SpringBoot：集成H2数据库并持久化，url中mem、file有什么区别？

H2依赖

<dependency>
    <groupId>com.h2databasegroupId>
    <artifactId>h2artifactId>
    <version>2.1.214version>
dependency>
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持久化配置

SpringBoot版本是2.3.12.RELEASE，下面有些配置看SpringBoot版本的，比如spring.datasource.schema是这个版本以下的，spring.sql.init.data是更高版本的

./dbfile 是把持久文件生成到程序启动路径下，你也可以自定义其他路径

# 数据源配置
spring.datasource.driver-class-name=org.h2.Driver
spring.datasource.schema=classpath:db/h2-schema.sql
spring.datasource.url=jdbc:h2:file:./dbfile
spring.datasource.username=root
spring.datasource.password=root
# 下面是控制台的配置
spring.h2.console.enabled=true
spring.h2.console.path=/h2-console
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H2 url的含义

先看以下两个常量，代表url开头与后半段，后半段的类型有mem内存模式、file本地文件模式、tcp|ssl远程模式，含义如下（参考http://www.h2database.com/html/features.html#embedded_databases）

org.h2.engine.Constants

	/**
     * The database URL prefix of this database.
     */
    public static final String START_URL = "jdbc:h2:";
    /**
     * The database URL format in simplified Backus-Naur form.
     */
    public static final String URL_FORMAT = START_URL +
            "{ {.|mem:}[name] | [file:]fileName | " +
            "{tcp|ssl}:[//]server[:port][,server2[:port]]/name }[;key=value...]";
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去驱动里查看，ConnectionInfo里把url截取，然后判断类型，当是file时，把持久化标识persistent标位了true，后续数据库启动和运行都会用到这个标识判断是否持久化

org.h2.engine.ConnectionInfo

	/**
     * Create a connection info object.
     *
     * @param u the database URL (must start with jdbc:h2:)
     * @param info the connection properties or {@code null}
     * @param user the user name or {@code null}
     * @param password
     *            the password as {@code String} or {@code char[]}, or
     *            {@code null}
     */
    public ConnectionInfo(String u, Properties info, String user, Object password) {
        u = remapURL(u);
        originalURL = url = u;
        if (!u.startsWith(Constants.START_URL)) {
            throw getFormatException();
        }
        if (info != null) {
            readProperties(info);
        }
        if (user != null) {
            prop.put("USER", user);
        }
        if (password != null) {
            prop.put("PASSWORD", password);
        }
        readSettingsFromURL();
        Object timeZoneName = prop.remove("TIME ZONE");
        if (timeZoneName != null) {
            timeZone = TimeZoneProvider.ofId(timeZoneName.toString());
        }
        setUserName(removeProperty("USER", ""));
        name = url.substring(Constants.START_URL.length());
        parseName();
        convertPasswords();
        String recoverTest = removeProperty("RECOVER_TEST", null);
        if (recoverTest != null) {
            FilePathRec.register();
            try {
                Utils.callStaticMethod("org.h2.store.RecoverTester.init", recoverTest);
            } catch (Exception e) {
                throw DbException.convert(e);
            }
            name = "rec:" + name;
        }
    }	

	private void parseName() {
        if (".".equals(name)) {
            name = "mem:";
        }
        if (name.startsWith("tcp:")) {
            remote = true;
            name = name.substring("tcp:".length());
        } else if (name.startsWith("ssl:")) {
            remote = true;
            ssl = true;
            name = name.substring("ssl:".length());
        } else if (name.startsWith("mem:")) {
            persistent = false;
            if ("mem:".equals(name)) {
                unnamed = true;
            }
        } else if (name.startsWith("file:")) {
            name = name.substring("file:".length());
            persistent = true;
        } else {
            persistent = true;
        }
        if (persistent && !remote) {
            name = IOUtils.nameSeparatorsToNative(name);
        }
    }
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