In the previuos blog I’ve made a Java class Grep that exports a method named doGrep(). I also supplied a Java test driver to test the Grep class. In this blog I will write the ALGOL program that takes the search text and directory as a parameter and calls the Java doGrep() method to do the actual work.
The utility JifGen has been run to generate the ALGOL include file that holds the definitions of the Java methods (GREP_INCL.ALG_M). I copied this ALGOL symbol to my MCP system as
My ALGOL program looks like this:
00004000% text: String parameter of the text to search for.
00005000% path: String parameter of file or directory to search.
00006000% recurse: Boolean, if TRUE all subdirectories will also be
00009000% Note: The Apache Software Licence applies to this code.
00013000$$ set level 2
00017000$$ INCLUDE JNI="*DIR/JRE6/JDK/INCLUDE/JNILIB/ALGOL ON DISK"
00019000 REAL ARRAY envEtc[0:JNI_MIN_ENV_ARRAY_SIZE+JNI_MIN_JVM_ARRAY_SIZE ];
00020000 ARRAY JNIEnv = envEtc;
00021000 ARRAY JavaVM[-JNI_MIN_ENV_ARRAY_SIZE] = envEtc;
00022000 ebcdic value array jvmOptions ("-cp ./grep.jar " 48"00");
00023000 ebcdic value array mcpOptions (48"00");
00024000 integer jvmRslt;
00025000 double returnArray;
00026000 ebcdic array param[0:299];
00027000 ebcdic array ax[0:119];
00028000 integer errorCode;
00029000 pointer pparam;
00029200 file lp(kind = printer);
00029400 ebcdic array line[0:132];
00031000$$ INCLUDE GREPJNI="GREP/SRC/INCLUDE/GREP_INCL"
00033000 procedure listHits(returnArray);
00034000 value returnArray;
00035000 double returnArray;
00038000 ebcdic array found[0:300];
00039000 integer foundLen;
00040000 double arrayElement;
00041000 integer returnLength;
00042000 integer i;
00044000 returnLength := JNI_GET_ARRAY_LENGTH(JNIEnv, returnArray);
00046000 for i := 0 step 1 until (returnLength - 1) do
00048000 replace found by " " for 300;
00049000 foundLen := 300;
00050000 arrayElement := JNI_GET_OBJECT_ARRAY_ELEMENT
00051000 (JNIEnv, returnArray, i);
00053000 (JNIEnv, arrayElement, found, 0, foundLen);
00054000 if foundLen > 0 then
00056000 write(lp, *, found);
00059000 end of listHits;
00061000 if (size(arguments) * 6) > 300 then
00063000 resize(param, size(arguments) * 6, DISCARD);
00065000 replace pparam:param by pointer(arguments)
00066000 for size(arguments) * 6 until = 48"00";
00068000 % Initialize the Java Virtual Machine
00069000 jvmRslt := JNI_CREATE_JAVA_VM_STAR(JavaVM, JNIEnv,
00072100 if jvmRslt < 0 then
00072300 replace line by " " for 132;
00072400 replace line by "Result from JNI_CREATE_JAVA_VM_STAR: ",
00072500 jvmRslt for * digits;
00072600 write(lp, 132, line);
00074000 returnArray := GREP__GREP_DO_GREP(param,
00075000 0, offset(pparam));
00076000 if JNI_Check_Exception(JNIEnv) then
00078000 errorCode := JNI_GET_LAST_ERROR(JNIEnv);
00079000 replace ax by "JNI Exception: Error code = ",
00080000 errorCode for * digits, 48"00";
00085000end of grep.
Line 17000 includes the variables and procedure declarations that are necessary to communicate via JNI. It needs to be included before the include of the generated
GREP/SRC/INCLUDE/GREP_INCL. The lines 19000 – 21000 declare some arrays that the generated ALGOL file needs. The comments at the top of the generated include file remind you of this.
Lines 22000 and 23000 define parameter strings that need to be supplied to the
JNI_CREATE_JAVA_VM_STAR procedure (line 69000). This procedure will start a Java Virtual Machine on the JProcessor. The array jvmOptions sets the CLASSPATH of the JVM. In this program I have hardcoded the CLASSPATH relative to the CURRENTDIRECTORY attribute of the program. I a production system you would probably get these parameters from a configuration file.
INIALIZE_GREP_ in line 73000 results in a call (via
GREP/SRC/INCLUDE/GREP_INCL) of the
JAVAJNILIB library procdeure
JNI_FIND_CLASS_E. This procedure returns a handle to the Grep class.
Since I've made the doGrep() method a static method, I don't need to create an instance of the Grep class. I find this makes the ALGOL code less complicated. In a production system that I built, I defined a single class to interface between Java and ALGOL. A call to a static method in this class creates a single instance of a Manager class, the Manager class in turn, instantiates other objects as needed. This scheme can work because a JVM is dedicated to one program stack.
In line 74000, the actual
doGrep method is called. The parameter
param is an EBCDIC array that contains the arguments for doGrep. The next parameter,
0, is the offset into the
param array where the actual arguments start. The last parameter gives the length, in characters, of the arguments string. The
GREP__GREP_DO_GREP procedure in the generated include file wraps the actual, more complex, JNI call.
I started a test using the WFL below:
00000100BEGIN JOB WFL/GREP;
00000350 "-r grep /-/user/usercode/ruud/grep/src");
00000400 LIBRARY JAVAVM(LIBACCESS = BYTITLE,
00000500 TITLE=*DIR/JRE6/BIN/JAVAPROXYLIB ON DISK);
CURRENTDIRECTORY equation is, apparently, just for the GREP/GREPDRIVER program, it is not propagated to the Java Virtual Machine. That means that the path to directory to be searched by Grep must be an absolute path, it cannot be relative to the
I also got a message
“JAVAHOMEPATH not provided; JRE location extracted from proxy name (/-/DISK/DIR/JRE6).”. This message comes from the program
*SYSTEM/JAVAFILE, which is used by the JVM to access the MCP file system. Adding a file equation
FILE JAVAHOMEPATH(PATHNAME="/-/DISK/DIR/JRE6"); did not get rid of the message. But using the path from the PROXYLIB is just fine.
When I ran my test WFL, much to my surprise, I didn't get any results back. I figured the
JNI_CREATE_JAVA_VM_STAR failed, that's why I added the code in lines 72300 – 72600. But there was no problem there, nor was there a problem in the
GREP__GREP_DO_GREP call. Wouldn't it be nice if I could debug my Java code now. Well, I could, the way to do that was obvious: Just insert the debug arguments
at the beginning of the
jvmOptions array and I could connect my Netbeans to the JVM under test. Stepping through the
doGrep() Java code, the problem jumped right at me. The
param.split(“ “) method splits the parameter string using a single space as a token separator, but my test job has two spaces between “grep” and “/-/user/....”. I have now changed the regular expression in the param.split to “ +”, telling the split to use one or more spaces to separate the string.