背景
不管是單體應用還是海量應用,都是從小應用開始慢慢演進。當應用逐漸變大,業務邏輯變得更加複雜之後,系統開始變得不穩定,這時候你需要將系統拆分,或者重構。但改造的成本是相對高昂的,這時候你需要考慮的是人力、物力、時間等等。如果系統還沒有到無可救藥的地步(還能跑),簡單的查錯打印日誌是再好不過的了。打印日誌伴隨着字符串拼接的效率問題,一行代碼打印System.out.print()
對系統來說輕而易舉,但十萬到百萬甚至千萬的字符替換就需要考慮效率更高的替換方式。
簡介
如果實際寫過企業級應用的人都知道,打印日誌都是爲了方便我們排查問題。從簡單的log
各種級別的output
,到海量日誌中通過requestId
或traceId
去跟蹤調用鏈路。
這些日誌的拼接方式,都要通過字符串截取、拼接、再組合來實現。
而Java
語言中,常用的日誌系統有log4j
、logback
、jul
等。其中爲了達到日誌系統實現與應用快速替換的方式,採用門面模式和橋接模式實現的slf4j
,都需要面對快速的字符串處理。
該篇文章主要簡述slf4j
與log4j2
結合在處理帶{}
字符串的替換過程。
打印
這裏是基於Maven
項目來演示,首先我們需要寫一串簡單的代碼,並將log4j.properties
文件寫入resource
中。
pom.xml
文件的dependencies
:
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.30</version>
</dependency>
簡單打印:
import lombok.extern.slf4j.Slf4j;
@Slf4j
public class Slf4jTest {
public static void main(String[] args) {
// 這裏使用 lombok 插件的 slf4j 註解
// log 源碼在 org.slf4j.Logger
// 實際調用爲 org.slf4j.impl.Log4jLoggerAdapter ,它實現了一個 wrapper,去包裝實現 log4j org.apache.log4j.Logger
log.info("qqq{}ppp", 123);
// 打印結果:
[INFO ] 2020-06-10 22:56:50,872 method:com.test.slf4j.Slf4jTest.main(Slf4jTest.java:9)qqq123ppp
}
}
log4j.properties
的配置
log4j.rootLogger=info,stdout # info 級別的日誌,stdout 標誌符的打印追加器(appender)生效
log4j.appender.stdout= org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target= System.out
log4j.appender.stdout.layout= org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern= [%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%m%n
我們如果debug
代碼的話,會發現在調用slf4j
代碼的時候,程序已經拼接好了字符串,它的調用鏈路是
org.slf4j.impl.Log4jLoggerAdapter#info(java.lang.String, java.lang.Object)
-> org.slf4j.helpers.MessageFormatter#format(java.lang.String, java.lang.Object)
-> org.slf4j.helpers.MessageFormatter#arrayFormat(java.lang.String, java.lang.Object[])
-> org.slf4j.helpers.MessageFormatter#arrayFormat(java.lang.String, java.lang.Object[], java.lang.Throwable)
在這裏最關鍵的代碼是MessageFormatter
,它實現了一套基於StringBuilder
和字符串動態索引的算法,代碼如下:
int i = 0;
int j;
// use string builder for better multicore performance
// StringBuilder 來提高多核性能,無鎖,非線程安全,並提前預支了 50 個字符位
StringBuilder sbuf = new StringBuilder(messagePattern.length() + 50);
int L;
// argArray 是輸入替換的 Object 數組,這裏是 new Object[]{ 123 }
for (L = 0; L < argArray.length; L++) {
// DELIM_STR == {} 字符
j = messagePattern.indexOf(DELIM_STR, i);
// 無 {}
if (j == -1) {
// no more variables
if (i == 0) { // this is a simple string
// 直接返回
return new FormattingTuple(messagePattern, argArray, throwable);
} else { // add the tail string which contains no variables and return
// the result.
// 還需要截斷下字符
sbuf.append(messagePattern, i, messagePattern.length());
return new FormattingTuple(sbuf.toString(), argArray, throwable);
}
} else {
// 不是轉義字符,類似這種:\{}
if (isEscapedDelimeter(messagePattern, j)) {
if (!isDoubleEscaped(messagePattern, j)) {
L--; // DELIM_START was escaped, thus should not be incremented
sbuf.append(messagePattern, i, j - 1);
sbuf.append(DELIM_START);
i = j + 1;
} else {
// The escape character preceding the delimiter start is
// itself escaped: "abc x:\\{}"
// we have to consume one backward slash
sbuf.append(messagePattern, i, j - 1);
deeplyAppendParameter(sbuf, argArray[L], new HashMap<Object[], Object>());
i = j + 2;
}
} else {
// normal case
sbuf.append(messagePattern, i, j);
// 其中附帶數組寫入,如 boolean[],char[]等,argArray[L] 傳入的即使是基本類型,也可以通過自動裝配,實現對象類型的轉換
deeplyAppendParameter(sbuf, argArray[L], new HashMap<Object[], Object>());
i = j + 2;
}
}
}
// append the characters following the last {} pair.
sbuf.append(messagePattern, i, messagePattern.length());
擴展
如果要在項目中對大量字符進行替換拆分,其實可以複用MessageFormatter
這個類。經過了無數次考驗,穩定性和效率那必定是很高的了。
所以基於MessageFormatter
重新複寫了一個簡版的MessageFormatter
只返回字符串:
public class MessageFormatter {
private static final char DELIM_START = '{';
private static final String DELIM_STR = "{}";
private static final char ESCAPE_CHAR = '\\';
public static String format(final String messagePattern, final Object... argArray) {
int i = 0;
int j;
// use string builder for better multicore performance
StringBuilder sbuf = new StringBuilder(messagePattern.length() + 50);
int L;
for (L = 0; L < argArray.length; L++) {
j = messagePattern.indexOf(DELIM_STR, i);
if (j == -1) {
// no more variables
if (i == 0) { // this is a simple string
return messagePattern;
} else { // add the tail string which contains no variables and return
// the result.
sbuf.append(messagePattern, i, messagePattern.length());
return sbuf.toString();
}
} else {
if (isEscapedDelimeter(messagePattern, j)) {
if (!isDoubleEscaped(messagePattern, j)) {
L--; // DELIM_START was escaped, thus should not be incremented
sbuf.append(messagePattern, i, j - 1);
sbuf.append(DELIM_START);
i = j + 1;
} else {
// The escape character preceding the delimiter start is
// itself escaped: "abc x:\\{}"
// we have to consume one backward slash
sbuf.append(messagePattern, i, j - 1);
deeplyAppendParameter(sbuf, argArray[L], new HashMap<>());
i = j + 2;
}
} else {
// normal case
sbuf.append(messagePattern, i, j);
deeplyAppendParameter(sbuf, argArray[L], new HashMap<>());
i = j + 2;
}
}
}
// append the characters following the last {} pair.
sbuf.append(messagePattern, i, messagePattern.length());
return sbuf.toString();
}
private static boolean isDoubleEscaped(String messagePattern, int delimeterStartIndex) {
return delimeterStartIndex >= 2 && messagePattern.charAt(delimeterStartIndex - 2) == ESCAPE_CHAR;
}
private static boolean isEscapedDelimeter(String messagePattern, int delimeterStartIndex) {
if (delimeterStartIndex == 0) {
return false;
}
char potentialEscape = messagePattern.charAt(delimeterStartIndex - 1);
return potentialEscape == ESCAPE_CHAR;
}
// special treatment of array values was suggested by 'lizongbo'
private static void deeplyAppendParameter(StringBuilder sbuf, Object o, Map<Object[], Object> seenMap) {
if (o == null) {
sbuf.append("null");
return;
}
if (!o.getClass().isArray()) {
safeObjectAppend(sbuf, o);
} else {
// check for primitive array types because they
// unfortunately cannot be cast to Object[]
if (o instanceof boolean[]) {
booleanArrayAppend(sbuf, (boolean[]) o);
} else if (o instanceof byte[]) {
byteArrayAppend(sbuf, (byte[]) o);
} else if (o instanceof char[]) {
charArrayAppend(sbuf, (char[]) o);
} else if (o instanceof short[]) {
shortArrayAppend(sbuf, (short[]) o);
} else if (o instanceof int[]) {
intArrayAppend(sbuf, (int[]) o);
} else if (o instanceof long[]) {
longArrayAppend(sbuf, (long[]) o);
} else if (o instanceof float[]) {
floatArrayAppend(sbuf, (float[]) o);
} else if (o instanceof double[]) {
doubleArrayAppend(sbuf, (double[]) o);
} else {
objectArrayAppend(sbuf, (Object[]) o, seenMap);
}
}
}
private static void safeObjectAppend(StringBuilder sbuf, Object o) {
try {
String oAsString = o.toString();
sbuf.append(oAsString);
} catch (Throwable t) {
Util.report("SLF4J: Failed toString() invocation on an object of type [" + o.getClass().getName() + "]", t);
sbuf.append("[FAILED toString()]");
}
}
private static void objectArrayAppend(StringBuilder sbuf, Object[] a, Map<Object[], Object> seenMap) {
sbuf.append('[');
if (!seenMap.containsKey(a)) {
seenMap.put(a, null);
final int len = a.length;
for (int i = 0; i < len; i++) {
deeplyAppendParameter(sbuf, a[i], seenMap);
if (i != len - 1)
sbuf.append(", ");
}
// allow repeats in siblings
seenMap.remove(a);
} else {
sbuf.append("...");
}
sbuf.append(']');
}
private static void booleanArrayAppend(StringBuilder sbuf, boolean[] a) {
sbuf.append('[');
final int len = a.length;
for (int i = 0; i < len; i++) {
sbuf.append(a[i]);
if (i != len - 1)
sbuf.append(", ");
}
sbuf.append(']');
}
private static void byteArrayAppend(StringBuilder sbuf, byte[] a) {
sbuf.append('[');
final int len = a.length;
for (int i = 0; i < len; i++) {
sbuf.append(a[i]);
if (i != len - 1)
sbuf.append(", ");
}
sbuf.append(']');
}
private static void charArrayAppend(StringBuilder sbuf, char[] a) {
sbuf.append('[');
final int len = a.length;
for (int i = 0; i < len; i++) {
sbuf.append(a[i]);
if (i != len - 1)
sbuf.append(", ");
}
sbuf.append(']');
}
private static void shortArrayAppend(StringBuilder sbuf, short[] a) {
sbuf.append('[');
final int len = a.length;
for (int i = 0; i < len; i++) {
sbuf.append(a[i]);
if (i != len - 1)
sbuf.append(", ");
}
sbuf.append(']');
}
private static void intArrayAppend(StringBuilder sbuf, int[] a) {
sbuf.append('[');
final int len = a.length;
for (int i = 0; i < len; i++) {
sbuf.append(a[i]);
if (i != len - 1)
sbuf.append(", ");
}
sbuf.append(']');
}
private static void longArrayAppend(StringBuilder sbuf, long[] a) {
sbuf.append('[');
final int len = a.length;
for (int i = 0; i < len; i++) {
sbuf.append(a[i]);
if (i != len - 1)
sbuf.append(", ");
}
sbuf.append(']');
}
private static void floatArrayAppend(StringBuilder sbuf, float[] a) {
sbuf.append('[');
final int len = a.length;
for (int i = 0; i < len; i++) {
sbuf.append(a[i]);
if (i != len - 1)
sbuf.append(", ");
}
sbuf.append(']');
}
private static void doubleArrayAppend(StringBuilder sbuf, double[] a) {
sbuf.append('[');
final int len = a.length;
for (int i = 0; i < len; i++) {
sbuf.append(a[i]);
if (i != len - 1)
sbuf.append(", ");
}
sbuf.append(']');
}
}
測試結果:
System.out.println(MessageFormatter.format("qqq{}ppp{}end", 123, 321));
打印結果:qqq123ppp321end