add multi datasource support

mybatis-flex-core/src/main/java/com/mybatisflex/core/datasource/DataSourceKey.java

@@ -15,6 +15,8 @@
  */
 package com.mybatisflex.core.datasource;
 
+import java.util.function.Supplier;
+
 public class DataSourceKey {
 
     private static ThreadLocal<String> keyThreadLocal = new ThreadLocal<>();
@@ -23,6 +25,24 @@ public class DataSourceKey {
         keyThreadLocal.set(environmentId);
     }
 
+    public static <T> T use(String environmentId, Supplier<T> supplier) {
+        try {
+            use(environmentId);
+            return supplier.get();
+        } finally {
+            clear();
+        }
+    }
+
+    public static void use(String environmentId, Runnable runnable) {
+        try {
+            use(environmentId);
+            runnable.run();
+        } finally {
+            clear();
+        }
+    }
+
     public static void clear() {
         keyThreadLocal.remove();
     }

mybatis-flex-spring-boot-starter/src/main/java/com/mybatisflex/spring/boot/DataSourceBuilder.java

@@ -93,14 +93,13 @@ public class DataSourceBuilder {
 
 
     public static String attrToCamel(String string) {
-        String temp = string.toLowerCase();
+        int strLen = string.length();
-        int strLen = temp.length();
         StringBuilder sb = new StringBuilder(strLen);
         for (int i = 0; i < strLen; i++) {
-            char c = temp.charAt(i);
+            char c = string.charAt(i);
             if (c == '-') {
                 if (++i < strLen) {
-                    sb.append(Character.toUpperCase(temp.charAt(i)));
+                    sb.append(Character.toUpperCase(string.charAt(i)));
                 }
             } else {
                 sb.append(c);