提高微服务可用性的中间件CoralCache，针对这个问题，这篇文章详细介绍了相对应的分析和解答，希望可以帮助更多想解决这个问题的小伙伴找到更简单易行的方法。
当数据库出问题时能降级从本地缓存的数据中查询数据， CoralCache就是这样一个提高微服务可用性的中间件。
有些场景下，微服务依赖数据库中一些配置项或者数量很少的数据，但当数据库本身有问题时候，即使数据量很少，这个服务是不能正常工作；因此需要考虑一种能支持全量+极少变更的全局数据的场景，当数据库出问题时能降级从本地缓存的数据中查询数据，CoralCache就是这样一个提高微服务可用性的中间件。
CoralCache中间件架构如下图所示，通过@EnableLocal注解开启功能，应用启动后将配置的表数据一次性加载到内存中，内存中的数据逻辑结构和数据库中的逻辑结构一样。
图1. 架构图
内存查询引擎的原理是数据库查询降级发生后，Intercepter将拦截到的原始SQL传入查询引擎中，查询引擎解析SQL后得到表名、列名、where条件表达式，遍历InnerDB中对应表的数据行，并通过表达式计算引擎计算结果，计算结果为真则添加到结果集中最后返回给调用方。
计算引擎结构如下图所示，将where条件表达式转为后缀表达式后依次遍历后缀表达式，遇到操作数直接入栈，遇到操作符则根据操作符需要的操作数个数弹栈。
图2. 表达式计算引擎结构
然后根据操作符和弹出的操作数进行计算，不同操作符对应不同的计算方法，并将计算后的结果重新作为操作数入栈执到遍历完成，核心计算流程代码如下所示：
public Object calc(Expression where, InnerTable table, InnerRow row) {
try {
postTraversal(where);
} catch (Exception e) {
log.warn("calc error: {}", e.getMessage());
return false;
}
for (ExprObj obj : exprList) {
switch (obj.exprType()) {
case ITEM:
stack.push(obj);
break;
case BINARY_OP: {
ExprObj result = calcBinaryOperation(((ExprOperation) obj).getOperationType(), table, row);
stack.push(result);
break;
}
case UNARY_OP: {
ExprObj result = calcSingleOperation(((ExprOperation) obj).getOperationType(), table, row);
stack.push(result);
break;
}
case FUNCTION_OP: {
ExprObj result = calcFunctionOperation(((ExprOperation) obj).getOperationType(), table, row);
stack.push(result);
break;
}
default:
break;
}
}
return stack.pop();
}逻辑常见运算符为<、<=、>、>=、=等，它们的共性都是需要2个操作数并且返回值是布尔类型。
public ExprItem logicalCalculus(InnerTable table, InnerRow row, LogicalOperation logicalOperation) {
ExprObj second = stack.pop();
ExprObj first = stack.pop();
ExprItem result = new ExprItem();
result.setItemType(ItemType.T_CONST_OBJ);
Obj firstObj = getObj((ExprItem) first, table, row);
Obj secondObj = getObj((ExprItem) second, table, row);
boolean value = logicalOperation.apply(firstObj, secondObj);
result.setValue(new Obj(value, ObjType.BOOL));
return result;
}例子，以"="的实现来展示：
private ExprObj calcBinaryOperation(OperationType type, InnerTable table, InnerRow row) {
ExprObj result = null;
switch (type) {
case T_OP_EQ:
result = logicalCalculus(table, row, (a, b) -> ObjUtil.eq(a, b)); // 等于符号的实现
break;
...
default:
break;
}
return result;
}
public class ObjUtil {
private static ObjType resultType(ObjType first, ObjType second) {
return ObjType.RESULT_TYPE[first.ordinal()][second.ordinal()];
}
public static boolean eq(Obj first, Obj second) {
ObjType type = resultType(first.getType(), second.getType());
switch (type) {
case LONG: {
long firstValue = first.getValueAsLong();
long secondValue = second.getValueAsLong();
return firstValue == secondValue;
}
case DOUBLE: {
double firstValue = first.getValueAsDouble();
double secondValue = second.getValueAsDouble();
return Double.compare(firstValue, secondValue) == 0;
}
case TIMESTAMP: {
java.util.Date firstValue = first.getValueAsDate();
java.util.Date secondValue = first.getValueAsDate();
return firstValue.compareTo(secondValue) == 0;
}
...
default:
break;
}
throw new UnsupportedOperationException(first.getType() + " and " + second.getType() + " not support '=' operation.");
}
}数学运算和逻辑运算的流程都一样，只不过运算后的结果为数字类型。
除了上面说的逻辑运算和数学运算外，还支持进行模糊匹配的特殊操作符LIKE。
常见用法如下
LIKE "%HUAWEI" 匹配以HUAWEI结尾的字符串
LIKE "HUAWEI%" 匹配以HUAWEI开头的字符串
LIKE "A_B" 匹配以"A"起头且以"Z"为结尾的字串
LIKE "A?B" 同上
LIKE "%[0-9]%" 匹配含有数字的字符串
LIKE "%[a-z]%" 匹配含有小写字母字符串
LIKE "%[!0-9]%"匹配不含数字的字符串
?和_都表示单个字符
JAVA中实现LIKE的方案：将LIKE的模式转为JAVA中的正则表达式。
expr := wild-card + expr | wild-char + expr | escape + expr | string + expr | "" wild-card := % wild-char := _ escape := [%|_] string := [^%_]+ (One or > more characters that are not wild-card or wild-char)
public abstract class Token {
private final String value;
public Token(String value) {
this.value = value;
}
public abstract String convert();
public String getValue() {
return value;
}
}
public class ConstantToken extends Token {
public ConstantToken(String value) {
super(value);
}
@Override
public String convert() {
return getValue();
}
}
public class EscapeToken extends Token {
public EscapeToken(String value) {
super(value);
}
@Override
public String convert() {
return getValue();
}
}
public class StringToken extends Token {
public StringToken(String value) {
super(value);
}
@Override
public String convert() {
return Pattern.quote(getValue());
}
}
public class WildcardToken extends Token {
public WildcardToken(String value) {
super(value);
}
@Override
public String convert() {
return ".*";
}
}
public class WildcharToken extends Token {
public WildcharToken(String value) {
super(value);
}
@Override
public String convert() {
return ".";
}
}public class Tokenizer {
private Collection<Tuple> patterns = new LinkedList<>();
public <T extends Token> Tokenizer add(String regex, Function<String, Token> creator) {
this.patterns.add(new Tuple<Pattern, Function<String, Token>>(Pattern.compile(regex), creator));
return this;
}
public Collection<Token> tokenize(String clause) throws RuntimeException {
Collection<Token> tokens = new ArrayList<>();
String copy = String.copyValueOf(clause.toCharArray());
int position = 0;
while (!copy.equals("")) {
boolean found = false;
for (Tuple tuple : this.patterns) {
Pattern pattern = (Pattern) tuple.getFirst();
Matcher m = pattern.matcher(copy);
if (m.find()) {
found = true;
String token = m.group(1);
Function<String, Token> fn = (Function<String, Token>) tuple.getSecond();
tokens.add(fn.apply(token));
copy = m.replaceFirst("");
position += token.length();
break;
}
}
if (!found) {
throw new RuntimeException("Unexpected sequence found in input string, at " + position);
}
}
return tokens;
}
}public class LikeTranspiler {
private static Tokenizer TOKENIZER = new Tokenizer()
.add("^(\\[[^]]*])", ConstantToken::new)
.add("^(%)", WildcardToken::new)
.add("^(_)", WildcharToken::new)
.add("^([^\\[\\]%_]+)", StringToken::new);
public static String toRegEx(String pattern) throws ParseException {
StringBuilder sb = new StringBuilder().append("^");
for (Token token : TOKENIZER.tokenize(pattern)) {
sb.append(token.convert());
}
return sb.append("$").toString();
}
}直接调用LikeTranspiler的toRegEx方法将LIKE语法转为JAVA中的正则表达式。
private ExprObj calcBinaryOperation(OperationType type, InnerTable table, InnerRow row) {
ExprObj result = null;
switch (type) {
. . .
case T_OP_LIKE:
result = logicalCalculus(table, row, (a, b) -> ObjUtil.like(a, b));
break;
. . .
}
return result;
}
public static boolean like(Obj first, Obj second) {
Assert.state(first.getType() == ObjType.STRING, OperationType.T_OP_LIKE + " only support STRING.");
Assert.state(second.getType() == ObjType.STRING, OperationType.T_OP_LIKE + " only support STRING.");
String firstValue = (String) first.getRelValue();
String secondValue = (String) second.getRelValue();
String regEx = LikeTranspiler.toRegEx(secondValue);
return Pattern.compile(regEx).matcher(firstValue).matches();
}通过创建词法分析器并使用此方法进行转换，我们可以防止LIKE像这样的子句被转换为正则表达式%abc[%]%，该子句应将其中的任何子字符串与其中的子字符串匹配，该子句将与子字符串或匹配任何字符串。abc%.abc[.].abc.abc。
不同数据类型在进行计算时需要转型，具体的转化入下二维数组中。
// 不同类型计算后的类型
ObjType[][] RESULT_TYPE = {
//UNKNOWN BYTE SHORT INT LONG FLOAT DOUBLE DECIMAL BOOL DATE TIME TIMESTAMP STRING NULL
{ UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN },// UNKNOWN
{ UNKNOWN, LONG, LONG, LONG, LONG, DOUBLE, DOUBLE, DECIMAL, BOOL, UNKNOWN, UNKNOWN, UNKNOWN, LONG, UNKNOWN },// BYTE
{ UNKNOWN, LONG, LONG, LONG, LONG, DOUBLE, DOUBLE, DECIMAL, BOOL, UNKNOWN, UNKNOWN, UNKNOWN, LONG, UNKNOWN },// SHORT
{ UNKNOWN, LONG, LONG, LONG, LONG, DOUBLE, DOUBLE, DECIMAL, BOOL, UNKNOWN, UNKNOWN, UNKNOWN, LONG, UNKNOWN },// INT
{ UNKNOWN, LONG, LONG, LONG, LONG, DOUBLE, DOUBLE, DECIMAL, BOOL, UNKNOWN, UNKNOWN, UNKNOWN, LONG, UNKNOWN },// LONG
{ UNKNOWN, DOUBLE, DOUBLE, DOUBLE, DOUBLE, DOUBLE, DOUBLE, DECIMAL, BOOL, UNKNOWN, UNKNOWN, UNKNOWN, DOUBLE, UNKNOWN },// FLOAT
{ UNKNOWN, DOUBLE, DOUBLE, DOUBLE, DOUBLE, DOUBLE, DOUBLE, DECIMAL, BOOL, UNKNOWN, UNKNOWN, UNKNOWN, DOUBLE, UNKNOWN },// DOUBLE
{ UNKNOWN, DECIMAL, DECIMAL, DECIMAL, DECIMAL, DECIMAL, DECIMAL, DECIMAL, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, DECIMAL, UNKNOWN },// DECIMAL
{ UNKNOWN, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL, BOOL, UNKNOWN, UNKNOWN, UNKNOWN, BOOL, UNKNOWN },// BOOL
{ UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, TIMESTAMP, TIMESTAMP, TIMESTAMP, TIMESTAMP, UNKNOWN },// DATE
{ UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, TIMESTAMP, TIMESTAMP, TIMESTAMP, TIMESTAMP, UNKNOWN },// TIME
{ UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, TIMESTAMP, TIMESTAMP, TIMESTAMP, TIMESTAMP, UNKNOWN },// TIMESTAMP
{ UNKNOWN, LONG, LONG, LONG, LONG, DOUBLE, DOUBLE, DECIMAL, BOOL, TIMESTAMP, TIMESTAMP, TIMESTAMP, STRING, UNKNOWN },// STRING
{ UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN, UNKNOWN },// NULL
};点击关注，第一时间了解华为云新鲜技术~
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