简介
本文将会介绍R2DBC的H2实现r2dbc-h2的应用办法和要留神的事项。一起来看看吧。
H2数据库简介
什么是H2数据库呢？
H2是一个Java SQL database，它是一个开源的数据库，运行起来十分快。
H2风行的起因是它既能够当做一个独立的服务器，也能够以一个嵌套的服务运行，并且反对纯内存模式运行。
H2的jar包十分小，只有2M大小，所以非常适合做嵌套式数据库。
如果作为嵌入式数据库，则须要将h2*.jar增加到classpath中。
上面是一个简略的建设H2连贯的代码：
import java.sql.*;public class Test { public static void main(String[] a) throws Exception { Connection conn = DriverManager. getConnection("jdbc:h2:~/test", "sa", ""); // add application code here conn.close(); }}如果给定地址的数据库并不存在，
同时H2还提供了一个简略的治理界面，应用上面的命令就能够启动H2治理界面：
java -jar h2*.jar默认状况下拜访http://localhost:8082就能够拜访到治理界面：
r2dbc-h2
r2dbc-h2是r2dbc spi的一种实现。同样的应用r2dbc-h2也提供了两种h2的模式，一种是文件系统，一种是内存。
同时还提供了事务反对，prepared statements和batch statements等个性的反对。
r2dbc-h2的Maven依赖
要想应用r2dbc-h2，咱们须要增加如下依赖：
<dependency> <groupId>io.r2dbc</groupId> <artifactId>r2dbc-h2</artifactId> <version>${version}</version></dependency>如果你体验snapshot版本，能够增加上面的依赖：
<dependency> <groupId>io.r2dbc</groupId> <artifactId>r2dbc-h2</artifactId> <version>${version}.BUILD-SNAPSHOT</version></dependency><repository> <id>spring-libs-snapshot</id> <name>Spring Snapshot Repository</name> <url>https://repo.spring.io/libs-snapshot</url></repository>建设连贯
h2有两种连贯形式，file和内存，咱们别离看一下都是怎么建设连贯的：
ConnectionFactory connectionFactory = ConnectionFactories.get("r2dbc:h2:mem:///testdb");Publisher<? extends Connection> connectionPublisher = connectionFactory.create();ConnectionFactory connectionFactory = ConnectionFactories.get("r2dbc:h2:file//my/relative/path");Publisher<? extends Connection> connectionPublisher = connectionFactory.create();咱们还能够通过ConnectionFactoryOptions来创立更加具体的连贯信息：
ConnectionFactoryOptions options = builder() .option(DRIVER, "h2") .option(PROTOCOL, "...") // file, mem .option(HOST, "…") .option(USER, "…") .option(PASSWORD, "…") .option(DATABASE, "…") .build();ConnectionFactory connectionFactory = ConnectionFactories.get(options);Publisher<? extends Connection> connectionPublisher = connectionFactory.create();// Alternative: Creating a Mono using Project ReactorMono<Connection> connectionMono = Mono.from(connectionFactory.create());下面的例子中，咱们应用到了driver,protocol, host,username,password和database这几个选项，除此之外H2ConnectionOption中定义了其余能够应用的Option：
public enum H2ConnectionOption { /** * FILE|SOCKET|NO */ FILE_LOCK, /** * TRUE|FALSE */ IFEXISTS, /** * Seconds to stay open or {@literal -1} to to keep in-memory DB open as long as the virtual machine is alive. */ DB_CLOSE_DELAY, /** * TRUE|FALSE */ DB_CLOSE_ON_EXIT, /** * DML or DDL commands on startup, use "\\;" to chain multiple commands */ INIT, /** * 0..3 (0=OFF, 1=ERROR, 2=INFO, 3=DEBUG) */ TRACE_LEVEL_FILE, /** * Megabytes (to override the 16mb default, e.g. 64) */ TRACE_MAX_FILE_SIZE, /** * 0..3 (0=OFF, 1=ERROR, 2=INFO, 3=DEBUG) */ TRACE_LEVEL_SYSTEM_OUT, LOG, /** * TRUE|FALSE */ IGNORE_UNKNOWN_SETTINGS, /** * r|rw|rws|rwd (r=read, rw=read/write) */ ACCESS_MODE_DATA, /** * DB2|Derby|HSQLDB|MSSQLServer|MySQL|Oracle|PostgreSQL|Ignite */ MODE, /** * TRUE|FALSE */ AUTO_SERVER, /** * A port number */ AUTO_SERVER_PORT, /** * Bytes (e.g. 512) */ PAGE_SIZE, /** * Number of threads (e.g. 4) */ MULTI_THREADED, /** * TQ|SOFT_LRU */ CACHE_TYPE, /** * TRUE|FALSE */ PASSWORD_HASH;}当然还有最间接的database选项：
r2dbc:h2:file//../relative/file/namer2dbc:h2:file///absolute/file/namer2dbc:h2:mem:///testdb咱们还能够通过H2特有的代码H2ConnectionFactory来创立：
H2ConnectionFactory connectionFactory = new H2ConnectionFactory(H2ConnectionConfiguration.builder() .inMemory("...") .option(H2ConnectionOption.DB_CLOSE_DELAY, "-1") .build());Mono<Connection> connection = connectionFactory.create();CloseableConnectionFactory connectionFactory = H2ConnectionFactory.inMemory("testdb");Mono<Connection> connection = connectionFactory.create();参数绑定
在应用prepare statement的时候，咱们须要进行参数绑定：
connection .createStatement("INSERT INTO person (id, first_name, last_name) VALUES ($1, $2, $3)") .bind("$1", 1) .bind("$2", "Walter") .bind("$3", "White") .execute()除了$符号绑定之外，还反对index绑定，如下所示：
Statement statement = connection.createStatement("SELECT title FROM books WHERE author = $1 and publisher = $2");statement.bind(0, "John Doe");statement.bind(1, "Happy Books LLC");批处理
咱们来看下r2dbc-h2是怎么来进行批处理的：
Batch batch = connection.createBatch();Publisher<? extends Result> publisher = batch.add("SELECT title, author FROM books") .add("INSERT INTO books VALUES('John Doe', 'HappyBooks LLC')") .execute();事务和Savepoint
r2dbc还反对事务和savepoint,咱们能够在事务中rollback到特定的savepoint。具体的代码如下：
Publisher<Void> begin = connection.beginTransaction();Publisher<Void> insert1 = connection.createStatement("INSERT INTO books VALUES ('John Doe')").execute();Publisher<Void> savepoint = connection.createSavepoint("savepoint");Publisher<Void> insert2 = connection.createStatement("INSERT INTO books VALUES ('Jane Doe')").execute();Publisher<Void> partialRollback = connection.rollbackTransactionToSavepoint("savepoint");Publisher<Void> commit = connection.commit();本文作者：flydean程序那些事本文链接：http://www.flydean.com/r2dbc-h2-in-depth/
本文起源：flydean的博客
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