自定义标签（下）

一时失言乱红尘 2024-03-16 23:38 92阅读 0赞

## 一.for标签 ##

### 1.定义： ###

> JSP中的for标签是JSTL中的**核心标签库之一**，用于迭代一个集合（比如数组、列表等）并在循环体中进行一些操作。`<c:forEach>` 标签非常类似**于Java中的for循环**，它支持多种循环控制语句，如break、continue、varStatus 等。

### 2.语法： ###

<c:forEach var="item" items="${collection}">
       
    </c:forEach>

> 其中，`var` 参数指定了一个**在每次循环中声明的局部变量名，并且该变量的值会设置为当前迭代中的集合元素。**而`items`参数**指定了要循环的集合。**
> 
> 在循环体中，可以使用 `${item}` 表达式引用变量或者在表达式中使用 `varStatus` 变量访问迭代的状态信息。

### 3.自定义for标签 ###

#### 1.建立实现类 ####

![adf47334237a4706a5d5eabc472527b4.png][]

![2609efe6f5224b6fbc826f616ca2c935.png][]

package com.lz.text;
    
    import java.util.ArrayList;
    import java.util.Iterator;
    import java.util.List;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.tagext.BodyTagSupport;
    
    public class Text1 extends BodyTagSupport {
    
    	/***
    	 * fore标签
    	 * 
    	 * <c:forEach items="${}" var="c"
    	 * 
    	 * items 类型:list  
    	 *  var 类型:string 线路：
    	 *   第二条： eval_boby_include 
    	 *   第三条： eval_boby_again
    	 * 
    	 */
    	//数据源遍历
    	private List<Object> items =new ArrayList<Object>();
    	//对象指针 
    	private String var;
    
    	/**
    	 * @return the items
    	 */
    	public List<Object> getItems() {
    		return items;
    	}
    
    	/**
    	 * @param items
    	 *            the items to set
    	 */
    	public void setItems(List<Object> items) {
    		this.items = items;
    	}
    
    	/**
    	 * @return the var
    	 */
    	public String getVar() {
    		return var;
    	} 
    
    	public Text1() {
    		super();
    	}
    
    	/**
    	 * @param var
    	 *            the var to set
    	 */
    	public void setVar(String var) {
    		this.var = var;
    	}
    
    	@Override
    	public int doStartTag() throws JspException {
    		//第一条线路
    		if (items==null||items.size()==0) {
    			return    SKIP_BODY;
    		}
    		// 定义迭代器
    		Iterator<Object> it = items.iterator();
    		//获取数据源2，3数据
    		pageContext.setAttribute(var, it.next());
    		// 为了保留迭代器指针现有的位置
    		pageContext.setAttribute("it", it);
    		return EVAL_BODY_INCLUDE;
    	}
    
    	@Override
    	public int doAfterBody() throws JspException {
    		Iterator<Object> it = (Iterator<Object>) pageContext.getAttribute("it");
    		if (it.hasNext()) {
    			//获取第一数据
    			pageContext.setAttribute(var, it.next());
    			// 为了保留迭代器指针现有的位置
    			pageContext.setAttribute("it", it);
    			return EVAL_BODY_AGAIN;
    		}else {
    			return  EVAL_PAGE;
    		}
    		
    	}
    
    }

#### 2.建立tid类 ####

![fb98c732ebdd49c6b33aea4bafb3f050.png][]

<tag>
    		<name>for</name>
    		<tag-class>com.lz.text.Text1</tag-class>
    		
    		<body-content>jsp</body-content>
    		<attribute>
    			<name>items</name>
    			<required>true</required>
    			<rtexprvalue>true</rtexprvalue>
    		</attribute>
    		
    		<attribute>
    			<name>var</name>
    			<required>true</required>
    			<rtexprvalue>false</rtexprvalue>
    		</attribute>
    	</tag>

#### 3.实现功能 ####

![b918be796e5c4b728481186988dbbf65.png][]

## 二.数字标签 ##

### 1.作用 ###

> **当某些数据作用于多个页面时，或者频繁使用，就可以做成数据标签，减少代码**

### 2.自定义数字标签 ###

#### 1.建立实现类 ####

![5abdeb961301400dabe2923741b43fe2.png][]

package com.lz.text;
    
    import java.util.ArrayList;
    import java.util.Iterator;
    import java.util.List;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.JspWriter;
    import javax.servlet.jsp.tagext.BodyTagSupport;
    
    public class Text2 extends BodyTagSupport {
    /**
     * 数据标签 
     */
    	//存储数据名称
    	private    String  var;
    /**
     * @return the var
     */
    public String getVar() {
    	return var;
    }
    /**
     * @param var the var to set
     */
    public void setVar(String var) {
    	this.var = var;
    }
    public Text2(String var) {
    	super();
    	this.var = var;
    }
    public Text2() {
    	super();
    }
    	@Override
    		public int doStartTag() throws JspException {
    			JspWriter out = pageContext.getOut();
    			//模拟数据
    			List<Stu> list = new ArrayList<Stu>();
    			   list.add(new  Stu(1,"客户"));
    			   list.add(new  Stu(2,"喝水"));
    			   list.add(new  Stu(3,"地方"));
    			   //将数据放在  var中
    			pageContext.setAttribute(var, list);
    			return SKIP_BODY;
    		}
    }

#### 2.建立tid类 ####

![62d56ecafb5d45d582ff7b291e3b933b.png][]

<tag>
    		<name>dept</name>
    		<tag-class>com.lz.text.Text2</tag-class>
    		
    		<body-content>jsp</body-content>
    		<attribute>
    			<name>var</name>
    			<required>true</required>
    			<rtexprvalue>false</rtexprvalue>
    		</attribute>
    	</tag>

#### 3.实现 ####

![ac370023719b4c059f1cc24993bea07a.png][]

## 三. select标签 ##

### 1.建立实现类 ###

![d3c4b583b6834e1abedaed336f7f1615.png][]

![101fc97a67474f6ea01978bd77f33465.png][]

![09e4872aec514dbb843a7a38e1570a3b.png][]

package com.lz.text;
    
    import java.lang.reflect.Field;
    import java.util.ArrayList;
    import java.util.Iterator;
    import java.util.List;
    
    import javax.servlet.jsp.JspException;
    import javax.servlet.jsp.JspWriter;
    import javax.servlet.jsp.tagext.BodyTagSupport;
    
    import com.sun.org.apache.bcel.internal.generic.RETURN;
    
    public class Text3 extends BodyTagSupport {
    	/**
    	 * select标签
    	 **/
    	private   String  selectVal;	//下拉框
    
    	public Text3(String selectVal) {
    		super();
    		this.selectVal = selectVal;
    	}
    
    	/**
    	 * @return the selectVal
    	 */
    	public String getSelectVal() {
    		return selectVal;
    	}
    
    	/**
    	 * @param selectVal the selectVal to set
    	 */
    	public void setSelectVal(String selectVal) {
    		this.selectVal = selectVal;
    	}
    
    	// 下拉框数据
    	private List<Object> items = new ArrayList<Object>();
    
    	public Text3() {
    		super();
    	}
    
    	public Text3(List<Object> items, String optionval, String optionText) {
    		super();
    		this.items = items;
    		this.optionval = optionval;
    		this.optionText = optionText;
    	}
    
    	/**
    	 * @return the items
    	 */
    	public List<Object> getItems() {
    		return items;
    	}
    
    	/**
    	 * @param items
    	 *            the items to set
    	 */
    	public void setItems(List<Object> items) {
    		this.items = items;
    	}
    
    	/**
    	 * @return the optionval
    	 */
    	public String getOptionval() {
    		return optionval;
    	}
    
    	/**
    	 * @param optionval
    	 *            the optionval to set
    	 */
    	public void setOptionval(String optionval) {
    		this.optionval = optionval;
    	}
    
    	/**
    	 * @return the optionText
    	 */
    	public String getOptionText() {
    		return optionText;
    	}
    
    	/**
    	 * @param optionText
    	 *            the optionText to set
    	 */
    	public void setOptionText(String optionText) {
    		this.optionText = optionText;
    	}
    
    	// 下拉框值
    	private String optionval;
    	// 下拉框标签体内容
    	private String optionText;
    
    	@Override
    	public int doStartTag() throws JspException {
    		// z没有标签提 ，页面需要下拉框值
    		JspWriter out = pageContext.getOut();
    		return super.doStartTag();
    	}
    
    	public    String  toHTML() throws NoSuchFieldException, SecurityException, IllegalArgumentException, Exception {
        // StringBuffer    和 string  区别
    	//string处理字符串更加消耗服务器内存  
    	  StringBuffer   sb=new  StringBuffer("<select>");  
    	  for (Object object : items) {
    		  //取出对象具某个体属性值
    		  String  val=getObjAttrValue(object,optionval);
    		String  text=getObjAttrValue(object,optionval);
    		sb.append("<option "+(val.equals(selectVal)?"selected":"")+" value='"+val+"'>"+text+"</option>");
    	}
    	  sb.append("</select>");
    	  return    sb.toString();
      }
    /**
     *   取出对象具某个体属性值
     * @param object
     * @param  attr  id/name
     * @return
     * @throws SecurityException 
     * @throws NoSuchFieldException 
     * @throws Exception 
     * @throws IllegalArgumentException 
     */
    	private String getObjAttrValue(Object object, String attr) throws NoSuchFieldException, SecurityException, IllegalArgumentException, Exception {
    		Class clz = object.getClass();
    		Field f = clz.getDeclaredField(attr);
    		f.setAccessible(true);
    		return f.get(object).toString();
    	}
    
    
    }

#### 2.建立tid ####

![20705996814f44cd915d32257206fdb9.png][]

<tag>
    		<name>select</name>
    		<tag-class>com.lz.text.Text3</tag-class>
    		
    		<body-content>jsp</body-content>
    		<attribute>
    			<name>items</name>
    			<required>true</required> 
    			<rtexprvalue>true</rtexprvalue>
    		</attribute>
    		<attribute>
    			<name>optionval</name>
    			<required>true</required>
    			<rtexprvalue>true</rtexprvalue>
    		</attribute>
    		<attribute>
    			<name>optionText</name>
    			<required>true</required>
    			<rtexprvalue>true</rtexprvalue>
    		</attribute>
    		<attribute>
    			<name>selectVal</name>
    			<required>true</required>
    			<rtexprvalue>true</rtexprvalue>
    		</attribute>
    		
    		
    	</tag>

#### 3.实现 ####

![a7a16f133e904d82a43ba5687476f809.png][]

[adf47334237a4706a5d5eabc472527b4.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/13c05ab41388486cbc2b4ba79c576bc3.png
[2609efe6f5224b6fbc826f616ca2c935.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/cf217fd7ff51405795c46d6f29f54264.png
[fb98c732ebdd49c6b33aea4bafb3f050.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/47b7fa183ed14b38b8a31ff9bb087fd2.png
[b918be796e5c4b728481186988dbbf65.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/8bade4f89f094260b6b256a9b83f8420.png
[5abdeb961301400dabe2923741b43fe2.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/e8a575ad3abc4584938bf5beb74e9ad1.png
[62d56ecafb5d45d582ff7b291e3b933b.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/ad547fa930154a2f8cec1b1aa3db0e87.png
[ac370023719b4c059f1cc24993bea07a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/e74daaaa11fc4df5908c9b7f65815fb0.png
[d3c4b583b6834e1abedaed336f7f1615.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/8943de7445f54d789a93003c3f7a6248.png
[101fc97a67474f6ea01978bd77f33465.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/173ec25e4fcb43a2a3d8a27a1e3409c2.png
[09e4872aec514dbb843a7a38e1570a3b.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/4e95439c8af7456e945d4a49b725f8db.png
[20705996814f44cd915d32257206fdb9.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/2203196b00a546288c40de0d39e0405d.png
[a7a16f133e904d82a43ba5687476f809.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/b2121c88c362478b861a29b8a722838b.png