Specify and document value for environment variable for loading native library in Java bindings (#5477)

* limit range of environment variable for loading the native library in Java to "true".

This change specifies the range of values that are allowed to set the environment
variable "z3.skipLibraryLoad".
Only the value "true" (in upper-, lower-, and mixed-case is accepted as valid value.
Other values, such as "false", "0", "1", "foo", an empty or a missing value are
evaluated to "false" and cause the default loading of the native library.

* adding documentation about environment variable for (not) loading the native library in Java.

This is a follow-up commit for #4667 to provide a publicly visible documentation.

Author: kfriedberger

examples/java/README

@@ -12,3 +12,9 @@ On Linux and FreeBSD, we must use
    LD_LIBRARY_PATH=. java -cp com.microsoft.z3.jar:. JavaExample
 On macOS, the corresponding option is DYLD_LIBRARY_PATH:
    DYLD_LIBRARY_PATH=. java -cp com.microsoft.z3.jar:. JavaExample  
+
+By default, Z3 Java bindings are automatically loading the required native library for Z3 from the default library path.
+In certain environments, depending on the developing process, the Z3 library is not available in the given library path.
+To disable the automated loading process, the user can set the environment variable "z3.skipLibraryLoad=true".
+In that case, the calling application should directly load the corresponding libraries before any interaction with Z3.
+

scripts/update_api.py

@@ -545,7 +545,7 @@ def mk_java(java_dir, package_name):
     java_native.write('  public static native void setInternalErrorHandler(long ctx);\n\n')
 
     java_native.write('  static {\n')
-    java_native.write('    if (null == System.getProperty("z3.skipLibraryLoad")) {\n')
+    java_native.write('    if (!Boolean.parseBoolean(System.getProperty("z3.skipLibraryLoad"))) {\n')
     java_native.write('      try {\n')
     java_native.write('        System.loadLibrary("z3java");\n')
     java_native.write('      } catch (UnsatisfiedLinkError ex) {\n')