JDBC+Servlet+JSP整合開發之27.JSP自定義標籤

–簡介
–標籤接口和類
–標籤的分類
–標籤實例
? HelloWorld 簡單標籤
?有屬性的標籤
?有標籤體，有屬性的標籤
?嵌套標籤
?循環標籤

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? 簡介
–標籤在JSP頁面中被調用
–標籤對應一個Java 處理類，來處理標籤邏輯
–好處是，是頁面中儘可能少寫代碼

? 標籤接口和類
–JSP全部標籤都實現了javax.servlet.jsp.JspTag接口
?這個接口有兩個之間接口：
? SimpleTag
–JSP 2.0 中新增的接口
? Tag
–是一個經典的必須實現的接口
–它有一個直接接口是IterationTag

? 標籤的分類
–不帶屬性和標籤體的簡單標籤
–不帶標籤體，可是有屬性的標籤
–帶標籤體，且有屬性的標籤

? 標籤實例
–HelloWorld 簡單標籤
–有屬性的標籤
–有標籤體，有屬性的標籤
–嵌套標籤
–循環標籤

先來看下如何實現簡單的標籤哈~

MyTag.java

此類實現了Tag接口

 

MyTag.tld

MyTag.jsp

測試：

下面咱們繼承TagSupport抽象類，這樣更簡單一些哈~

MyTag2.java

MyTag.tld

MyTag2.jsp

測試：

下面咱們輸出一個下拉列表哈~

MyTag3.java

MyTag.tld

MyTag.jsp

測試：

 

下面從數據庫取出下拉列表內容，並將其定義爲標籤。

 

MyTag.tld

MyTag.jsp

MyTag4.java

PositionService.java

ConnectionUtil.java

package com.michael.tag;    

import java.sql.Connection;    
import java.sql.DriverManager;    
import java.util.Properties;    

public class ConnectionUtil {    

         /**    
         * @param args    
         */    
         public static void main(String[] args) {    
                ConnectionUtil cu = new ConnectionUtil();    
                System.out.println(cu.openConnection());    
        }    
         public Connection openConnection() {    
                String url = "";    
                String driver = "";    
                String user = "";    
                String password = "";    
                Properties prop = new Properties();    
                 try {    
                        prop.load( this.getClass().getClassLoader().getResourceAsStream( "DBConfig.properties"));    
                        driver = prop.getProperty( "driver");    
                        url = prop.getProperty( "url");    
                        user = prop.getProperty( "user");    
                        password = prop.getProperty( "password");    
                        Class.forName(driver);    
                        Connection conn = DriverManager.getConnection(    
                                        url, user, password);    
                         return conn;    
                } catch (Exception e) {    
                        e.printStackTrace();    
                }    
                 return null;    
        }    
         public Connection getConnection(String driver, String url, String user,    
                        String password) {    
                 // Class.forName()    
                 try {    
                        Class.forName(driver);    
                         // DriverManager get connection    
                        Connection conn = DriverManager.getConnection(url, user, password);    
                         return conn;    
                } catch (Exception e) {    
                        e.printStackTrace();    
                }    
                 return null;    
        }    

         public Connection getConnection() {    
                 // Class.forName()    
                 try {    
                        Class.forName( "com.mysql.jdbc.Driver");    
                         // DriverManager get connection    
                        Connection conn = DriverManager.getConnection(    
                                         "jdbc:mysql://localhost:3306/jsp_db", "root", "963963");    
                        return conn;    
                } catch (Exception e) {    
                        e.printStackTrace();    
                }    
                return null;    
        }    

}

Position.java

DBConfig.properties

測試：

數據庫中有四條記錄，咱們看下能不能取出來哈~

下面咱們在數據庫中增長一條記錄測試一下哈~

 

 

以上四個標籤都是沒有屬性的，下面咱們測試有屬性的標籤，傳遞一個參數，循環的輸出哈~

MyTag5.java

MyTag.tld

MyTag.jsp

測試：

下面測試有標籤體的標籤，咱們能夠實現一個接口或者繼承一個類哈~

先看實現接口的方法

MyTag6.java

package com.michael.tag;    

import java.io.IOException;    

import javax.servlet.jsp.JspException;    
import javax.servlet.jsp.PageContext;    
import javax.servlet.jsp.tagext.BodyContent;    
import javax.servlet.jsp.tagext.BodyTag;    
import javax.servlet.jsp.tagext.Tag;    

public class MyTag6 implements BodyTag{    
         private int count;    
         private BodyContent bodyContent;    
         public void setCount( int count) {    
                 this.count = count;    
        }    
         public void doInitBody() throws JspException {    
        }    

         public void setBodyContent(BodyContent bodyContent) {    
                 this.bodyContent = bodyContent;    
        }    

         public int doAfterBody() throws JspException {    
                 if(count>1){    
                        count--;    
                         return this.EVAL_BODY_AGAIN;    
                }    
                 return this.SKIP_BODY;    
        }    

         public int doEndTag() throws JspException {    
                 try {    
                         if(bodyContent!= null)    
                        bodyContent.print(bodyContent.getEnclosingWriter());    
                } catch (IOException e) {    
                        e.printStackTrace();    
                }    
                 return this.EVAL_PAGE;    
        }    

         public int doStartTag() throws JspException {    
                 if(count>0){    
                         return this.EVAL_BODY_INCLUDE;    
                }    
                 return this.SKIP_BODY;    
        }    

         public Tag getParent() {    
                 return null;    
        }    

         public void release() {    
        }    

         public void setPageContext(PageContext pageContext) {    
        }    

         public void setParent(Tag tag) {    
        }    
}

MyTag.tld

MyTag.jsp

測試：

下面咱們實現抽象類來測試有標籤體的標籤哈~

MyTag7.java

MyTag.tld

MyTag.jsp

測試：

在JSP2.0中還有一個新特徵，具備SimpleTag接口，還有針對這個接口的實現類，若是使用這個接口就更方法了哈~

MyTag8.java

MyTag.tld

MyTag.jsp

測試：

下面咱們實現針對這個接口的抽象類

MyTag9.java

MyTag.tld

MyTag.jsp

測試：

 

 

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