}
		
		if(format.contains("@s")){
			int _s=cal.get(Calendar.SECOND);
			String _ss=(_s<10)?"0"+_s:"" + _s;
			format=format.replaceAll("@ss@",_ss);
			format=format.replaceAll("@s@","" + _s);
		}
		
		if(format.contains("@W")){
			int _W=cal.get(Calendar.DAY_OF_WEEK);
			format=format.replaceAll("@WWW@",Constants.WEEK[_W-1]);
			format=format.replaceAll("@WW@",Constants.WEK[_W-1]);
			format=format.replaceAll("@W@","" + (_W-1));
		}
		return format;
	}
	
	public static String dateToStr(Date d , String format) {
		Calendar cal = Calendar.getInstance();
		cal.setTime(d);
		return dateToStr(cal,format);
	}

参考：http://zengsun.iteye.com/category/25493?show_full=true

http://www.ibm.com/developerworks/cn/java/j-lo-jsp2tag/index.html?ca=drs-

http://blog.csdn.net/zavens/article/details/1685615

findAncestorWithClass：

http://www.ibm.com/developerworks/cn/java/j-taglib/

getParameterTypes：

http://download.oracle.com/javase/1.4.2/docs/api/java/lang/reflect/Method.html#getParameterTypes%28%29