JSP自定义tag
前端需要调用后端的配置，想起velocity-tools。然而jsp的话，目前只能想到tag和EL表达式了。
Tag相当好写，jsp2.0提供了简化写法：
编写一个java类：
public class HelloWorldTag extends SimpleTagSupport {
public void doTag() throws JspException, IOException{
JspWriter out = getJspContext().getOut();
out.println("Hello Custom Tag!");
}
}然后编写对应tld：
<?xml version="1.0" encoding="UTF-8"?>
<taglib 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 [url]http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd[/url]"
version="2.0">
<tlib-version>1.0</tlib-version>
<short-name>Example TLD</short-name>
<tag>
<name>hello</name>
<tag-class>com.test.demo.HelloWorldTag</tag-class>
<body-content>empty</body-content>
</tag>
</taglib>然后就可以在页面上使用了：
<%@ taglib prefix="ex" uri="/WEB-INF/hello.tld" %><ex:hello/>上述是没有body的tag，如果想要输出body的内容：
新写一个java类：
public class BodyTag extends SimpleTagSupport {
StringWriter sw = new StringWriter();
public void doTag() throws JspException, IOException{
getJspBody().invoke(sw);
JspWriter out = getJspContext().getOut();
out.println(sw.toString());
}
}在原来tld文件里面追加一个tag：
<tag>
<name>body</name>
<tag-class>com.test.demo.BodyTag</tag-class>
<body-content>scriptless</body-content>
</tag>在页面上：
<ex:body>
This is message body.
</ex:body>如果想要在tag上追加参数：
public class StandardTag extends SimpleTagSupport {
private String message;
public void setMessage(String message) {
this.message = message;
}
StringWriter sw = new StringWriter();
public void doTag() throws JspException, IOException{
JspWriter out = getJspContext().getOut();
if (message!=null){
//from filed
out.println(message);
}else{
//from body
getJspBody().invoke(sw);
out.println(sw.toString());
}
}
}在tld中添加一个新tag:
<tag>
<name>msg</name>
<tag-class>com.test.demo.StandardTag</tag-class>
<body-content>scriptless</body-content>
<attribute>
<name>message</name>
<required>false</required>
<type>java.lang.String</type>
</attribute>
</tag>在页面上使用：
<ex:msg message="show message from para">
</ex:msg>
---------------
<ex:msg>
if message==null , then show body.
</ex:msg>如果想要使用传参，使用EL表达：
在java类中添加一个static方法：
public static String hello(String name){
return "Welcome: " + name;
}然后在tld中添加：
<function>
<name>welcome</name>
<function-class>com.test.demo.StandardTag</function-class>
<function-signature>java.lang.String hello(java.lang.String)</function-signature>
<example>${ex:welcome('Ryan')}</example>
</function>然后页面上调用：
${ex:welcome('Leslie')}在spring mvc 中，有个很好用的tag支持类RequestContextAwareTag，下面做一个简单的使用：
public abstract class BaseTag extends RequestContextAwareTag {
private static final EPCLogger LOGGER = EPCLogger.getLogger(BaseTag.class);
private static final long serialVersionUID = -6258930875039222435L;
private BeanUtils beanUtils = new BeanUtils();
private HandlebarUtils handlebarUtils = new HandlebarUtils();
public abstract Object getModel();
public BaseTag() {
}
public void renderHandlebarsView(String templateLocation) {
try {
Template e = this.handlebarUtils.compile(templateLocation);
e.apply(this.getModel(), this.pageContext.getOut());
} catch (Exception var3) {
LOGGER.error(UITagsSystemEvent.BASE_TAG_ERROR, "Error occurred while rendering handlebars view.", var3);
}
}
public Object getBean(String beanName) {
Validate.notNull(beanName);
return this.beanUtils.getBean(this.getRequestContext(), beanName);
}
}public class BeanUtils {
public BeanUtils() {
}
public Object getBean(RequestContext requestContext, String beanName) {
return requestContext.getWebApplicationContext().getBean(beanName);
}
}reference：
http://www.runoob.com/jsp/jsp-custom-tags.html
https://www.ibm.com/developerworks/cn/java/j-lo-jsp2tag/
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