velocity自定义指令不生效问题解决之旅

一、背景现象

为了支持灵活的、可自定义的脱敏规则，工程拟采用velocity实现该目的，为此，自定义了：

• mask、substr两个指令，其中
• mask实现

public class MaskDirective extends Directive {

    @Override
    public String getName() {
        return "mask";
    }

    @Override
    public int getType() {
        return LINE;
    }

    @Override
    public boolean render(InternalContextAdapter ctx, Writer writer, Node node) throws IOException, ResourceNotFoundException, ParseErrorException, MethodInvocationException {

        //fieldName
        SimpleNode snField = (SimpleNode) node.jjtGetChild(0);

        String maskChar = (String)snField.value(ctx);

        snField = (SimpleNode) node.jjtGetChild(1);
        int count = (int)snField.value(ctx);

        StringBuilder buff = new StringBuilder();

        for(int i = 0; i < count; i++) {
            buff.append(maskChar);
        }

        writer.write(buff.toString());

        return true;

    }
}

• substr实现

public class SubstrDirective extends Directive {

    @Override
    public String getName() {
        return "substr";
    }

    @Override
    public int getType() {
        return LINE;
    }

    @Override
    public boolean render(InternalContextAdapter ctx, Writer writer, Node node) throws IOException, ResourceNotFoundException, ParseErrorException, MethodInvocationException {

        //fieldName
        SimpleNode snField = (SimpleNode) node.jjtGetChild(0);

        String fieldValue = (String)snField.value(ctx);

        if(fieldValue == null || fieldValue.length() == 0){
            return false;
        }

        int items = node.jjtGetNumChildren();

        int startIdx = Integer.MIN_VALUE;
        int endIdx = fieldValue.length();

        if(items < 1){
            return false;
        }

        try{

            snField = (SimpleNode) node.jjtGetChild(1);
            startIdx = (int)snField.value(ctx);

            if(items > 2){
                snField = (SimpleNode) node.jjtGetChild(2);
                endIdx = (int)snField.value(ctx);

                if(endIdx > fieldValue.length()){
                    endIdx = fieldValue.length();
                }

            }

            if(startIdx >= endIdx){
                return false;
            }

            StringBuilder buff = new StringBuilder();

            if(items > 2){
                writer.write(fieldValue.substring(startIdx,endIdx));
            }else{

                if(startIdx <  0){
                    startIdx = startIdx + fieldValue.length();
                }

                writer.write(fieldValue.substring(startIdx));
            }

            return true;

        }catch(Exception e){
            return false;
        }
    }
}

• velocity初始化方法：

public final class VelocityHelper {

    private Set<String> userExtDirective ;
    private final static String K_USERDIRECTIVE = "userdirective";

    private final static VelocityHelper VH = new VelocityHelper();
   private VelocityHelper(){

    }

    public static final VelocityHelper getInstance(){
        return VH;
    }

    /**
     * 初始化
     */
    public void init() throws Exception{

        Properties prop = new Properties();

        StringBuilder buff = new StringBuilder();

        for(String s : userExtDirective){
            buff.append(s.trim()).append(",");
        }

        LogHelper.trace("start VelocityHelper.init[" + buff.toString() + "]");

        prop.setProperty(K_USERDIRECTIVE, buff.toString().substring(0, buff.length()-1));
        Velocity.init(prop);

        LogHelper.trace("end VelocityHelper.init");

    }

    /**
     * 根据报文模板和<code>VelocityContext</code>，渲染出实际的业务报文
     *
     * @param context 业务上下文信息
     * @param template 模板
     * @return
     * @throws IOException
     */
    public String evaluate(String template, final VelocityContext context) throws IOException {
        Writer writer = new StringWriter();
        try {
            Velocity.evaluate(context, writer, StringUtil.EMPTY_STRING, template);
            return writer.toString();
        } finally {
            IOUtils.closeQuietly(writer);
        }
    }

    /**
     *
     * @param userExtDirective
     *
     */
    public void setUserExtDirective(Set<String> userExtDirective){

        this.userExtDirective = userExtDirective;
    }

}

部署到服务器后，以下表达式始终未得到替换：#substr($maskField, 0, 3)#mask('*', 4)#substr($maskField, -4) 

二、原因分析

开始怀疑是配置等问题，经过以下方法尝试均为解决问题：

1、怀疑spring xml配置问题----未解决

2、硬编码指令，在构造函数塞入指令----未解决

无奈，登录服务器grep velocity 得到了以下的输出（其中之一），茅塞顿开。

2019-02-02 07:49:52,315 [  - /// - ] INFO  assemble.VMRender - resource=class path resource [velocity/velocity.properties]

Velocity.ini及Velocity.evalute均是全局单一模式，既然有人捷足先登，自然不在做第二次初始化。

三、解决方案

采用VelocityEngine替换Velocity，实现jar包间隔离，独立管理自己的资源。

private VelocityEngine velocityEngine = null;
velocityEngine = new VelocityEngine(prop);
velocityEngine.evaluate(context, writer, StringUtil.EMPTY_STRING, template);