elastic search 学习

reference：https://www.elastic.co/docs

ElasticSearch Overview

ElasticSearch is a distributed, RESTful search and analytics engine built on Apache Lucene. It stores, searches, and analyzes large volumes of data quickly and in near real-time.

Principle

Indexing: Data is stored in indices, which are collections of documents. Each document is a JSON object.
Sharding & Replication: Indices are split into shards for scalability and replicated for fault tolerance.
Search: Uses inverted indices for fast full-text search.
RESTful API: All operations (CRUD, search, aggregation) are exposed via HTTP endpoints.

Usage

Install ElasticSearch
- Download from elastic.co
- Start with bin/elasticsearch
Basic Concepts
- Index: Like a database.
- Type: Deprecated, previously like a table.
- Document: A JSON object.
- Field: Key-value pairs in a document.

API Integration

ElasticSearch exposes a RESTful API. You can use curl, Postman, or any HTTP client.

1. Index a Document

bash 复制代码

curl -X POST "localhost:9200/my_index/_doc/1" -H 'Content-Type: application/json' -d'
{
  "title": "ElasticSearch Guide",
  "content": "ElasticSearch is a search engine."
}
'

2. Get a Document

bash 复制代码

curl -X GET "localhost:9200/my_index/_doc/1"

3. Search Documents

bash 复制代码

curl -X GET "localhost:9200/my_index/_search" -H 'Content-Type: application/json' -d'
{
  "query": {
    "match": {
      "content": "search engine"
    }
  }
}
'

4. Update a Document

bash 复制代码

curl -X POST "localhost:9200/my_index/_update/1" -H 'Content-Type: application/json' -d'
{
  "doc": {
    "title": "Updated Title"
  }
}
'

5. Delete a Document

bash 复制代码

curl -X DELETE "localhost:9200/my_index/_doc/1"

Java API Example

Add dependency in pom.xml:

xml 复制代码

<dependency>
  <groupId>org.elasticsearch.client</groupId>
  <artifactId>elasticsearch-rest-high-level-client</artifactId>
  <version>7.17.0</version>
</dependency>

Sample code:

java 复制代码

import org.elasticsearch.client.RestHighLevelClient;
import org.elasticsearch.client.RestClient;
import org.elasticsearch.action.index.IndexRequest;
import org.elasticsearch.action.index.IndexResponse;
import org.elasticsearch.common.xcontent.XContentType;

RestHighLevelClient client = new RestHighLevelClient(
    RestClient.builder(new HttpHost("localhost", 9200, "http"))
);

IndexRequest request = new IndexRequest("my_index").id("1")
    .source("{\"title\":\"ElasticSearch Guide\"}", XContentType.JSON);

IndexResponse response = client.index(request, RequestOptions.DEFAULT);
client.close();

Summary:

ElasticSearch is a scalable, distributed search engine. Use its RESTful API for CRUD and search operations. Integrate via HTTP or official clients (Java, Python, etc.).