Building API objects
All data types in the Java API Client are immutable. Object creation uses thebuilder pattern that was popularized inEffective Java in 2008.
ElasticsearchClient esClient = createClient();CreateIndexResponse createResponse = esClient.indices().create( new CreateIndexRequest.Builder() .index("my-index") .aliases("foo", new Alias.Builder().isWriteIndex(true).build() ) .build());Note that a builder should not be reused after itsbuild() method has been called.
Although this works nicely, having to instantiate builder classes and call thebuild() method is a bit verbose. So every property setter in the Java API Client also accepts a lambda expression that takes a newly created builder as a parameter and returns a populated builder. The snippet above can also be written as:
ElasticsearchClient esClient = createClient();CreateIndexResponse createResponse = esClient.indices() .create(createIndexBuilder -> createIndexBuilder .index("my-index") .aliases("foo", aliasBuilder -> aliasBuilder .isWriteIndex(true) ) );This approach allows for much more concise code, and also avoids importing classes (and even remembering their names) since types are inferred from the method parameter signature.
Note in the above example that builder variables are only used to start a chain of property setters. The names of these variables are therefore unimportant and can be shortened to improve readability:
ElasticsearchClient esClient = createClient();CreateIndexResponse createResponse = esClient.indices() .create(c -> c .index("my-index") .aliases("foo", a -> a .isWriteIndex(true) ) );Builder lambdas become particularly useful with complex nested queries like the one below, taken from theintervals query API documentation.
This example also highlights a useful naming convention for builder parameters in deeply nested structures. For lambda expressions with a single argument, Kotlin provides the implicitit parameter and Scala allows use of_. This can be approximated in Java by using an underscore or a single letter prefix followed by a number representing the depth level (i.e._0,_1, orb0,b1 and so on). Not only does this remove the need to create throw-away variable names, but it also improves code readability. Correct indentation also allows the structure of the query to stand out.
ElasticsearchClient esClient = createClient();SearchResponse<SomeApplicationData> results = esClient .search(b0 -> b0 .query(b1 -> b1 .intervals(b2 -> b2 .field("my_text") .allOf(b3 -> b3 .ordered(true) .intervals(b4 -> b4 .match(b5 -> b5 .query("my favorite food") .maxGaps(0) .ordered(true) ) ) .intervals(b4 -> b4 .anyOf(b5 -> b5 .intervals(b6 -> b6 .match(b7 -> b7 .query("hot water") ) ) .intervals(b6 -> b6 .match(b7 -> b7 .query("cold porridge") ) ) ) ) ) ) ), SomeApplicationData.class);- Search results will be mapped to
SomeApplicationDatainstances to be readily available to the application.
The source code for the examples above can be found in theJava API Client tests.