139 lines
6.7 KiB
HTML
139 lines
6.7 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<META http-equiv="Content-Type" content="text/html; charset=utf-8">
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<LINK rel="stylesheet" type="text/css" href="../../../rzahg/ic.css">
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<title>Troubleshoot: Serialization and deserialization in Web services</title>
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</head>
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<BODY>
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<!-- Java sync-link -->
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<SCRIPT LANGUAGE="Javascript" SRC="../../../rzahg/synch.js" TYPE="text/javascript"></SCRIPT>
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<h2><A NAME="wstrbserialize">Troubleshoot: Serialization and deserialization in Web services</A></h2>
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<p>The following are problems you might encounter performing serialization
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and deserialization in Web services that are developed and implemented based
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on the Web Services for Java 2 platform Enterprise Edition (J2EE) specification.</p>
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<p><strong>Time zone information in deserialized java.util.Calendar is
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not as expected</strong></p>
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<p>When the client and server are based on Java code
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and a <tt>java.util.Calendar</tt> object is received, the time zone in the received <tt>java.util.Calendar</tt> instance
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might be different from that of the <tt>java.util.Calendar</tt> instance that
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was sent.</p>
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<p>This occurs because <tt>java.util.Calendar</tt> is encoded
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as an xsd:dateTime for transmission. An xsd:dateTime is required to encode
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the correct time (base time plus or minus a time zone offset), but is not
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required to preserve locale information, including the original time zone.</p>
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<p>The fact that the time zone for the current locale is not preserved needs to be
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accounted for when comparing Calendar instances. The <tt>java.util.Calendar </tt> class
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equals method checks that the time zones are the same when determining equality.
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Since the time zone in a deserialized Calendar instance might not match the
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current locale, the before and after comparison methods should be used to
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test that two Calendars refer to the same date and time as shown below:</p>
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<pre>
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java.util.Calendar c1 = ...// Date and time in time zone 1
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java.util.Calendar c2 = ...// Same date and equivalent time, but in time zone 2
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// c1 and c2 are not equal because their time zones are different
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if (c1.equals (c2)) System.out.println("c1 and c2 are equal");
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// but c1 and c2 do compare as "not before and not after" since they represent
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the same date and time
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if (!c1.after(c2) & !c1.before(c2) {
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System.out.println("c1 and c2 are equivalent");
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}</pre>
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<p><strong>Mixing Web services client and server bindings
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causes exceptions</strong></p>
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<p>Web Services for J2EE and Java API for XML-based
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remote procedure call (JAX-RPC) do not support "round-trip" mapping between
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Java code and a Web Services Description Language (WSDL) document for all
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Java types. For example, you cannot turn (serialize) a Java Date into XML
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code and then turn it back (deserialize) into a Java Date. It deserializes
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as Java Calendar.</p>
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<p>If you have a Java implementation that you create
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a WSDL document from, and you generate client bindings from the WSDL document,
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the client classes can be different from the server classes even though the
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client classes have the same package and class names. The Web service client
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classes must be kept separate from the Web service server classes. For example,
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do not place the Web service server bindings classes in a utility Java archive
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(JAR) file and then include a Web service client JAR file that references
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the same utility JAR file.</p>
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<p>If you do not keep the Web service client
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and server classes separate, a variety of exceptions can occur, depending
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on the Java classes used. The following is a sample stack trace error that
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can occur:</p>
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<pre>
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com.ibm.ws.webservices.engine.PivotHandlerWrapper TRAS0014I: The following exception was
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loggedjava.lang.NoSuchMethodError: com.ibm.wssvt.acme.websvcs.ExtWSPolicyData: method
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getStartDate()Ljava/util/Date; not found
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at com.ibm.wssvt.acme.websvcs.ExtWSPolicyData_Ser.addElements(ExtWSPolicyData_Ser.java: 210)
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at com.ibm.wssvt.acme.websvcs.ExtWSPolicyData_Ser.serialize (ExtWSPolicyData_Swer.java:29)
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at com.ibm.ws.webservices.engine.encoding.SerializationContextImpl.serializeActual
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(SerializationContextImpl.java 719)
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at com.ibm.ws.webservices.engine.encoding.SerializationContextImpl.serialize
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(SerializationContextImpl.java: 463)
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</pre>
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<p>The problem is caused by using an interface like the following for the Service
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Endpoint Interface in the service implementation:</p>
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<pre>
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package server:
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public interface Test_SEI extends java.rmi.Remote {
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public java.util.Calendar getCalendar () throws java.rmi.RemoteException;
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public java.util.Date getDate() throws java.rmi.RemoteException;
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}
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</pre>
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<p>When this interface is compiled and run through the <strong>Java2WSDL</strong> command-line
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tool, the WSDL document maps the methods as follows:</p>
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<pre>
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<wsdl:message name="getDateResponse">
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<wsdl:part name="getDateReturn" type="xsd:dateTime"/>
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</wsdl:message>
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<wsdl:message name="getCalendarResponse">
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<wsdl:part name="getCalendarReturn" type="xsd:dateTime"/>
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</wsdl:message>
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</pre>
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<p>The JAX-RPC mapping implemented by the <strong>Java2WSDL</strong> tool
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has mapped both <tt>java.util.Date</tt> and <tt>java.util.Calendar</tt> to
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the XML type xsd:dateTime. The next step is to use the generated WSDL file
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to create a client for the Web service. When you run the <strong>WSDL2Java</strong> command-line
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tool on the generated WSDL, the generated classes include a different version
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of server.Test_SEI, for example:</p>
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<pre>
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package server;
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public interface Test_SEI extends java.rmi.Remote {
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public java.util.Calendar getCalendar() throws java.rmi.RemoteException;
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public java.util.Date getDate() throws java.rmi.RemoteException;
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}
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</pre>
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<p><strong>Note:</strong> The client version of the <tt>service.Test_SEI</tt> interface
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is different from the server version in that both <tt>getCalendar</tt> and <tt>getDate</tt> methods
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return <tt>java.util.Calendar</tt>. The serialization and deserialization
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code that the client expects is the client version of the SEI. If the server
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version inadvertently appears in the client's CLASSPATH, at either compilation
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or execution time, an exception occurs.</p>
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<p>In addition to the<tt>NoSuchMethod</tt> error,
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the <tt>IncompatibleClassChangeError </tt>and <tt>ClassCastException </tt> can
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occur, however, almost any run-time exception can occur. The best practice
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is to be diligent about separating client Web services bindings classes from
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server Web services bindings classes. The client bindings classes and server
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bindings classes should never be placed in the same module and, if they are
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in the same application, should not have bindings classes in utility JAR files
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that are shared between modules.</p>
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</body>
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</html>
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