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<!DOCTYPE chapter SYSTEM "chapter.dtd">

<chapter>
  <header>
    <copyright>
      <year>1999</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
    
    </legalnotice>

    <title>IDL to Java language Mapping</title>
    <prepared></prepared>
    <docno></docno>
    <date>98-09-24</date>
    <rev>A</rev>
    <file>ch_java.xml</file>
  </header>

  <section>
    <title>Introduction</title>
    <p>This chapter describes the mapping of OMG IDL constructs to the Java
      programming language for the generation of native Java - Erlang  
      communication. </p>
    <p>This language mapping defines the following:</p>
    <list type="bulleted">
      <item>
        <p>All OMG IDL basic types</p>
      </item>
      <item>
        <p>All OMG IDL constructed types</p>
      </item>
      <item>
        <p>References to constants defined in OMG IDL</p>
      </item>
      <item>
        <p>Invocations of operations, including passing of
          parameters and receiving of result</p>
      </item>
      <item>
        <p>Access to attributes</p>
      </item>
    </list>
  </section>

  <section>
    <title>Specialties in the Mapping</title>

    <section>
      <title>Names Reserved by the Compiler</title>
      <p>The IDL compiler reserves all identifiers starting with
        <c>OE_</c> and <c>oe_</c> for internal use.</p>
    </section>
  </section>

  <section>
    <title>Basic OMG IDL Types</title>
    <p>The mapping of basic types are according to the standard. All basic types have 
      a special Holder class.</p>
    <table>
      <row>
        <cell align="left" valign="middle">OMG IDL type</cell>
        <cell align="left" valign="middle">Java type</cell>
      </row>
      <row>
        <cell align="left" valign="middle">float</cell>
        <cell align="left" valign="middle">float</cell>
      </row>
      <row>
        <cell align="left" valign="middle">double</cell>
        <cell align="left" valign="middle">double</cell>
      </row>
      <row>
        <cell align="left" valign="middle">short</cell>
        <cell align="left" valign="middle">short</cell>
      </row>
      <row>
        <cell align="left" valign="middle">unsigned short</cell>
        <cell align="left" valign="middle">short</cell>
      </row>
      <row>
        <cell align="left" valign="middle">long</cell>
        <cell align="left" valign="middle">int</cell>
      </row>
      <row>
        <cell align="left" valign="middle">long long</cell>
        <cell align="left" valign="middle">long</cell>
      </row>
      <row>
        <cell align="left" valign="middle">unsigned long</cell>
        <cell align="left" valign="middle">long</cell>
      </row>
      <row>
        <cell align="left" valign="middle">unsigned long long</cell>
        <cell align="left" valign="middle">long</cell>
      </row>
      <row>
        <cell align="left" valign="middle">char</cell>
        <cell align="left" valign="middle">char</cell>
      </row>
      <row>
        <cell align="left" valign="middle">wchar</cell>
        <cell align="left" valign="middle">char</cell>
      </row>
      <row>
        <cell align="left" valign="middle">boolean</cell>
        <cell align="left" valign="middle">boolean</cell>
      </row>
      <row>
        <cell align="left" valign="middle">octet</cell>
        <cell align="left" valign="middle">octet</cell>
      </row>
      <row>
        <cell align="left" valign="middle">string</cell>
        <cell align="left" valign="middle">java.lang.String</cell>
      </row>
      <row>
        <cell align="left" valign="middle">wstring</cell>
        <cell align="left" valign="middle">java.lang.String</cell>
      </row>
      <row>
        <cell align="left" valign="middle">any</cell>
        <cell align="left" valign="middle">Any</cell>
      </row>
      <row>
        <cell align="left" valign="middle">long double</cell>
        <cell align="left" valign="middle">Not supported</cell>
      </row>
      <row>
        <cell align="left" valign="middle">Object</cell>
        <cell align="left" valign="middle">Not supported</cell>
      </row>
      <row>
        <cell align="left" valign="middle">void</cell>
        <cell align="left" valign="middle">void</cell>
      </row>
      <tcaption>OMG IDL basic types</tcaption>
    </table>
  </section>

  <section>
    <title>Constructed OMG IDL Types</title>
    <p>All constructed types are according to the standard with three (3) major exceptions.</p>
    <p></p>
    <list type="bulleted">
      <item>
        <p>The IDL Exceptions are not implemented in this Java mapping.</p>
        <p></p>
      </item>
      <item>
        <p>The functions used for read/write to streams, defined in <c>Helper</c> functions
          are named unmarshal (instead for read) and marshal (instead for write).  </p>
        <p></p>
      </item>
      <item>
        <p>The streams used in <c>Helper</c> functions are <c>OtpInputStream</c> for 
          input and <c>OtpOutputStream</c> for output.</p>
        <p></p>
      </item>
    </list>
  </section>

  <section>
    <title>Mapping for Constants</title>
    <p>Constants are mapped according to the standard.</p>
  </section>

  <section>
    <title>Invocations of Operations</title>
    <p>Operation invocation is implemented according to the standard.
      The implementation is in the class <c><![CDATA[_<nterfacename>Stub.java]]></c> which implements 
      the interface in <c><![CDATA[<nterfacename>.java]]></c>.</p>
    <code type="none">
test._iStub client;

client.op(10);
    </code>

    <section>
      <title>Operation Implementation</title>
      <p>The server is implemented through extension of the class 
        <c><![CDATA[_<nterfacename>ImplBase.java]]></c> and implementation of all the methods in the 
        interface.</p>
      <code type="none">
public class server extends test._iImplBase {
  
  public void op(int i) throws java.lang.Exception {
    System.out.println("Received call op()");
    o.value = i;
    return i;
  }

}
      </code>
    </section>
  </section>

  <section>
    <title>Exceptions</title>
    <p>While exception mapping is not implemented, the stubs will
      generate some Java exceptions in case of operation failure.
      No exceptions are propagated through the communication.</p>
  </section>

  <section>
    <title>Access to Attributes</title>
    <p>Attributes are supported according to the standard.</p>
  </section>

  <section>
    <title>Summary of Argument/Result Passing for Java</title>
    <p>All types (<c>in</c>, <c>out</c> or <c>inout</c>) of user defined parameters are supported
      in the Java mapping. This is also the case in the Erlang mappings but <em>not</em> in the C 
      mapping. <c>inout</c> parameters are not supported in the C mapping so if you are going to 
      do calls to or from a C program <c>inout</c> cannot be used in the IDL specifications.</p>
    <p><c>out</c> and <c>inout</c> parameters must be of Holder types. There is a jar file ( <c>ic.jar</c>) 
      with Holder classes for the basic types in the <c>ic</c> application. This library is in the directory
      <c><![CDATA[$OTPROOT/lib/ic_<version number>/priv]]></c>.</p>
  </section>

  <section>
    <title>Communication Toolbox</title>
    <p>The generated client and server stubs use the classes
      defined in the <c>jinterface</c> package to communicate 
      with other nodes.
      The most important classes are :</p>
    <list type="bulleted">
      <item>
        <p><c>OtpInputStream</c> which is the stream class used for incoming message storage</p>
        <p></p>
      </item>
      <item>
        <p><c>OtpOutputStream</c> which is the stream class used for outgoing message storage</p>
        <p></p>
      </item>
      <item>
        <p><c>OtpErlangPid</c> which is the process identification class used to identify processes inside
          a java node.</p>
        <p>The recommended constructor function for the OtpErlangPid is 
          <c>OtpErlangPid(String node, int id, int serial, int creation)</c> where :</p>
        <p></p>
        <list type="bulleted">
          <item>
            <p><c>String node</c>, is the name of the node where this process runs.</p>
            <p></p>
          </item>
          <item>
            <p><c>int id</c>, is the identification number for this identity.</p>
            <p></p>
          </item>
          <item>
            <p><c>int serial</c>, internal information, must be an 18-bit integer.</p>
            <p></p>
          </item>
          <item>
            <p><c>int creation</c>, internal information, must have value in range 0..3.</p>
            <p></p>
          </item>
        </list>
      </item>
      <item>
        <p><c>OtpConnection</c> which is used to define a connection between nodes.</p>
        <p>While the connection object is stub side constructed in client stubs, it is
          returned after calling the <c>accept</c> function from an OtpErlangServer object
          in server stubs.
          The following methods used for node connection :</p>
        <p></p>
        <list type="bulleted">
          <item>
            <p><c>OtpInputStream receiveBuf()</c>, which returns the incoming streams that
              contain the message arrived.</p>
            <p></p>
          </item>
          <item>
            <p><c>void sendBuf(OtpErlangPid client, OtpOutputStream reply)</c>, which sends
              a reply message (in an OtpOutputStream form) to the client node.</p>
            <p></p>
          </item>
          <item>
            <p><c>void close()</c>, which closes a connection.</p>
            <p></p>
          </item>
        </list>
      </item>
      <item>
        <p><c>OtpServer</c> which is used to define a server node.</p>
        <p>The recommended constructor function for the OtpServer is :</p>
        <p></p>
        <list type="bulleted">
          <item>
            <p><c>OtpServer(String node, String cookie)</c>. where :</p>
            <p></p>
            <list type="bulleted">
              <item>
                <p><c>node</c> is the requested name for the new java node, 
                  represented as a String object.</p>
                <p></p>
              </item>
              <item>
                <p><c>cookie</c> is the requested cookie name for the new java node, 
                  represented as a String object.</p>
                <p></p>
              </item>
            </list>
          </item>
        </list>
        <p>The following methods used for node registration and connection acceptance :</p>
        <p></p>
        <list type="bulleted">
          <item>
            <p><c>boolean publishPort()</c>, which registers the server node to <c>epmd</c> daemon.</p>
            <p></p>
          </item>
          <item>
            <p><c>OtpConnection accept()</c>, which waits for a connection and returns the 
              OtpConnection object which is unique for each client node.</p>
            <p></p>
          </item>
        </list>
      </item>
    </list>
  </section>

  <section>
    <title>The Package com.ericsson.otp.ic</title>
    <p>The package <seealso marker="java/com/ericsson/otp/ic/package-summary">com.ericsson.otp.ic</seealso> 
      contains a number of java classes specially designed for the IC generated java-back-ends :</p>
    <list type="bulleted">
      <item>
        <p>Standard java classes defined through OMG-IDL java mapping :</p>
        <list type="bulleted">
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/BooleanHolder">BooleanHolder</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/ByteHolder">ByteHolder</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/CharHolder">CharHolder</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/ShortHolder">ShortHolder</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/IntHolder">IntHolder</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/LongHolder">LongHolder</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/FloatHolder">FloatHolder</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/DoubleHolder">DoubleHolder</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/StringHolder">StringHolder</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/Any">Any</seealso>,
              <seealso marker="java/com/ericsson/otp/ic/AnyHelper">AnyHelper</seealso>,
              <seealso marker="java/com/ericsson/otp/ic/AnyHolder">AnyHolder</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/TypeCode">TypeCode</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/TCKind">TCKind</seealso></p>
            <p></p>
          </item>
        </list>
      </item>
      <item>
        <p>Implementation-dependant classes :</p>
        <list type="bulleted">
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/Environment">Environment</seealso></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/Holder">Holder</seealso></p>
            <p></p>
          </item>
        </list>
      </item>
      <item>
        <p>Erlang compatibility classes :</p>
        <list type="bulleted">
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/Pid">Pid</seealso>,
              <seealso marker="java/com/ericsson/otp/ic/PidHelper">PidHelper</seealso>,
              <seealso marker="java/com/ericsson/otp/ic/PidHolder">PidHolder</seealso></p>
            <p>The Pid class originates from <c>OtpErlangPid</c> and is used to 
              represent the Erlang built-in <c>pid</c> type, a process's identity.
              PidHelper and PidHolder are helper respectively holder classes for Pid.</p>
            <p></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/Ref">Ref</seealso>,
              <seealso marker="java/com/ericsson/otp/ic/RefHelper">RefHelper</seealso>,
              <seealso marker="java/com/ericsson/otp/ic/RefHolder">RefHolder</seealso></p>
            <p>The Ref class originates from <c>OtpErlangRef</c> and is used to 
              represent the Erlang built-in <c>ref</c> type, an Erlang reference.
              RefHelper and RefHolder are helper respectively holder classes for Ref.</p>
            <p></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/Port">Port</seealso>,
              <seealso marker="java/com/ericsson/otp/ic/PortHelper">PortHelper</seealso>,
              <seealso marker="java/com/ericsson/otp/ic/PortHolder">PortHolder</seealso></p>
            <p>The Port class originates from <c>OtpErlangPort</c> and is used to 
              represent the Erlang built-in <c>port</c> type, an Erlang port.
              PortHelper and PortHolder are helper respectively holder classes for Port.</p>
            <p></p>
          </item>
          <item>
            <p><seealso marker="java/com/ericsson/otp/ic/Term">Term</seealso>,
              <seealso marker="java/com/ericsson/otp/ic/TermHelper">TermHelper</seealso>,
              <seealso marker="java/com/ericsson/otp/ic/TermHolder">TermHolder</seealso></p>
            <p>The Term class originates from <c>Any</c> and is used to 
              represent the Erlang built-in <c>term</c> type, an Erlang term.
              TermHelper and TermHolder are helper respectively holder classes for Term.</p>
            <p></p>
          </item>
        </list>
        <p>To use the Erlang build-in classes, you will have to include the file <c>erlang.idl</c>
          located under <c>$OTPROOT/lib/ic/include</c>.</p>
      </item>
    </list>
  </section>

  <section>
    <title>The Term Class</title>
    <p>The <c>Term</c> class is intended to represent the Erlang term generic type.
      It extends the <c>Any</c> class and it is basically used in the same way as
      in the Any type.</p>
    <p>The big difference between Term and Any is the use of <c>guard</c> methods
      instead of <c>TypeCode</c> to determine the data included in the Term.
      This is especially true when the Term's value class cannot be 
      determined at compilation time. The guard methods found in Term :</p>
    <list type="bulleted">
      <item>
        <p><c>boolean isAtom()</c> returns <c>true</c> if the Term is an OtpErlangAtom, <c>false</c> otherwise</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean isConstant()</c> returns <c>true</c> if the Term is neither an OtpErlangList nor an OtpErlangTuple, <c>false</c> otherwise</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean isFloat()</c> returns <c>true</c> if the Term is an OtpErlangFloat, <c>false</c> otherwise</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean isInteger()</c> returns <c>true</c> if the Term is an OtpErlangInt, <c>false</c> otherwise</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean isList()</c> returns <c>true</c> if the Term is an OtpErlangList, <c>false</c> otherwise</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean isString()</c> returns <c>true</c> if the Term is an OtpErlangString, <c>false</c> otherwise</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean isNumber()</c> returns <c>true</c> if the Term is an OtpErlangInteger or an OtpErlangFloat, <c>false</c> otherwise</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean isPid()</c> returns <c>true</c> if the Term is an OtpErlangPid or Pid, <c>false</c> otherwise</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean isPort()</c> returns <c>true</c> if the Term is an OtpErlangPort or Port, <c>false</c> otherwise</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean isReference()</c> returns <c>true</c> if the Term is an OtpErlangRef, <c>false</c> otherwise</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean isTuple()</c> returns <c>true</c> if the Term is an OtpErlangTuple, <c>false</c> otherwise</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean isBinary()</c> returns <c>true</c> if the Term is an OtpErlangBinary, <c>false</c> otherwise</p>
        <p></p>
      </item>
    </list>
  </section>

  <section>
    <title>Stub File Types</title>
    <p>For each interface, three (3) stub/skeleton files are generated :</p>
    <list type="bulleted">
      <item>
        <p>A java interface file, named after the idl interface.</p>
        <p></p>
      </item>
      <item>
        <p>A client stub file, named after the convention  <c><![CDATA[_< interface name >Stub]]></c> 
          which implements the java interface. Example : <c>_stackStub</c>.java</p>
        <p></p>
      </item>
      <item>
        <p>A server stub file, named after the convention  <c><![CDATA[_< interface name >ImplBase]]></c> 
          which implements the java interface. Example : <c>_stackImplBase</c>.java</p>
        <p></p>
      </item>
    </list>
  </section>

  <section>
    <title>Client Stub Initialization, Methods Exported</title>
    <p>The recommended constructor function for client stubs accepts four (4) parameters :</p>
    <p></p>
    <list type="bulleted">
      <item>
        <p><c>String selfNode</c>, the node identification name to be used in the new
          client node.</p>
        <p></p>
      </item>
      <item>
        <p><c>String peerNode</c>, the node identification name where the client process is running.</p>
        <p></p>
      </item>
      <item>
        <p><c>String cookie</c>, the cookie to be used.</p>
        <p></p>
      </item>
      <item>
        <p><c>Object server</c>, where the java Object can be one of:</p>
        <p></p>
        <list type="bulleted">
          <item>
            <p><c>OtpErlangPid</c>, the server's process identity under the node where the server 
              process is running.</p>
            <p></p>
          </item>
          <item>
            <p><c>String</c>, the server's registered name under the node where the server 
              process is running.</p>
            <p></p>
          </item>
        </list>
      </item>
    </list>
    <p>The methods exported from the generated client stub are :</p>
    <p></p>
    <list type="bulleted">
      <item>
        <p><c>void __disconnect()</c>, which disconnects the server connection.</p>
        <p></p>
      </item>
      <item>
        <p><c>void __reconnect()</c>, which disconnects the server connection if open,
          and then connects to the same peer.</p>
        <p></p>
      </item>
      <item>
        <p><c>void __stop()</c>, which sends the standard stop termination call.
          When connected to an Erlang server, the server will be terminated.
          When connected to a java server, this will set a stop flag that 
          denotes that the server must be terminated.</p>
        <p></p>
      </item>
      <item>
        <p><c>com.ericsson.otp.erlang.OtpErlangRef __getRef()</c>, will return the message reference
          received from a server that denotes which call it is referring to.
          This is useful when building asynchronous clients.</p>
        <p></p>
      </item>
      <item>
        <p><c>java.lang.Object __server()</c>, which returns the server for the current connection.</p>
        <p></p>
      </item>
    </list>
  </section>

  <section>
    <title>Server Skeleton Initialization, Server Stub Implementation, Methods Exported</title>
    <p>The constructor function for server skeleton accepts no parameters.</p>
    <p>The server skeleton file contains a server <c>switch</c> which
      decodes messages from the input stream and calls implementation
      (<c>callback</c>) functions.
      As the server skeleton is declared <c>abstract</c>, the application 
      programmer will have to create a stub class that <c>extends</c> the
      skeleton file. In this class, all operations defined in the interface
      class, generated under compiling the idl file, are implemented.</p>
    <p>The server skeleton file exports the following methods:</p>
    <p></p>
    <list type="bulleted">
      <item>
        <p><c>OtpOutputStrem invoke(OtpInputStream request)</c>, where the input
          stream <c>request</c> is unmarshalled, the implementation function is called
          and a reply stream is marshalled.</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean __isStopped()</c>, which returns true if a stop message is received.
          The implementation of the stub should always check if such a message is received
          and terminate if so.</p>
        <p></p>
      </item>
      <item>
        <p><c>boolean __isStopped(com.ericsson.otp.ic.Environment)</c>, which returns true if 
          a stop message is received for a certain Environment and Connection.
          The implementation of the stub should always check if such a message is received
          and terminate if so.</p>
        <p></p>
      </item>
      <item>
        <p><c>OtpErlangPid __getCallerPid()</c>, which returns the caller identity for the latest call.</p>
        <p></p>
      </item>
      <item>
        <p><c>OtpErlangPid __getCallerPid(com.ericsson.otp.ic.Environment)</c>, which returns the caller 
          identity for the latest call on a certain Environment.</p>
        <p></p>
      </item>
      <item>
        <p><c>java.util.Dictionary __operations()</c>, which returns the operation dictionary which
          holds all operations supported by the server skeleton.</p>
        <p></p>
      </item>
    </list>
  </section>

  <section>
    <title>A Mapping Example</title>
    <p>      <marker id="stack_idl"></marker>

      This is a small example of a simple stack. There are two
      operations on the stack, push and pop. The example shows some of the 
      generated files.</p>
    <code type="none">
// The source IDL file: stack.idl

struct s {
      long l;
      string s;
};

interface stack {
    void push(in s val);
    s pop();
};
    </code>
    <p>When this file is compiled it produces eight files. Three important files 
      are shown below.      <marker id="stack_serv"></marker>
</p>
    <p>The public interface is in <em>stack.java</em>.</p>
    <code type="none">

public interface stack {

/****
 * Operation "stack::push" interface functions 
 *
 */

    void push(s val) throws java.lang.Exception;

/****
 * Operation "stack::pop" interface functions 
 *
 */

    s pop() throws java.lang.Exception;

}
    </code>
    <p>For the IDL struct s three files are generated, a public class in <em>s.java</em>.</p>
    <code type="none">

final public class s {
   // instance variables
   public int l;
   public java.lang.String s;

   // constructors
   public s() {};
   public s(int _l, java.lang.String _s) {
     l = _l;
     s = _s;
   };

};
    </code>
    <p>A holder class in <em>sHolder.java</em> and a helper class in <em>sHelper.java</em>.
      The helper class is used for marshalling.</p>
    <code type="none">

public class sHelper {

   // constructors
   private sHelper() {};

   // methods
   public static s unmarshal(OtpInputStream in) 
      throws java.lang.Exception {
        :
        :
   };

   public static void marshal(OtpOutputStream out, s value) 
      throws java.lang.Exception {
        :
        :
   };

};
    </code>
  </section>

  <section>
    <title>Running the Compiled Code</title>
    <p>When using the generated java code you must have added 
      <c><![CDATA[$OTPROOT/lib/ic_<version number>/priv]]></c> and 
      <c><![CDATA[$OTPROOT/lib/jinterface_<version number>/priv]]></c> to your 
      <c>CLASSPATH</c> variable to get
      basic Holder types and the communication classes.</p>
  </section>
</chapter>

