S2-001 调试分析

public void validate() {
    if (username == null || username.trim().equals("")) {
        addFieldError("username", "UserName is required");
    }
    if (phoneNumber == null || phoneNumber.trim().equals("")) {
        addFieldError("phoneNumber", "PhoneNumber is required");
    }
}

// xwork-2.0.1.jar!/com/opensymphony/xwork2/interceptor/DefaultWorkflowInterceptor.class
... snip ...
// 是否验证失败
if(validationAwareAction1.hasErrors()) {
    if(_log.isDebugEnabled()) {
        _log.debug("Errors on action " + validationAwareAction1 + ", returning result name \'input\'");
    }

    return this.inputResultName;
}

// struts2-core-2.0.6.jar!/org/apache/struts2/views/jsp/ComponentTagSupport.class
public int doEndTag() throws JspException {
    this.component.end(this.pageContext.getOut(), this.getBody());
    this.component = null;
    return 6;
}

public int doStartTag() throws JspException {
    this.component = this.getBean(this.getStack(), (HttpServletRequest)this.pageContext.getRequest(), (HttpServletResponse)this.pageContext.getResponse());
    Container container = Dispatcher.getInstance().getContainer();
    container.inject(this.component);
    this.populateParams();
    boolean evalBody = this.component.start(this.pageContext.getOut());
    return evalBody?(this.component.usesBody()?2:1):0;
}

// struts2-core-2.0.6.jar!/org/apache/struts2/components/UIBean.class
public boolean end(Writer writer, String body) {
    this.evaluateParams();	// 遍历标签属性

    try {
        super.end(writer, body, false);
        this.mergeTemplate(writer, this.buildTemplateName(this.template, this.getDefaultTemplate()));
    } catch (Exception var7) {
        LOG.error("error when rendering", var7);
    } finally {
        this.popComponentStack();
    }

    return false;
}

public void evaluateParams() {
    ... snip ...
    if(this.name != null) {
        name = this.findString(this.name);  // 查询标签 name
        this.addParameter("name", name);
    }

    // 添加标签值至参数列表，供错误页面显示
    if(this.parameters.containsKey("value")) {
        this.parameters.put("nameValue", this.parameters.get("value"));
    } else if(this.evaluateNameValue()) {   // 是否取出标签的值，函数返回 true
        Class form = this.getValueClassType();
        if(form != null) {
            if(this.value != null) {
                this.addParameter("nameValue", this.findValue(this.value, form));
            } else if(name != null) {
                String tooltipConfigMap = name;
                if(this.altSyntax()) {  // 若开启 altSyntax，拼接查询语句
                                        // altSyntax 属性指定是否允许在 Struts2 标签中使用表达式语法，默认值是true
                    tooltipConfigMap = "%{" + name + "}";
                }

                this.addParameter("nameValue", this.findValue(tooltipConfigMap, form)); // 查询并添加结果至参数列表
                                                                                        // 查询语句为 %{name}
            }
        } else if(this.value != null) {
            this.addParameter("nameValue", this.findValue(this.value));
        } else if(name != null) {
            this.addParameter("nameValue", this.findValue(name));
        }
    }
... snip ...
}

// struts2-core-2.0.6.jar!/org/apache/struts2/components/Component.class
protected Object findValue(String expr, Class toType) {
    if(this.altSyntax() && toType == String.class) {    // 若开启 altSyntax 进入 TextParseUtil.translateVariables，
                                                        // 对表达式进行解析
        return TextParseUtil.translateVariables('%', expr, this.stack);
    } else {
        if(this.altSyntax() && expr.startsWith("%{") && expr.endsWith("}")) {
            expr = expr.substring(2, expr.length() - 1);
        }

        return this.getStack().findValue(expr, toType);
    }
}

// xwork-2.0.1.jar!/com/opensymphony/xwork2/util/TextParseUtil.class
public static Object translateVariables(char open, String expression, ValueStack stack, Class asType, TextParseUtil.ParsedValueEvaluator evaluator) {
    Object result = expression; // 表达式，%{name}

    while(true) {
        int start = expression.indexOf(open + "{");
        int length = expression.length();
        int x = start + 2;
        int count = 1;

        // 匹配 %{key}
        while(start != -1 && x < length && count != 0) {
            char c = expression.charAt(x++);
            if(c == 123) {
                ++count;
            } else if(c == 125) {
                --count;
            }
        }

        int end = x - 1;
        if(start == -1 || end == -1 || count != 0) {
            return XWorkConverter.getInstance().convertValue(stack.getContext(), result, asType);
        }

        // 提取表达式 %{name} => name
        String var = expression.substring(start + 2, end);
        Object o = stack.findValue(var, asType);    // 取得标签值 o
                                                    // 进入 OGNL!
        if(evaluator != null) {
            o = evaluator.evaluate(o);
        }

        String left = expression.substring(0, start);
        String right = expression.substring(end + 1);
        // o 存在，这里为 Payload %{1+1}
        // 递归解析表达式，也就是说最终 Payload 将变为 1+1，进入 OGNL 最终得以执行！
        if(o != null) {
            if(TextUtils.stringSet(left)) {
                result = left + o;
            } else {
                result = o;
            }

            if(TextUtils.stringSet(right)) {
                result = result + right;
            }

            expression = left + o + right;
        } else {
            result = left + right;
            expression = left + right;
        }
    }
}