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AceQL HTTP v6.0 - September 19, 2020

Server Installation and Configuration Guide




AceQL HTTP is a library of REST like APIs that allows you access to remote SQL databases over HTTP from any device that supports HTTP. This software has been designed to handle heavy traffic in production environments.

AceQL Draw

For example, a select command would be called from the client side using this http call with cURL:

$ curl --data-urlencode \
 "sql=select id, title, lname from customer where customer_id = 1" \

AceQL HTTP is authorized through an Open Source license: AceQL Open Source License (LGPL v2.1).

The AceQL HTTP framework consists of:

  • The AceQL Web Server.

  • Configuration Java classes injected at runtime. These are server classes that ensure both security and configuration. Many built-in classes are provided and standard configuration may be done without any coding.

  • The AceQL Client SDKs for C# , Java and Python that allow you to wrap AceQL HTTP API calls using fluent code:

    • // C# AceQL Client Calls Sample 
      string sql = "select id, title, lname from customer where customer_id = 1";
      using (AceQLCommand command = new AceQLCommand(sql, connection))
      using (AceQLDataReader dataReader = await command.ExecuteReaderAsync())
          while (dataReader.Read())
              int i = 0;
              Console.WriteLine("customer id   : " + dataReader.GetValue(i++));
              Console.WriteLine("customer title: " + dataReader.GetValue(i++));
              Console.WriteLine("customer name : " + dataReader.GetValue(i++));
    • // Java AceQL Client Calls Sample 
      String sql = "select id, title, lname from customer where customer_id = 1";
      try (Statement statement = connection.createStatement();
          ResultSet rs = statement.executeQuery(sql);) {
          while ( {
          int i = 1;
          System.out.println("customer id   : " + rs.getInt(i++));
          System.out.println("customer title: " + rs.getString(i++));
          System.out.println("customer name : " + rs.getString(i++));
    • # Python AceQL Client Calls Sample 
      with closing(connection.cursor()) as cursor:
          sql = "select id, title, lname from customer where customer_id = 1";
          rows = cursor.fetchall()
          for row in rows:
              print("customer id   : " + str(row[0]))
              print("customer title: " + row[1])
              print("customer name : " + row[2])

The execution of each AceQL HTTP API statement is conditioned by optional rules, defined in properties files and built-in or programmed configuration classes.

The AceQL Web Server embeds its own Tomcat 8.5 servlet container in order to run AceQL without any Java EE servlet container.

Note that AceQL can run inside any Java EE servlet container (see Running AceQL HTTP in a Java EE servlet container).

No Tomcat 8.5 expertise is required in order to configure and use the AceQL Web Server:

  • All Tomcat configuration values are optional: AceQL uses Tomcat 8.5 default values if no user configuration is done.
  • You may only be required to read short portions of the Tomcat 8.5 user documentation for using SSL & Certificates.

The AceQL Web Server consists of one Java jar. It is started by calling a Java class on the command line. All configuration elements are defined in a Java .properties file, named file in this document.

All communication between the client and the server uses HTTP/ HTTPS protocols. .

This User Guide covers:

  • Quickstart: this part describes how to run through complete setup using only configuration files and CSV files. (No programming and compiling are necessary.)

  • Advanced Usage: this part describes advanced setup and fine tuning. It includes powerful configuration and customization using injection code of your own or third party Java classes.

Technical operating environment

The AceQL HTTP server side is entirely written in Java, and functions identically under Microsoft Windows, Linux, and all versions of UNIX that support Java 8+ ,Servlet 3.1+ and JDBC 4.0+.

The only required third party installation is a Java 8+.

The following environments are supported in this version:

Actian Ingres 10+
IBM DB2 9.7+
IBM Informix 11.70+.
MariaDB 10.0+
Microsoft SQL Server 2008 R2+
MS Access 2010+
Oracle Database 11g Release 2+
Oracle MySQL 5.5+
PostgreSQL 8.4.1+
Sybase ASE 15.7+
Sybase SQL Anywhere 12+
Teradata Database 13+


  • All these databases have been intensively tested with AceQL.
  • The table designates the tested version. Prior versions should work correctly with their corresponding JDBC 4.0 driver.
  • AceQL will support all subsequent versions of each database.

Download and Installation

Linux / Unix Installation

Open a terminal and download with Wget.

$ wget

If you get a certificate error message, do one of the following:

  1. If the problem is that a known root CA is missing and when you are using Ubuntu or Debian, then you can solve the problem with this one line: sudo apt-getinstall ca-certificates. Then retry the Wget call.
  2. Retry the Wget call with --no-check-certificate at end of command line. Then check the PGP signature of the downloaded file using the corresponding .asc signature file available on download page using the PGP hyperlink.

Make the file executable and then run it:


This will create the aceql-http-6.0 folder that you can move where you want.

The full path to the final aceql-http-6.0 installation folder will be surnamed ACEQL_HOME in following text.

Example: if you run from /home/mike, then software is installed in /home/mike/aceql-http-6.0 which is the value of ACEQL_HOME.

Update the PATH (Optional)

Open a shell session and make sure java binary is in the PATH by typing

java -version on the command line.

Add java to your PATH if the command does not display Java version.

Add to your PATH the path to the bin directory of aceql-http-6.0 installation:

$ PATH=$PATH:/path/to/aceql-http-6.0/bin/
export PATH

Testing server installation

Open a shell session and make sure java binary is in the PATH by typing

java -version on the command line.

Add java to your PATH if the command does not display Java version.

Call the aceql-server script to display the AceQL version:

 $ aceql-server -version

It will display a line with all version info, like:

AceQL HTTP Community v6.0 - 19-Sep-2020

Windows Installation

Download AceQL Windows Installer.

Because the software installs and runs a Windows Service, you must be logged as a Windows Administrator to install AceQL.

Run the installer.

It will run AceQL at end of installation and display the Window:

AceQ HTTP GUI Main Windows

N.B: Because of a bug in all Java versions > 8 on Windows, the interface will appear "ugly" or "blurred" on Java version > 8 if you have increased Windows Screen Resolution Options to 125% or 150%. See Java Bug Database for more info. Set back Windows Screen Resolution to 100% for clean display.


The AceQL Manager servlet

All HTTP commands sent by the client side are received by the AceQL Manager servlet. The AceQL Manager servlet then:

  • Authenticates the client call
  • Extracts a JDBC Connection from the connection pool
  • Analyzes the JDBC statement that was received
  • Executes the statement if the JDBC statement matches the rules defined by the SQL Firewall Managers (see below)
  • Sends the result of the statement back to the client side

The file

Most AceQL configuration is carried out by defining properties in the aceql-server.propertie file, except the hostname and port, which are passed as start parameters.

The file is organized in Sections. Only the first Section must be configured in order to start the AceQL Manager. The Sections 2 to 4 allow to secure Aceql and are optional . (The subsequent Sections are covered later in Advanced Usage):

  1. Tomcat JDBC Connection Pool Section.
  2. User Authentication Section.
  3. SQL Firewall Managers Section.
  4. SSL Configuration Section.

Tomcat JDBC Connection Pool Section

This section allows you to define:

  1. The names of the databases to use.
  2. The JDBC parameters used to build the embedded The Tomcat 8.5 JDBC Connection Pool for each database.

The databases are defined with the databases property. If there are more than one database, separate each name with a comma:

# Database names separated by commas
databases = my_database1, my_database2 

Only the following four properties must be defined per database name if you want to use the Tomcat JDBC Connection Pool:

Property Value
driverClassName The fully qualified Java class name of the JDBC driver to be used.
url The connection URL to be passed to our JDBC driver to establish a connection.
username The connection username to be passed to our JDBC driver to establish a connection.
password The connection password to be passed to our JDBC driver to establish a connection.

Each property must be prefixed with the associated database name defined in databases property and a dot.

Example :

# Database names separated by commas
databases = my_database1, my_database2 

# Mandatory JDBC properties:
my_database1.driverClassName = org.postgresql.Driver
my_database1.url= jdbc:postgresql://localhost:5432/sampledb 
my_database1.username= user1  
my_database1.password= password1 

my_database2.driverClassName = oracle.jdbc.driver.OracleDriver
my_database2.url= jdbc:oracle:thin:my_database2@//localhost:1521/XE 
my_database2.username= user2 
my_database2.password= password2

You may add other properties supported by Tomcat JDBC Connection Pool, as defined in Common Attributes and in Enhanced Attributes.

Note: It is not mandatory to use Tomcat JDBC Connection Pool. If you want to use another preferred Connection Pool system, just comment the driverClassName property. Implementing another Connection Pool system is described in Advanced Connection Pool Management.

User Authentication Section

This section allows to define how to authenticate a remote use client that connects to the AceQL Server.

Authentication is defined through the injection of an "User Authenticator", a Java class that is injected at AceQL Server startup. It is a built-in or user-developed Java class that implements the UserAuthenticator interface built in AceQL.

The login method of the class is called when a remote client first connects to the AceQL and pass it's credentials (username and password). If the login method returns true, user access is granted, otherwise the user access is denied.

AceQL provides four built-in (and ready to use without any coding) User Authenticators:

User Authenticator Name Role Parameters
LdapUserAuthenticator Authenticates the remote client (username, password) against a LDAP server. URL of the LDAP server
SshUserAuthenticator Authenticates the remote client (username, password) against a SSH server. IP or host & port of the SSH server
WebServiceUserAuthenticator Authenticates the remote client (username, password) against a Web service. (See below). URL of the Web service & connection timeout.
WindowsUserAuthenticator Authenticates the remote client (username, password) against the Windows server on which the AceQL server is running. The Windows domain (optional).

Just select in the section the userAuthenticatorClassName to use, and fill the required parameters.

All the rest will be done automatically once the AceQL server is started.

The WebServiceUserAuthenticator usage

AceQL allows to authenticate remote client users against a Web service that is developed and deployed on you web infrastructure by your organization. This allows you to develop or use an existing a specific authentication program that is decoupled from AceQL. You can thus use whatever technology stack to authenticate remote client users, and wrap it in a Web service that is called by AceQL when a remote client user wants to authenticate.

The Web service must just implement these features:

  • It must accept the 2 POST parameters username and password.

  • It must return either:

    • The JSON string {"status"="OK"} if the authentication succeeds.
    • The JSON string {"status"="FAIL"} if the authentication fails.

SQL Firewall Managers Section

The SQL Firewall Managers Section allows to define SQL firewall rulesets to use for each database.

The rulesets are defines through one or more "SQL Firewall Managers", Java classes that are injected at AceQL Server startup. A SQL Firewall Manager It a built-in or user-developed Java class that implements the SqlFirewallManager interface.

A SqlFirewallManagerconcrete implementation allows to:

  • Define if a client user has the right to call a Statement.executeUpdate (i.e. call a statement that updates the database).
  • Define if a client user has the right to call a raw JDBC Statement that is not a PreparedStatement.
  • Define if a client user has the right to call the AceQL Metadata API.
  • Define a specific piece of Java code to analyze the source code of the SQL statement before allowing or not it's execution.

Multiple SqlFirewallManager may be defined and chained.

AceQL provides several built-in (and ready to use without any coding) SQL Firewall Managers:

SQL Firewall Manager Name Details
CsvRulesManager Manager that applies rules written in a CSV file. (See below).
DenyDclManager Manager that denies any DCL (Data Control Language) call.
DenyDdlManager Manager that denies any DDL (Data Definition Language) call.
DenyExecuteUpdateManager Manager that denies any update of the database. (The database will be accessed in read only mode).
DenyMetadataQueryManager Manager that denies the use of the AceQL Metadata Query API.
DenyStatementClassManager Manager that denies any call of he raw Statement Java class. (Calling Statements without parameters is forbidden).

Only the following property must be defined per database name if you want to add SQL Firewall Managers:


SqlFirewallManager may be chained in property value by separating class names by a comma.
When SqlFirewallManager classes are chained, an AND condition is applied to all the SqlFirewallManager execution conditions in order to compute final allow. For example, the allowExecuteUpdate() of each chained SqlFirewallManager instance must return true in order to allow updates of the database.

The following example defines two built in firewalls to chain for the sampledb database:

  • First DenyDdlManager will deny to pass DDL statements such as DROP, CREATE TABLE, etc.
  • SecondDenyExecuteUpdateManager will deny write access to database,

After AceQL server restart, remote clients won't be allowed to execute DDL statements nor to update the database.

The CsvRulesManager SQL Firewall Manager

The CsvRulesManager manager allows to define detailed rules just using a CSV file.

It checks each SQL request against the content of a CSV File. The CSV file is loaded in memory at AceQL server startup.

The name of the CSV file that will be used by a database is: <database>_rules_manager.csv, where <database> is the name of the database declared in the files. The file must be located in the same directory as the file used when starting the AceQL server.

The CSV file contains the rules for accessing the tables, with semicolon for separator:

  • First line contains the element names:

    username;table;delete;insert;select;update;optional comments

  • Subsequent lines contain the rules, with the values for each element:

    • username: AceQL username of the connected client.
    • table: the table name to access. Name must not include dots and prefixes.
    • delete: true if the username has the right to delete rows of the table, else false.
    • insert: true if the username has the right to insert rows in the table, else false.
    • select: true if the username has the right to select rows of the table, else false.
    • update: true if the username has the right to update rows of the table, else false.
    • Optional comments for the rule.

Note that:

  • public value may be used for the username column and means any username. At execution time: if a rule with public returns true for a CSV column, the rule supersedes other declared rules declared for specific users for the same CSV column.
  • all value is allowed for table column and means any table. At execution time: If a rule with all returns true for a CSV column, the rule supersedes other specific rules declared for specific tables for the same CSV column.

Here is an example of a documented CSV File: sampledb_rules_manager.csv.

SSL Configuration Section

This section is optional. It allows you to configure the Tomcat HTTP Connector in order to use SSL when calling AceQL Manager Servlet from the client side.

It also allows you to define the SSL Certificate to be used.

Set the SSLEnabled property to true, in order to say that the HTTP Connector will accept SSL calls from client side.

Each property must be prefixed by sslConnector.

Note: If SSLEnabled is set to true, AceQL HTTP Web server will accept only SSL connections, i.e. a non SSL call from client side with http scheme will fail.

To define SSL HTTP Connector attribute values, refer to the Tomcat 8.5 SSL Support documentation.

The following properties are mandatory and must be defined:

Mandatory Property Name Property Role
sslConnector.scheme Scheme to use. Must be set to "https"
sslConnector.keystoreFile The file containing the SSL/TLS certificates
sslConnector.keystorePass The keystore password
sslConnector.keyPass The certificate password

To create an SSL Certificate, refer to:

Sample file

Here is a documented example of an file:

Starting/Stopping the AceQL Web Server from Linux/Unix

Add your JDBC driver to the AceQL installation

Before starting the AceQL Web Server, drop you JDBC driver jar into

ACEQL_HOME/lib-jdbc directory or add it to the Java CLASSPATH.

Starting the AceQL Web Server

Open a shell and type:

$ aceql-server -start -host <hostname> -port <port number> -properties <file>


  • -host <hostname> hostname of the Web server

  • -port <port number> port number of the Web server. Defaults to 9090

  • -properties <file> properties file to use for this SQL Web server Session. Defaults to ACEQL_HOME/conf/

The console will display the properties used and will end with this line if everything is OK (assuming you choose 9090 for port.)

[ACEQL HTTP START] AceQL HTTP Web Server OK. Running on port 9090

If configuration errors occur, they are displayed with the tag



Starting the AceQL Web Server on port 9090

$ aceql-server -start -host localhost

The URL to use on the client side will be: http://localhost:9090/aceql

assuming the AceQL Manager Servlet Section contains the following line:


Starting the AceQL Web Server on port 9091

$ aceql-server -start -host -port 9091

The URL to use on the client side will be:

assuming the AceQL Manager Servlet Section contains the following line:


Using SSL from the client side

Assuming you have enabled SSL and defined a Certificate in the file, the URL to use on the client side will be:

Stopping the AceQL Web Server

To stop a running instance of the AceQL Web Server:

$ aceql-server-stop -port <port number>


-port <port number> port number of the Web server. Defaults to 9090

Linux: running the AceQL Web server as a service

The aceqlhttp wrapper allows to run AceQL program as a Linux service.

  • Click here to download
  • Copy to /etc/init.d/aceqlhttp (requires root privilege).
  • sudo chmod +x /etc/init.d/aceqlhttp
  • Then edit /etc/init.d/aceqlhttp and:
    • Modify JAVA_HOME to the path of you Java installation.
    • Modify ACEQL_HOME to the path of your AceQL installation.
    • Modify ACEQL_HOST and ACEQL_PORT with your hostname and port.
    • Modify CLASSPATH if you plan to inject your own Java classes (See Advanced Usage).


  • Test that it runs: sudo service aceqlhttp start
  • Test that it stop: sudo service aceqlhttp stop
  • Test that it restarts: sudo service aceqlhttp restart

Then check the content of the log file defined by LOG_PATH_NAME and which defaults to: /var/log/aceqlhttp.out.

Starting/Stopping the AceQL WebServer from Windows

Server maybe started within the current JVM, or as a Windows Service.

If you wish to run the AceQL HTTP Server as a Windows Service, it is highly recommended to test your configuration by starting once the server in Standard Mode.

The running options are fully described in the user interface help.

Advanced Usage

Development Environment

Setting up a development environment will allow you to develop your own Java classes that will be injected at runtime.

Create a Server project and add the jars of the:

  • <installation-directory>\AceQL\lib-server subdirectory & <installation-directory>\AceQL\lib-jdbc to your development CLASSPATH .

Or for Maven users:


AceQL Servlet Name Configuration

The AceQL Manager servlet Section in the aceql-server.proprties file allows you to define the name of the AceQL SQL Manager Servlet to call from the client side. The default name is aceql. It is the name that will be used in the URL by client calls:


Advanced Connection Pool Management

You may define your own preferred connection pool implementation, instead of using the default Tomcat JDBC Connection Pool.

This is done through your own implementation of the DatabaseConfigurator interface: overload the DatabaseConfigurator.getConnection() method in your concrete class implementation.

Your concrete implementations is passed to the AceQL as properties of the Database Configurators Section in the file, as described in the section:

  • The databaseConfiguratorClassName property lets you define your concrete implementation of DatabaseConfigurator.
  • You DatabaseConfigurator classes must be added to the CLASSPATH before the start of the AceQL Server.

Instances are loaded using a non-args constructor.

Advanced Authentication Configuration

In order to give access to remote client users to the AceQL server, you may develop entirely your own authentication mechanism. This is done through your own implementation of the UserAuthenticator interface: overload the login method UserAuthenticator.login() in your concrete class implementation.

Your concrete implementations is passed to the AceQL as properties of the User Authentication Section in the file, as described in the section

  • The userAuthenticatorClassName property lets you define your concrete implementation of UserAuthentication.
  • You UserAuthenticationclasses must be added to the CLASSPATH before the start of the AceQL Server.

Instances are loaded using a non-args constructor.

Tomcat HTTP Connector Configuration

Tomcat HTTP Connectors allow fine tuning of Tomcat 8.5.

It is possible to define properties for a unique HTTP Connector that will either accept HTTP or secured HTTPS calls. The properties must be defined in the HTTP Connector Attributes Section.

This section is optional. If no value is defined, default Tomcat values will be used for the default HTTP Connector.

You may define all attributes defined in the Tomcat HTTP Connector documentation, except SSL attributes that must be defined in the SSL Configuration Section.

Each property must be prefixed by connector.

# Example: Change default maxThreads from 200 to 300

ThreadPoolExecutor Configuration

The AceQL Manager serlvet is executed in asynchronous mode.

The ThreadPoolExecutor Section allows to define the parameters of the java.util.concurrent.ThreadPoolExecutor instance used to execute all servlet requests in async mode.

The properties to set in the file are:

Property Role Default Value
corePoolSize The number of threads to keep in the pool, even if they are idle. 100
maximumPoolSize The maximum number of threads to allow in the pool. 200
unit The time unit for the keepAliveTime argument. SECONDS
keepAliveTime When the number of threads is greater than the core, this is the maximum time that excess idle threads will wait for new tasks before terminating. 10
workQueueClassName The BlockingQueue class to use in ThreadPoolExecutor constructor. ArrayBlockingQueue
capacity The initial capacity of the BloquingQueue<Runnable>
(0 for no or default initial capacity.)

The properties are passed to the first ThreadPoolExecutor constructor.

See ThreadPoolExecutor class Javadoc for more info

Default values should be appropriate for most AceQL configurations.

Session Management

SessionConfigurator interface

After server authentication succeeds (through the UserAuthenticator.login() method), the AceQL Manager builds an authentication session id that is sent back to the client and will be used by each succeeding client call in order to authenticate the calls.

Session security is managed by implementing the SessionConfigurator interface that defines how to generate and verify the session id for (username, database) sessions.

Interface implementation allows you to:

  • Define how to generate a session id after client /login call
  • Define the session’s lifetime
  • Define how to verify that the stored session is valid and not expired

Session management default implementation

The default mechanism that builds an authentication session id is coded in the class


  • Session ids are generated using a SecureRandom with the SessionIdentifierGenerator class.
  • Session info (username, database) and session date/time creation are stored in a HashMap, whose key is the session id.
  • Session id is sent by client side at each API call. AceQL verifies that the HashMap contains the username and that the session is not expired to grant access to the API execution.

Benefits of this implementation are:

  • Session ids are short and generate less HTTP traffic.
  • Because session ids are short, they are easy to use “manuallyâ€� (with cURL, etc.)

The disadvantage is that session information is stored on the server side.

Session management using JWT

Session management using JWT is coded in JwtSessionConfigurator.

Session management is done using self-contained JWT (JSON Web Token).

See for more information on JWT.

A benefit of JWT is that no session information is stored on the server and that it allows full stateless mode.

A disadvantage of JWT is that the tokens are much longer and thus generate more http traffic and are less convenient to use "manually" (with cURL, etc.).

Activating JwtSessionConfigurator

Edit the file and uncomment the two lines:


Change the jwtSessionConfiguratorSecret property change it value with your own secret value.

Restart the AceQL Web Server for activation.

Creating your own session management

If you want to create your session management using your own session id generation and security rules, you can implement the SessionConfigurator in your own class, and then:

Add your class in the CLASSPATH.

Add you class name in the SessionConfigurator section in your file:


Restart the AceQL Web Server for activation.

Advanced Firewall Configuration

AceQL provides several built-in and ready to use SQL Firewall Managers, as described earlier in the SQL Firewall Managers Section chapter. You also may plug-in your own implementation or third party SQL firewalling tools.

The SqlFirewallManager interface allows you to code your own firewall rulesets or plug a third party software.

After coding you own SqlFirewallManager implementation, just declare the full class name in the sqlFirewallManagerClassNames property. Remember that SQL Firewall Managers may be chained: you may declare several classes.

The following example defines two firewalls to chain for the sampledb database:


Interacting with the JDBC Pool at runtime

The Servlets Section in allow to define you own servlets in order to interact with AceQL Web Server with different actions :

  • query info about JDBC pools in use,
  • modify a pool size,
  • etc.

The API DataSourceStore class allows to retrieve for each database the Tomcat org.apache.tomcat.jdbc.pool.DataSource corresponding to the Tomcat JDBC Pool created at AceQL Web server startup.

Running the AceQL Web Server

Running the AceQL Web Server without Windows Desktop

If you don’t have access to the Windows Desktop interface (running in a cloud instance, etc.) you can still run the AceQL HTTP Web Server from the command line.

  • see <installation-directory>\AceQL\bin\aceql-server.bat script.

You can also start/top the AceQL Web Server from you java programs, as explained in next section.

Starting/Stopping the AceQL WebServer from a Java program

You may start or stop the AceQL Server from a Java program calling the WebServerApi API.

Running AceQL HTTP in a Java EE servlet container

AceQL server side may be run inside a Java EE servlet container such as Tomcat.

This option may be preferred by users who already have a Java EE servlet container configured with all Connectors & SSL options, etc., and do want to recode the options in the file.


Install the files of installation directory webapp/WEB-INF/lib in the lib directory of your webapp.

If your JavaEE servlet container is not Tomcat >=7, it may not contain the Tomcat JDBC Pool: add webapp/WEB-INF/lib-tomcat/tomcat-jdbc-8.5.xx.jar jar in the /lib directory of your webapp.

If you have coded your own Configurators, deploy the classes in the /classes directory of your webapp.

AceQL servlet configuration in web.xml

Create and configure the file like normal, as described in The file. Do not configure the Tomcat Connector sections that will not be used.

In web.xml, define the AceQL Manager servlet that is defined in the file. This dual definition is required. The servlet class is. org.kawanfw.sql.servlet.ServerSqlManager.


Assuming the file is stored in c:\Users\Mike and you have defined the following aceQLManagerServletCallName in


then your web.xml should contain the following code:


<!—- Allows you to see immediately in servet container if servlet is OK or KO --> 
<load-on-startup>1</load-on-startup >

    <!-- Note the trailing /* in url-pattern --> 

Note the trailing /* in the URL pattern: this is required by the AceQL Manager that uses both the servlet name and elements in servlet path values to execute actions requested by the client side.

Testing the servlet configuration

After restarting your server, check you web server logs.

AceQL start statuses are written on standard output stream.

Type the HTTP address of each of your AceQL Manager servlets into a browser.

Example corresponding to previous web.xml:

It will display a JSON string and should display a status of "OK" and the current AceQL version:

    "status": "OK",
    "version": "AceQL HTTP v6.0 - 19-Sep-2020"

If not, the configuration errors are detailed for correction.

AceQL internals

State management / Stateful Mode

AceQL runs in "Stateful Mode": when creating a session on the client side with /login API, the AceQL servlet that is contacted extracts a JDBC Connection from the connection pool (with DatabaseConfigurator.getConnection()) and stores it in memory in a static Java Map.

The server's JDBC Connection is persistent, attributed to the client user, and will not be used by other users: the same Connection will be used for each JDBC call until the end of the session. This allows you SQL transactions to be created.

The Connection will be released from the AceQL Manager Servlet memory and released into the connection pool by a client side /close or /logout API call.

A server side background thread will release phantom Connections that were not closed by the client side.

Therefore, it is important for client applications to explicitly and systematically call /logout API before the application exits, in order to avoid phantom Connections to persist for a period of time on the server.

Data transport

Transport format

AceQL transfers the least possible amount of meta-information:

  • Request parameters are transported in UTF-8 format
  • JSON format is used for data and class transport.

Content streaming and memory management

All requests are streamed:

  • Output requests (from the client side) are streamed directly from the socket to the server to avoid buffering any content body
  • Input responses (for the client side) are streamed directly from the socket to the server to efficiently read the response body

Large content (ResultSet, Blobs/Clobs…) is transferred using files. It is never loaded in memory. Streaming techniques are always used to read and write this content.

Managing temporary files

AceQL uses temporary files, these temporary files contain:

  • Contents of Result Sets
  • Contents of Blobs and Clobs

Temporary files are created to allow streaming and/or to allow the earliest possible release of SQL resources and network resources.

These temporary files are automatically cleaned (deleted) by AceQL on the server side.

If you want to ensure that temporary files will be cleaned, you can access the temporary directories:

  1. ResultSet data is dumped in user.home/.kawansoft/tmp directory

  2. The uploaded/downloaded Blob or Clob files are located in the directory defined by DatabaseConfigurator.getBlobsDirectory(). Default DefaultDatabaseConfigurator.getBlobsDirectory() implementation stores the Blob/Clob files in user.home/.aceql-server-root/username.


  • user.home = the user.home of the user that started the AceQL Web Server.

  • username = the username of the client user.

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