logback的UNDEFINED_PROPERTY屬性源碼執(zhí)行流程解讀

更新時(shí)間：2023年11月07日 10:00:37 作者：codecraft

這篇文章主要為大家介紹了logback的UNDEFINED_PROPERTY屬性源碼執(zhí)行流程解讀,有需要的朋友可以借鑒參考下,希望能夠有所幫助,祝大家多多進(jìn)步,早日升職加薪

序

本文主要研究一下logback的UNDEFINED_PROPERTY

substVars

ch/qos/logback/core/util/OptionHelper.java

public static String substVars(String input, PropertyContainer pc0, PropertyContainer pc1) {
        try {
            return NodeToStringTransformer.substituteVariable(input, pc0, pc1);
        } catch (ScanException e) {
            throw new IllegalArgumentException("Failed to parse input [" + input + "]", e);
        }
    }

OptionHelper提供了substVars方法，它執(zhí)行NodeToStringTransformer的substituteVariable方法

substituteVariable

ch/qos/logback/core/subst/NodeToStringTransformer.java

public static String substituteVariable(String input, PropertyContainer pc0, PropertyContainer pc1) throws ScanException {
        Node node = tokenizeAndParseString(input);
        NodeToStringTransformer nodeToStringTransformer = new NodeToStringTransformer(node, pc0, pc1);
        return nodeToStringTransformer.transform();
    }

substituteVariable方法則先根據(jù)input解析node，再創(chuàng)建NodeToStringTransformer，執(zhí)行其transform方法

transform

ch/qos/logback/core/subst/NodeToStringTransformer.java

public String transform() throws ScanException {
        StringBuilder stringBuilder = new StringBuilder();
        compileNode(node, stringBuilder, new Stack<Node>());
        return stringBuilder.toString();
    }

transform方法主要是執(zhí)行compileNode，通過(guò)stringBuilder來(lái)收集變量值

compileNode

ch/qos/logback/core/subst/NodeToStringTransformer.java

private void compileNode(Node inputNode, StringBuilder stringBuilder, Stack<Node> cycleCheckStack) throws ScanException {
        Node n = inputNode;
        while (n != null) {
            switch (n.type) {
            case LITERAL:
                handleLiteral(n, stringBuilder);
                break;
            case VARIABLE:
                handleVariable(n, stringBuilder, cycleCheckStack);
                break;
            }
            n = n.next;
        }
    }

compileNode方法針對(duì)VARIABLE類(lèi)型的執(zhí)行handleVariable方法

handleVariable

ch/qos/logback/core/subst/NodeToStringTransformer.java

private void handleVariable(Node n, StringBuilder stringBuilder, Stack<Node> cycleCheckStack) throws ScanException {
        // Check for recursion
        if (haveVisitedNodeAlready(n, cycleCheckStack)) {
            cycleCheckStack.push(n);
            String error = constructRecursionErrorMessage(cycleCheckStack);
            throw new IllegalArgumentException(error);
        }
        cycleCheckStack.push(n);
        StringBuilder keyBuffer = new StringBuilder();
        Node payload = (Node) n.payload;
        compileNode(payload, keyBuffer, cycleCheckStack);
        String key = keyBuffer.toString();
        String value = lookupKey(key);
        // empty values are considered valid
        if (value != null) {
            Node innerNode = tokenizeAndParseString(value);
            compileNode(innerNode, stringBuilder, cycleCheckStack);
            cycleCheckStack.pop();
            return;
        }
        // empty default literal is a valid value
        if (n.defaultPart == null) {
            stringBuilder.append(key + CoreConstants.UNDEFINED_PROPERTY_SUFFIX);
            cycleCheckStack.pop();
            return;
        }
        Node defaultPart = (Node) n.defaultPart;
        StringBuilder defaultPartBuffer = new StringBuilder();
        compileNode(defaultPart, defaultPartBuffer, cycleCheckStack);
        cycleCheckStack.pop();
        String defaultVal = defaultPartBuffer.toString();
        stringBuilder.append(defaultVal);
    }

handleVariable方法對(duì)于value為null，且defaultValue也為null的設(shè)置了默認(rèn)值為key + CoreConstants.UNDEFINED_PROPERTY_SUFFIX)

UNDEFINED_PROPERTY_SUFFIX

public class CoreConstants {
    //......
    public static final String UNDEFINED_PROPERTY_SUFFIX = "_IS_UNDEFINED";
}

UNDEFINED_PROPERTY_SUFFIX的值為_(kāi)IS_UNDEFINED

小結(jié)

logback通過(guò)NodeToStringTransformer的handleVariable來(lái)獲取變量值，若該value為null，且defaultValue也為null的設(shè)置了默認(rèn)值為key + CoreConstants.UNDEFINED_PROPERTY_SUFFIX)，即key_IS_UNDEFINED，注意這里如果defaultValue不為null則不走IS_UNDEFINED的邏輯，即空字符串也是可以的。對(duì)于自定義appender需要注意一下appender屬性的value處理邏輯。

以上就是logback的UNDEFINED_PROPERTY屬性源碼執(zhí)行流程解讀的詳細(xì)內(nèi)容，更多關(guān)于logback UNDEFINED_PROPERTY的資料請(qǐng)關(guān)注腳本之家其它相關(guān)文章！

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