Add LambdaBodyLength

commit-id:01a58e06

builder/src/main/resources/application.yml

@@ -1552,3 +1552,10 @@ rules:
         enabled: true
         source: CHECKSTYLE
         uri: https://checkstyle.sourceforge.io/config_javadoc.html#JavadocMissingLeadingAsterisk
+    -
+        name: LambdaBodyLength
+        parent: TREEWALKER
+        level: COMPLEXITY
+        enabled: true
+        source: CHECKSTYLE
+        uri: https://checkstyle.sourceforge.io/config_sizes.html#LambdaBodyLength

builder/src/main/resources/rules/LambdaBodyLength.md

@@ -0,0 +1,48 @@
+
+Checks lambda body length.
+
+Rationale: Similar to anonymous inner classes, if lambda body becomes very long
+it is hard to understand and to see the flow of the method where the lambda is 
+defined. Therefore, long lambda body should usually be extracted to method. 
+
+Valid:
+````
+Runnable r3 = () -> { // ok, 10 lines
+    System.out.println(2); // line 2 of lambda
+    System.out.println(3);
+    System.out.println(4);
+    System.out.println(5);
+    System.out.println(6);
+    System.out.println(7);
+    System.out.println(8);
+    System.out.println(9);
+}; // line 10
+````
+
+Invalid:
+````
+Runnable r = () -> { // violation, 11 lines
+    System.out.println(2); // line 2 of lambda
+    System.out.println(3);
+    System.out.println(4);
+    System.out.println(5);
+    System.out.println(6);
+    System.out.println(7);
+    System.out.println(8);
+    System.out.println(9);
+    System.out.println(10);
+}; // line 11
+
+Runnable r2 = () -> // violation, 11 lines
+  "someString".concat("1") // line 1 of lambda
+              .concat("2")
+              .concat("3")
+              .concat("4")
+              .concat("5")
+              .concat("6")
+              .concat("7")
+              .concat("8")
+              .concat("9")
+              .concat("10")
+              .concat("11"); // line 11
+````