velocity 的 escape实现

EscapeHtmlReference的escape方法调用以下方法实现：

StringEscapeUtils.escapeHtml(param);  再调用

org.apache.commons.lang.Entities.HTML40.escape(writer, string);
代码如下：

public void escape(Writer writer, String str) throws IOException {
    int len = str.length();

    for(int i = 0; i < len; ++i) {
        char c = str.charAt(i);
        String entityName = this.entityName(c);
        if(entityName == null) {
            if(c > 127) {
                writer.write("&#");
                writer.write(Integer.toString(c, 10));
                writer.write(59);   //就是个分号
            } else {
                writer.write(c);
            }
        } else {
            writer.write(38);
            writer.write(entityName);
            writer.write(59);
        }
    }

}

我们也可以自己调用

StringEscapeUtils.escapeHtml(param);
比如：

String param = request.getParameter("p");
String x = StringEscapeUtils.escapeHtml(param);
System.out.println(x);

输入 <script>alert(/xxx/)</script>  输出 &lt;script&gt;alert(/xxx/)&lt;/script&gt;

velocity 也可以自定义 EventHandler 处理xss，配置EscapeHtmlReference 替换成自己的EventHandler 

<bean id="velocityConfigurer"
      class="org.springframework.web.servlet.view.velocity.VelocityConfigurer">
    <property name="resourceLoaderPath" value="/WEB-INF/pages/"/>
    <property name="velocityProperties">
        <props>
            <prop key="input.encoding">utf-8</prop>
            <prop key="output.encoding">utf-8</prop>
            <prop key="eventhandler.referenceinsertion.class">org.apache.velocity.app.event.implement.EscapeHtmlReference</prop>
            <prop key="eventhandler.escape.html.match">/^(?!\$\!?unesc_).*/</prop>
        </props>
    </property>
</bean>