自定义标签——带属性的标签
带属性的标签
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步骤：
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- 创建标签类；
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- 配置标签；
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- 设置标签属性，并使用：
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示例代码：
package taglibclass;
import java.io.Writer;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;
public class QueryTag extends SimpleTagSupport {
private String driver;
private String username;
private String password;
private String url;
private String sql;
private Connection connection = null;
private PreparedStatement ps = null;
private ResultSet rs = null;
private ResultSetMetaData rsmd = null;
public void doTag() {
try {
Class.forName(driver);
connection = DriverManager.getConnection(url, username, password);
ps = connection.prepareStatement(sql);
rs = ps.executeQuery();
rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();
Writer out = getJspContext().getOut();
out.write("<table border='1' width='400px'>");
while (rs.next()) {
out.write("<tr>");
for (int j = 1; j <= columnCount; j++) {
out.write("<td>");
out.write(rs.getString(j));
out.write("</td>");
}
out.write("</tr>");
}
out.write("</table>");
} catch (Exception e) {
e.printStackTrace();
try {
throw new JspException("自定义标签错误" + e.getMessage());
} catch (JspException e1) {
e1.printStackTrace();
}
} finally {
try{
if(rs != null)
rs.close();
if(ps != null)
ps.close();
if(connection != null)
connection.close();
} catch(Exception e) {
e.printStackTrace();
}
}
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public String getSql() {
return sql;
}
public void setSql(String sql) {
this.sql = sql;
}
public String getDriver() {
return driver;
}
public void setDriver(String driver) {
this.driver = driver;
}
}
- 自定义标签配置：
<tag>
<name>paramTag</name>
<tag-class>taglibclass.QueryTag</tag-class>
<!--设定自定义标签体为空，无此参数会抛出异常-->
<body-content>empty</body-content>
<!--设定自定义标签属性-->
<attribute>
<!--设定自定义标签属性名-->
<name>driver</name>
<!--设定自定义标签属性是否强制要求-->
<required>true</required>
<!--设定自定义标签属性是否支持JSP脚本-->
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>url</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>username</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>password</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>sql</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
- 标签设置参数，并使用：
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ taglib uri="mytaglib/mytag" prefix="mytag" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<mytag:paramTag
driver="com.mysql.jdbc.Driver"
url="jdbc:mysql://localhost:3306/userlogin?useUnicode=true&characterEncoding=UTF-8&useSSL=false"
username="root"
password="root"
sql="select * from user"/><br/>
</body>
</html>
