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JSP自定义tag

时间:2016-08-18 23:19:40      阅读:263      评论:0      收藏:0      [点我收藏+]

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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‘)}

 

 

reference:

http://www.runoob.com/jsp/jsp-custom-tags.html

https://www.ibm.com/developerworks/cn/java/j-lo-jsp2tag/

 

JSP自定义tag

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原文地址:http://www.cnblogs.com/woshimrf/p/5779918.html

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