Java Experience @JavaExpShare

Java developer who just wants to share some experience with community Russia, Moscow Joined August 2019

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Java Experience @JavaExpShare

6 years ago

Pageable object could specify sorting. Sort object have two properties: - Direction for ascending or descending sorting - Fields to make sorting on #Java #100DaysOfCode #spring

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The difference between Pageable responses: - Page returns page + pages count. To achieve this, additional query count will be executed. So we have small overhead - Slice returns page and knows whether next slice is available - List returns just current page #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

To effective work with Pageable we extends JpaRepository from #spring data JPA. Now we can just pass Pageable as method parameter inside repository and spring will do pagination and sorting for us. Pageable can return: - Page - Slice - List #100DaysOfCode #Java

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Java Experience @JavaExpShare

6 years ago

Now we can annotate parameter inside resource and #Jersey will construct and inject Pageable for us. Then we can simple pass it into spring data repository that supports pagination and that's all! #Java #100DaysOfCode #spring

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Java Experience @JavaExpShare

6 years ago

Finally we can construct our Pageable from @queryparam with help of ValueParamProvider and InjectionManager. I use @defaultvalue to provide default value for property if none specified. By default there is no sorting and display first page with 15 items. #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

To make #Jersey know about our custom provider we should register it inside main configuration file with help of AbstractBinder. Here we specify binding and scope. From now on all the injections inside custom provider will start to work. #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

Here the interesting part. We pass the injection manager into function implementation class, so we can inject our @queryparam. Then we can construct Pageable class from them. #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

Next we implement ValueParamProvider interface from #Jersey. It has 2 abstract methods: - getValueProvider() here we check for method parameter and return Function that construct that parameter -getPriority() is priority for provider execution #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

First of all we need to declare our custom annotation. Here we specify: - @Target is where we can use this annotation. On methods, on classes etc - @retention is retention policy. Indicates whether annotation should be stored inside class and available to JVM #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

To make such pagination and sorting for request we will specify 3 @queryparam. Then construct Pageable. It is ok, but not perfect Imagine we can write single method parameter as Pageable and Jersey will inject @queryparam inside. Let's find out how to do that #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

For pagination i will pass 2 parameters: - page is page number - size is page size For sorting: - sort is sorting field + order The query string will be like: /rest/vacancies?page=0&size=5&sort=id+desc where page, size and sort our @queryparam values. #Java #Jersey #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

Hello everyone! Hope all of you had good holidays and ready for learning :) Let's write something cool. As you might know good REST API should support pagination and sorting With #Jersey we can implement this with @queryparam and i will show how #100DaysOfCode #NewYear2020 #Java

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Java Experience @JavaExpShare

6 years ago

For @queryparam in #swagger we can specify array of parameters contains: - in: PathParam.QUERY - name - description - schema with type, example and default value #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

Well documented API is very important. In #Java we have javadoc to document our code. It is basically block of comments. Common things we can specify: - description what is going on - @param method parameters - @return what is returned #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

You can describe request body parameters with #swagger. No surprise annotation name is @RequestBody. Inside you can provide: - description - is body required or not - content with @schema with implementation or @ExampleObject with raw example. #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

To describe different parameters for resource, such as path parameters, query parameters, #swagger provides @parameter annotation: - in: where this parameter should be: header, query, cookie, path - name - description - required - examples #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

Inside @Operation in #swagger we can specify: - summary: basic description for endpoint - tags: to group up requests by tags - request body - responses: available server responses with codes and meanings - security: security requirements #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

Let's discuss basic annotations in #swagger. Once again, swagger allows us to describe our API, so others can easily use it. This technic also famous as OpenAPI. In REST application we have resources. To make it visible to swagger, annotate it with @Operation #Java #100DaysOfCode

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Java Experience @JavaExpShare

6 years ago

Inside DTO class you may have circular references. As example: Vacancy contains VacancyDetails, same time Details have reference to Vacancy. To deserialize such classes with #Jackson use: - @JsonManagedReference on parent ref - @JsonBackReference on child ref #100DaysOfCode #Java

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Java Experience @JavaExpShare

6 years ago

If we want to validate fields inside complex object, we should use @valid annotation. This launches cascade validation. If we have another complex object inside this object, annotate it with @valid as well to cascade further. #100DaysOfCode #Java