About JSP The benefits of labels are no longer wordy
The data dictionary is the drop-down box used , As long as you define which dictionary to use, the available contents of this dictionary will be displayed
When displaying a dictionary, you can display the displayed value of the dictionary by defining the dictionary and attribute value
First, in the web.xml Define the reference of custom label loading in , The two attributes are referenced URI And load path
<?xml version="1.0" encoding="UTF-8"?><web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"> <welcome-file-list> <welcome-file>index.jsp</welcome-file> </welcome-file-list> <jsp-config> <taglib> <taglib-uri>/tld/web-html</taglib-uri> <taglib-location> /WEB-INF/tlds/web-html.tld </taglib-location> </taglib> </jsp-config></web-app>
stay web-html.tld Define your own label in , For data dictionary application, we need a tag library , Three labels . Namely ,select label ,options label , And the label of the real data dictionary , Each tag corresponds to a different implementation class
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN" "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd"><taglib> <tlib-version>1.0</tlib-version><!-- Tag library version --> <jsp-version>1.2</jsp-version> <!-- Required by the tag library JSP Specification version --> <short-name>html</short-name> <!-- JSP Page authoring tools can be used to create optional names for helpers --> <tag> <name>select</name> <tag-class>com.SelectTag</tag-class> <body-content>JSP</body-content> <attribute> <name>name</name> <rtexprvalue>true</rtexprvalue> </attribute> <attribute> <name>style</name> <rtexprvalue>true</rtexprvalue> </attribute> </tag> <tag> <name>options</name> <tag-class>com.OptionsTag</tag-class> <body-content>JSP</body-content> <attribute> <name>collection</name> <rtexprvalue>true</rtexprvalue> </attribute> </tag> <tag> <name>selectDisplay</name> <tag-class>com.SelectDisplay</tag-class> <body-content>JSP</body-content> <attribute> <name>collection</name> <rtexprvalue>true</rtexprvalue> </attribute> <attribute> <name>name</name> <rtexprvalue>true</rtexprvalue> </attribute> <attribute> <name>value</name> <rtexprvalue>true</rtexprvalue> </attribute> </tag></taglib>
Implementation class
The function of the implementation class is to splice the required in the background HTML Label content , Then from JSP For the output
The two main methods of implementing classes , When one encounters this tag, it outputs , One is output at the end
If you need to define attributes , You can refer to the implementation class to define attributes , And in TLD In the definition of , stay JSP When using the tag in, the shortcut key can show this attribute
First of all select Code of label ：
package com;import java.io.IOException;import javax.servlet.jsp.JspException;import javax.servlet.jsp.JspTagException;import javax.servlet.jsp.tagext.BodyTagSupport;/** * TagSupport And BodyTagSupport The difference between : * It mainly depends on whether the label processing class wants to read the content of the label body and change the content returned by the label body , Use it if you don't need it TagSupport, Otherwise it will be used. BodyTagSupport * use TagSupport Implemented tags , Both can be used. BodyTagSupport To achieve , because BodyTagSupport Inherited TagSupport */@SuppressWarnings("serial")public class SelectTag extends BodyTagSupport { @Override public int doStartTag() throws JspException { try { StringBuffer results = new StringBuffer("<select"); if(name != null){ results.append(" name=\""); results.append(name); results.append("\""); } if(style != null){ results.append(" style=\""); results.append(style); results.append("\""); } results.append(">"); pageContext.getOut().write(results.toString()); } catch (IOException ex) { throw new JspTagException(" error "); } return EVAL_BODY_INCLUDE; } @Override public int doEndTag() throws JspException { try { StringBuffer results = new StringBuffer(""); // Because the drop-down contains drop-down content , So you can only write when you encounter the end tag select end results.append("</select>"); pageContext.getOut().write(results.toString()); } catch (IOException ex) { throw new JspTagException(" error "); } return EVAL_PAGE; } // style protected String style; // name protected String name; public String getStyle() { return style; } public void setStyle(String style) { this.style = style; } public String getName() { return name; } public void setName(String name) { this.name = name; } /** doStartTag() Method is the method that will be called at the beginning of the tag , Its legal return value is EVAL_BODY_INCLUDE And SKIP_BODY, The former indicates that the text between labels will be displayed , The latter means that the text between labels is not displayed doEndTag() Method is the method called at the end of the tag , Its legal return value is EVAL_PAGE And SKIP_PAGE, The former means that after processing the label, continue to execute the following JSP Webpage , The latter means not to process the following JSP Webpage doAfterBody(), This method is called after displaying the text between tags , The return values are EVAL_BODY_AGAIN And SKIP_BODY, The former will display the text between labels again , The latter proceeds to the next step of label processing EVAL_BODY_INCLUDE： hold Body Read into the existing output stream ,doStartTag() Functions are available EVAL_PAGE： Continue processing the page ,doEndTag() Functions are available SKIP_BODY： Ignore right Body To deal with ,doStartTag() and doAfterBody() Functions are available SKIP_PAGE： Ignore the processing of the remaining pages ,doEndTag() Functions are available EVAL_BODY_BUFFERED： Request buffer , from setBodyContent() Function to get BodyContent Object to handle tag Of body, If the class implements BodyTag, that doStartTag() You can use , Otherwise it's illegal EVAL_BODY_AGAIN： Request to continue processing body, Return from doAfterBody(), This return value is in the loop you make tag It is very useful when The predetermined processing order is ：doStartTag() return SKIP_BODY,doAfterBodyTag() return SKIP_BODY,doEndTag() return EVAL_PAGE If inherited TagSupport after , If there is no way to rewrite , The execution order of label processing is ：doStartTag() -> Don't show text ->doEndTag()-> Execute the next page If you rewrite doStartTag(), The return value must be specified , If you specify EVAL_BODY_INCLUDE, Then the order of execution is ：doStartTag()-> According to the text ->doAfterBodyTag()->doEndTag()-> Execute the following page */}
About return parameters , You can also return specific numbers , Don't worry too much
Then there is the drop-down content implementation class
package com;import java.io.IOException;import javax.servlet.jsp.JspException;import javax.servlet.jsp.JspTagException;import javax.servlet.jsp.tagext.BodyTagSupport;@SuppressWarnings("serial")public class OptionsTag extends BodyTagSupport { @Override public int doStartTag() throws JspException { return EVAL_BODY_INCLUDE; } @Override public int doEndTag() throws JspException { try { StringBuffer results = new StringBuffer(""); if ("SEX".equals(collection)) { results.append("<option value=\"0\" selected=\"selected\"> Please select </option>"); results.append("<option value=\"1\"> male </option>"); results.append("<option value=\"2\"> Woman </option>"); } pageContext.getOut().write(results.toString()); } catch (IOException ex) { throw new JspTagException(" error "); } return EVAL_PAGE; } // collection Just pass a logo , Whether the specific drop-down value content is obtained from the database or from the request is a different specific implementation protected String collection; public String getCollection() { return collection; } public void setCollection(String collection) { this.collection = collection; }}
How to store and query your dictionary data from the database , You can customize the implementation
Displayed label implementation , In order to get the tag content value on the page in the future , We define hidden fields to store attribute values , Then display the content
package com;import java.io.IOException;import javax.servlet.jsp.JspException;import javax.servlet.jsp.JspTagException;import javax.servlet.jsp.tagext.BodyTagSupport;@SuppressWarnings("serial")public class SelectDisplay extends BodyTagSupport { @Override public int doStartTag() throws JspException { try { StringBuffer results = new StringBuffer(""); pageContext.getOut().write(results.toString()); } catch (IOException ex) { throw new JspTagException(" error "); } return EVAL_BODY_INCLUDE; } @Override public int doEndTag() throws JspException { try { StringBuffer results = new StringBuffer(""); if ("SEX".equals(collection)) { results.append("<span>"); results.append("<input type=\""); results.append("hidden\" name=\""); results.append(getName()); results.append("\""); results.append(" value=\""); results.append(getValue()); results.append("\">"); if ("1".equals(getValue())) { results.append(" male "); } else if ("2".equals(getValue())) { results.append(" Woman "); } else { results.append(" Please select "); } results.append("</span>"); } pageContext.getOut().write(results.toString()); } catch (IOException ex) { throw new JspTagException(" error "); } return EVAL_PAGE; } // collection Just pass a logo , Whether the specific drop-down value content is obtained from the database or from the request is a different specific implementation protected String collection; // Value delivered protected String value; // Name of the attribute protected String name; public String getCollection() { return collection; } public void setCollection(String collection) { this.collection = collection; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getValue() { return value; } public void setValue(String value) { this.value = value; }}
JSP I quote , Directly in index.jsp I quote
The corresponding label content needs to be introduced , The way of introduction is JSP Head quote
The properties of the tag can be set or not , The use of labels and HTML The use of labels is the same , Define attributes
<%@ page language="java" pageEncoding="UTF-8"%><%@ taglib uri="/tld/web-html" prefix="html"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <title>JSP Implementation of custom label </title> </head> <body> Please select ： <html:select name="sex" style="width:100px"> <html:options collection="SEX"></html:options> </html:select> Show gender ： <html:selectDisplay collection="SEX" value="1" name="sex"></html:selectDisplay> </body></html>
The latter
Visit the project to see the effect
If you want to design a large tag library by yourself , You can design a parent class , Contains some main properties , for example name,id,style Equal attribute . Then define your own unique attributes in subclasses
This implementation is just for learning JSP Custom labels are used HelloWorld Program , Then it includes practical examples of dictionary application , The procedure is simple , For reference only
I recommend you to read more about “ jsp Custom tag The data dictionary ” The article
