Archive: April 2020

Java Joy: Using Functions To Replace Values In Strings

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Hubert Klein Ikkink

Since Java 9 we can use a function as argument for the Matcher.replaceAll method. The function is invoked with a single argument of type MatchResult and must return a String value. The MatchResult object contains a found match we can get using the group method. If there are capturing groups in the regular expression used for replacing a value we can use group method with the capturing group index as argument.

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Practical Protobuf - First call

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Peter Steman

In the previous blog I started my journey into Protobuf and introduced my first steps by introducing an example Contract service and some business operations on it.
Now let’s start with diving into details of how to model the gRPC calls.

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Java Joy: Using Named Capturing Groups In Regular Expressions

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Hubert Klein Ikkink

In Java we can define capturing groups in regular expression. We can refer to these groups (if found) by the index from the group as defined in the regular expression. Instead of relying on the index of the group we can give a capturing group a name and use that name to reference the group. The format of the group name is ?<name> as first element of the group definition. The name of the group can be used with the group method of the Matcher class. Also we can use the name when we want to reference the capturing group for example with the replaceAll method of a Matcher object. The format is ${name} to reference the group by name. Finally we can use a named capturing group also as backreference in a regular expression using the syntax \k<name>.

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Clojure Goodness: Checking Predicate For Every Or Any Element In A Collection

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Hubert Klein Ikkink

In Clojure we can use several functions to see if at least one or all elements in a collection return true or false for a predicate. The function every? only returns true if the predicate function returns true for all elements in the collection. To function not-every? return true if a predicate function return false for all elements in a collection. The some function is a bit different (notice there is no ?) and returns the first logical true value from the predicate function for the elements in the collection. So the return type of the predicate doesn’t have to be a Boolean value and then the return type of some is also not a Boolean. If the predicate returns a Boolean value we can use some like a `any` function (any is not part of Clojure). Clojure provides a not-any? function that returns true if the predicate function returns false for one element in the collection and false otherwise.

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Practical Protobuf - Introduction

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Peter Steman

As a fan of DDD I sometimes struggle to map the business needs into the current industry standard REST because of its technical nature and entity orientation.
So I went looking for an alternative and found a couple of possible candidates, gRPC+Protobuf, Thrift and Avro.
Of these, it looks like gRPC+Protobuf has the most traction at the moment. It also has a solid future ahead as it is a strategic choice within Google.
So let’s dive in and find out…​.

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Clojure Goodness: Splitting Strings

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Hubert Klein Ikkink

In Clojure we can use the clojure.string/split function to split a string, based on a regular expression, into a vector with string values. Optionally we can also specify a limit on the maximum number of returned string values we want. If we want to split a string based on the newline characters we can use the function clojure.string/split-lines that returns a vector where each element is a line from the original multi-line string.

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Clojure Goodness: Replacing Matching Values In String

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Hubert Klein Ikkink

We can search for a value in a string and replace it with another value using the clojure.string/replace function. The first parameter is the original string value that we want to replace parts of. The second parameter can be a string value or regular expression. The last parameter is the replacement value that can be a string value or a function that returns a string value. The function itself gets either a string argument if the match has no nested groups (when match is a regular expression) or a vector with a complete match followed by the nested groups when the match has nested groups.

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