包含了HyperSQL项目的源码，已经转化为Maven项目，可以用Eclipse或者IDEA直接导入。
类org.hssqldb.server.Server是启动的入口，运行这个类在控制台里会出现下面的输出:
[Server@28d93b30]: Startup sequence initiated from main() method
[Server@28d93b30]: Could not load properties from file
[Server@28d93b30]: Using cli/default properties only
[Server@28d93b30]: Initiating startup sequence...
[Server@28d93b30]: Server socket opened successfully in 6 ms.
[Server@28d93b30]: Database [index=0, id=0, db=file:test, alias=] opened successfully in 3233 ms.
[Server@28d93b30]: Startup sequence completed in 3241 ms.
[Server@28d93b30]: 2018-01-31 11:19:44.077 HSQLDB server 2.3.5 is online on port 9001
[Server@28d93b30]: To close normally, connect and execute SHUTDOWN SQL
[Server@28d93b30]: From command line, use [Ctrl]+[C] to abort abruptly输出信息中比较有用的是[Server@28d93b30]: 2018-01-31 11:19:44.077 HSQLDB server 2.3.5 is online on port 9001 这一行，这表明服务器现在监听9001端口，之后如果要用JDBC去连接，端口就是9001。
程序内部将启动一个后台线程serverThread，名字是“HSQLDB Server”
public int start() {
//ignore some codes..
serverThread = new ServerThread("HSQLDB Server ");
if (isDaemon) {
serverThread.setDaemon(true);
}
serverThread.start();
//ignore some codes..
return previousState;
}在serverThread启动的过程中会打开socket连接，用于处理外部的请求。对于每到来的一个请求，都会创建一个线程进行处理。
private void run() {
//ignore some codes...
try {
// Faster init first:
// It is huge waste to fully open the databases, only
// to find that the socket address is already in use
openServerSocket();
} catch (Exception e) {
setServerError(e);
printError("run()/openServerSocket(): ");
printStackTrace(e);
shutdown(true);
return;
}
//ignore some codes...
try {
/*
* This loop is necessary for UNIX w/ Sun Java 1.3 because
* in that case the socket.close() elsewhere will not
* interrupt this accept().
*/
while (socket != null) {
try {
handleConnection(socket.accept());
} catch (java.io.InterruptedIOException iioe) {}
}
} catch (IOException ioe) {
if (getState() == ServerConstants.SERVER_STATE_ONLINE) {
setServerError(ioe);
printError(this + ".run()/handleConnection(): ");
printStackTrace(ioe);
}
} catch (Throwable t) {
printWithThread(t.toString());
} finally {
shutdown(false); // or maybe getServerError() != null?
}
}
public void handleConnection(Socket s) {
Thread t;
Runnable r;
String ctn;
//ignore some codes...
if (serverProtocol == ServerConstants.SC_PROTOCOL_HSQL) {
r = new ServerConnection(s, this);
ctn = ((ServerConnection) r).getConnectionThreadName();
} else {
r = new WebServerConnection(s, (WebServer) this);
ctn = ((WebServerConnection) r).getConnectionThreadName();
}
t = new Thread(serverConnectionThreadGroup, r, ctn);
t.start();
printWithThread("handleConnection() exited");
}在ServerConnection类中，最终转到了odbcExecDirect函数里面的session.execute(r)方法对SQL语句进行处理。
private void odbcExecDirect(String inStatement) throws RecoverableOdbcFailure, IOException {
//ignore some codes...
Result r = Result.newExecuteDirectRequest();
r.setPrepareOrExecuteProperties(
statement, 0, 0, StatementTypes.RETURN_COUNT, 0,
ResultProperties.defaultPropsValue,
ResultConstants.RETURN_NO_GENERATED_KEYS, null, null);
Result rOut = session.execute(r);
//ignore some codes...
}在Session的execute方法里面EXECDIRECT和BATCHEXECDIRECT分别代表单条执行SQL语句和批量执行SQL语句所对应的逻辑。executeXXXStatement方法负责解析SQL语句并执行，performPostExecute方法负责将结果返回。
case ResultConstants.EXECDIRECT : {
Result result = executeDirectStatement(cmd);
result = performPostExecute(cmd, result);
return result;
}
case ResultConstants.BATCHEXECDIRECT : {
isBatch = true;
Result result = executeDirectBatchStatement(cmd);
result = performPostExecute(cmd, result);
return result;
}对于SQL解析部分，HyperSQL里面没有采用流行的开源工具antlr而是自己实现了解析，这里不做过多分析。
如果想通过JDBC连接HyperSQL，首先需要在pom文件中加入下面的依赖：
<!-- https://mvnrepository.com/artifact/org.hsqldb/hsqldb -->
<dependency>
<groupId>org.hsqldb</groupId>
<artifactId>hsqldb</artifactId>
<version>2.4.0</version>
</dependency>之后可以通过标准的SQL语句对HyperSQL进行操作。
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class HyperSQLTest {
public static void main(String[] args) throws SQLException {
Connection conn = null;
String sql;
String url = "jdbc:hsqldb:hsql://127.0.0.1:9001";
try {
Class.forName("org.hsqldb.jdbcDriver");
System.out.println("成功加载HyperSQL驱动程序");
conn = DriverManager.getConnection(url);
Statement stmt = conn.createStatement();
sql = "create table student(NO char(20),name varchar(20),primary key(NO))";
int result = stmt.executeUpdate(sql);// executeUpdate语句会返回一个受影响的行数，如果返回-1就没有成功
if (result != -1) {
System.out.println("创建数据表成功");
sql = "insert into student(NO,name) values('2012001','123')";
result = stmt.executeUpdate(sql);
sql = "insert into student(NO,name) values('2012002','123')";
result = stmt.executeUpdate(sql);
sql = "select * from student";
ResultSet rs = stmt.executeQuery(sql);// executeQuery会返回结果的集合，否则返回空值
System.out.println("学号\t姓名");
while (rs.next()) {
System.out.println(rs.getString(1) + "\t" + rs.getString(2));// 入如果返回的是int类型可以用getInt()
}
}
} catch (SQLException e) {
System.out.println("HyperSQL操作错误");
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
} finally {
conn.close();
}
}
}