1 BUILDING A SIMPLE HTTP-TO-Z3950 GATEWAY USING YAZ4J AND TOMCAT
2 ==============================================================
4 [Yaz4J](http://www.indexdata.com/yaz4j) is a wrapper library over the
5 client-specific parts of YAZ, a C-based Z39.50 toolkit, and allows you to use
6 the ZOOM API directly from Java. Initial version of Yaz4j has been written
7 by Rob Styles from [Talis][http://www.talis.com] and the project is now
8 developed and maintained at IndexData.
9 [ZOOM](http://zoom.z3950.org/api/zoom-1.4.html) is a relatively straightforward
10 API and with a few lines of code you can write a basic application that can
11 establish connection to a Z39.50 server.
12 Here we will try to build a very simple HTTP-to-Z3950 gateway using yaz4j and
13 the Java Servlet technology.
15 ## COMPILING AND INSTALLING YAZ4J
17 Yaz4j is still an experimental piece of software and as such is not distributed
18 via Index Data's public Debian Apt repository and there is no Windows build (yet)
19 either. While it is possible to use the pre-built Linux binaries, users of
20 other OSes will have to compile yaz4j from source. No need to worry (yet) - the
21 process of compiling yaz4j is quite simple and we will be up and running in no
24 As a prerequisite, to complete th build process you will need JDK, Maven, Swig
25 and Yaz (development package) installed on your machine. On Debian/Ubuntu you
26 can get those easily via apt:
28 apt-get install sun-java6-jdk maven2 libyaz3-dev swig
31 The Yaz4j's source code can be checked-out out from our
32 [Git repository](http://git.indexdata.com/?p=yaz4j.git;a=summary), and assuming
33 you have Git installed on your machine you can do that with:
35 git clone git://git.indexdata.com/yaz4j
37 The compilation of both native and Java source code is controlled by Maven2,
38 to build the library, invoke the following commands:
43 That's it. If the build has completed successfully you end up with two files:
44 os-independent jar archive with Java ZOOM API classes
45 (yaz4j/any/target/yaz4j-any-VERSION.jar) and os-dependent shared library
46 (yaz4j/linux/target/libyaz4j.so or yaz4j/win32/target/yaz4j.dll) that contains
47 all necessary JNI "glue" to make the native calls possible from Java. If we were
48 writing a command line Java application, like any other external Java library,
49 yaz4j-any-VERSION.jar would have to be placed on your application classpath
50 and the native, shared library would have to be added to your system shared
51 library path (LD_LIBRARY_PATH on linux, PATH on Windows) or specified as a
52 Java system property (namely the java.library.path) just before your
53 application is executed:
55 java -cp /path/to/yaz4j-*.jar -Djava.library.path=/path/to/libyaz4j.so MyApp
57 ## SETTING UP THE DEVELOPMENT ENVIRONMENT
59 Setting up a development/runtime environment for a web (servlet) application is
60 a bit more complicated. First, you are not invoking the JVM directly, but the
61 servlet container (e.g Tomcat) run-script is doing that for you. At this
62 point the shared library (so or dll) has to be placed on the servlet container's
63 shared libraries load path. Unless your library is deployed to the standard
64 system location for shared libs (`/usr/lib` on Linux) or it's location is
65 already added to the path, the easiest way to do this in Tomcat is by editing
66 (create it if it does not exist) the `CATALINA_HOME/bin/setenv.sh` (setenv.bat
67 on Windows) script and putting the following lines in there:
69 LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/path/to/libyaz4j.so
70 export LD_LIBRARY_PATH
72 on Windows (though no Windows build is yet provided)
74 set PATH=%PATH;X:\path\to\yaz4j.dll
76 That's one way of doing it, another would be to alter the standard set of
77 arguments passed to the JVM before the Tomcat starts and add
78 `-Djava.library.path=/path/to/lib there`. Depending on a situation this might
79 be preferable/easier (on Debian/Ubuntu you can specify JVM arguments in the
80 `/etc/default/tomcat6` file).
82 With the shared library installed we need to install the pure-Java yaz4j-any*jar
83 with ZOOM API classes by placing it in Tomcat's `lib` directory
84 (CATALINA_HOME/lib). As this library makes the Java System call to load the
85 native library into the JVM you cannot simply package it along with your web
86 application (inside the .war file) - it would try to load the library each time
87 you deploy the webapp and all consecutive deployments would fail.
89 ## WRITING A SERVLET-BASED GATEWAY
91 With your servlet environment set up all that is left is to write the actual
92 application (peanuts :)). At IndexData we use Maven for managing builds of our
93 Java software components but Maven is also a great tool for quickly starting up
94 a project. To generate a skeleton for our webapp use the Maven archetype plugin:
96 mvn -DarchetypeVersion=1.0.1 -Darchetype.interactive=false -DarchetypeArtifactId=webapp-jee5 -DarchetypeGroupId=org.codehaus.mojo.archetypes -Dpackage=com.indexdata.zgate -DgroupId=com.indexdata -DartifactId=zgate archetype:generate --batch-mode
98 This will generate a basic webapp project structure:
121 Maven has already added basic JEE APIs for web development as the project
122 dependencies, we need to do the same for yaz4j, so edit the `pom.xml` and
123 add the following lines in the `dependencies` section:
125 <blockcode type="xml">
128 <groupId>org.yaz4j</groupId>
129 <artifactId>yaz4j-any</artifactId>
130 <version>VERSION</version>
131 <scope>provided</scope>
136 It's crucial that the scope of this dependency is set to `provided` otherwise
137 the library would end up packaged in the .war archive and we don't want that.
139 The implementation of our simple gateway will be contained in a single servlet -
140 `ZGateServlet` - which we need to place under `src/main/webapp/com/indexdata/zgate.`
141 The gateway will work by answering HTTP GET requests and will be controlled
142 solely by HTTP parameters, the servlet doGet method is shown below:
144 <blockcode type="java">
146 protected void doGet(HttpServletRequest request, HttpServletResponse response)
147 throws ServletException, IOException {
148 String zurl = request.getParameter("zurl");
149 if (zurl == null || zurl.isEmpty()) { response.sendError(400, "Missing parameter 'zurl'"); return; }
151 String query = request.getParameter("query");
152 if (query == null || query.isEmpty()) { response.sendError(400, "Missing parameter 'query'"); return; }
154 String syntax = request.getParameter("syntax");
155 if (syntax == null || syntax.isEmpty()) { response.sendError(400, "Missing parameter 'syntax'"); return; }
158 if (request.getParameter("maxrecs") != null && !request.getParameter("maxrecs").isEmpty()) {
160 maxrecs = Integer.parseInt(request.getParameter("maxrecs"));
161 } catch (NumberFormatException nfe) {
162 response.sendError(400, "Malformed parameter 'maxrecs'");
167 response.getWriter().println("SEARCH PARAMETERS");
168 response.getWriter().println("zurl: " + zurl);
169 response.getWriter().println("query: " + query);
170 response.getWriter().println("syntax: " + syntax);
171 response.getWriter().println("maxrecs: " + maxrecs);
172 response.getWriter().println();
174 Connection con = new Connection(zurl, 0);
175 con.setSyntax(syntax);
178 ResultSet set = con.search(query, Connection.QueryType.PrefixQuery);
179 response.getWriter().println("Showing " + maxrecs + " of " +set.getSize());
180 response.getWriter().println();
181 for(int i=0; i<set.getSize() && i<maxrecs; i++) {
182 Record rec = set.getRecord(i);
183 response.getWriter().print(rec.render());
185 } catch (ZoomException ze) {
186 throw new ServletException(ze);
194 With the code in-place we can try to compile the project:
198 If all is OK, the next step is to register our servlet and map it to an URL in
199 src/main/webapp/WEB-INF/web.xml:
201 <blockcode type="xml">
204 <servlet-name>ZgateServlet</servlet-name>
205 <servlet-class>com.indexdata.zgate.ZgateServlet</servlet-class>
208 <servlet-name>ZgateServlet</servlet-name>
209 <url-pattern>/zgate</url-pattern>
214 On top of that, we will also make sure that our servlet is automatically
215 triggered when accessing the root path of our application:
217 <blockcode type="xml">
220 <welcome-file>zgate</welcome-file>
221 <welcome-file>index.jsp</welcome-file>
226 Now we are ready to build our webapp:
230 The resulting .war archive is located under `target/zgate.war`, we can deploy
231 it on tomcat (e.g by using the /admin Tomcat admin console) and test by issuing
232 the follwoing request with your browser or curl
233 (assuming Tomcat is running on localhost:8080):
235 http://localhost:8080/zgate/?zurl=z3950.loc.gov:7090/voyager&query=@attr%201=7%200253333490&syntax=usmarc
238 That's it! You just build yourself a HTTP-to-Z3950 gateway! Just be careful
239 with exposing it to the outside world - it's not very secure and could be
240 easily exploited. The source code and the gateway's Maven project is available
241 in the Yaz4j's Git repository under examples/zgate. In the meantime, IndexData
242 is working on a Debian/Ubuntu package to make the installation of Yaz4j and
243 Tomcat configuration greatly simplified - so stay tuned!. If you are interested
244 in Windows support - e.g. Visual Studio based build or an installer - please