Problems with Android's UriMatcher

Question

In an answer to a previous question of mine someone indicated that there is some flakiness (for lack of a better word) inherent in the Android class UriMatcher. Can anyone pinpoint the known issues with UriMatcher? I'm designing a Content Provider that relies on UriMatcher to match my Uris correctly (as opposed to incorrectly I suppose). Are there workarounds to the known issues? Or is there a better strategy for matching Uris?

Example:

Here is the code setting my UriMatcher

private static final int MEMBER_COLLECTION_URI = 1;
private static final int MEMBER_SINGLE_URI = 2;
private static final int SUBMATERIAL_COLLECTION_URI = 3;
private static final int SUBMATERIAL_SINGLE_URI = 4;
private static final int JOBNAME_COLLECTION_URI = 5;
private static final int JOBNAME_SINGLE_URI = 6;
private static final int ALL_MEMBERS_URI = 7;
private static final int ALL_SUBMATERIAL_URI = 8;

static
{
        //return the job and fab for anything matching the provided jobName
        // JobNames/jobName
        uriMatcher.addURI(JobMetaData.AUTHORITY, "JobNames/*/",
                          JOBNAME_SINGLE_URI);
        //return a collection of members
        // jobName/member/attribute/value
        uriMatcher.addURI(JobMetaData.AUTHORITY, "*/member/*/*/",
                          MEMBER_COLLECTION_URI);
        //return a single member
        // jobName/member/memberNumber
        uriMatcher.addURI(JobMetaData.AUTHORITY, "*/member/*/",
                          MEMBER_SINGLE_URI);
        //return a collection of submaterial
        // jobName/submaterial/attribute/value
        uriMatcher.addURI(JobMetaData.AUTHORITY, "*/submaterial/*/*",
                          SUBMATERIAL_COLLECTION_URI);
        //return a single piece of submaterial
        // jobName/submaterial/GUID
        //GUID is the only way to uniquely identify a piece of submaterial    
        uriMatcher.addURI(JobMetaData.AUTHORITY, "*/submaterial/*",
                          SUBMATERIAL_SINGLE_URI);
        //Return everything in the member and submaterial tables
        //that has the provided attribute that matches the provided value
        // jobName/attribute/value
        //not currently used
        uriMatcher.addURI(JobMetaData.AUTHORITY, "JobNames/",
                          JOBNAME_COLLECTION_URI);
        //return all members in a job
        uriMatcher.addURI(JobMetaData.AUTHORITY, "*/members/",
                          ALL_MEMBERS_URI);

}

Add another Uri:

private static final int MEMBER_COLLECTION_URI = 1;
private static final int MEMBER_SINGLE_URI = 2;
private static final int SUBMATERIAL_COLLECTION_URI = 3;
private static final int SUBMATERIAL_SINGLE_URI = 4;
private static final int JOBNAME_COLLECTION_URI = 5;
private static final int JOBNAME_SINGLE_URI = 6;
private static final int ALL_MEMBERS_URI = 7;
private static final int ALL_SUBMATERIAL_URI = 8;
//ADDITIONAL URI
private static final int REVERSE_URI = 9;

static
{
        //return the job and fab for anything matching the provided jobName
        // JobNames/jobName
        uriMatcher.addURI(JobMetaData.AUTHORITY, "JobNames/*/",
                          JOBNAME_SINGLE_URI);
        //return a collection of members
        // jobName/member/attribute/value
        uriMatcher.addURI(JobMetaData.AUTHORITY, "*/member/*/*/",
                          MEMBER_COLLECTION_URI);
        //return a single member
        // jobName/member/memberNumber
        uriMatcher.addURI(JobMetaData.AUTHORITY, "*/member/*/",
                          MEMBER_SINGLE_URI);
        //return a collection of submaterial
        // jobName/submaterial/attribute/value
        uriMatcher.addURI(JobMetaData.AUTHORITY, "*/submaterial/*/*",
                          SUBMATERIAL_COLLECTION_URI);
        //return a single piece of submaterial
        // jobName/submaterial/GUID
        //GUID is the only way to uniquely identify a piece of submaterial    
        uriMatcher.addURI(JobMetaData.AUTHORITY, "*/submaterial/*",
                          SUBMATERIAL_SINGLE_URI);
        //Return everything in the member and submaterial tables
        //that has the provided attribute that matches the provided value
        // jobName/attribute/value
        //not currently used
        uriMatcher.addURI(JobMetaData.AUTHORITY, "JobNames/",
                          JOBNAME_COLLECTION_URI);
        //return all members in a job
        uriMatcher.addURI(JobMetaData.AUTHORITY, "*/members/",
                          ALL_MEMBERS_URI);
        //ADDITIONAL URI
        uriMatcher.addURI(JobMetaData.AUTHORITY, "*/reverse/*",
                          REVERSE_URI);

}

And the last Uri is not recognized using: uriMatcher.match(uri)

On the previous question (mentioned earlier) it was recommended that I move the offending Uri to the top of the calls to UriMatcher.put(String, int). That solved the previous problem (and left me with a bad taste in my mouth). Trying the same solution with this code results in the current first Uri (JOBNAME_SINGLE_URI) going unrecognized. I'm fairly sure that the issue isn't in my code (I've managed to create a working ContentProvider utilizing Uris and debug all of the problems with them prior to this issue), but rather is an issue with Uri matching in Android.

UPDATE:

public final static String AUTHORITY = "dsndata.sds2mobile.jobprovider";

Sample Uri:
content://dsndata.sds2mobile.jobprovider/SDS2MobileDemo/reverse/C_1

Answer 1

There are three rules that aren't well documented but that are crucial to understanding the matching mechanism of UriMatcher:

1. UriMatcher tries to match the entire Uri against the pattern. Much like the matches() method of java.util.regex.Matcher that returns true only if the entire region sequence matches the matcher's pattern (compared to the find() method that returns true for partial matches).
2. Wildcards are applied to one path segment only, meaning * or SDS2MobileDemo/* will never match SDS2MobileDemo/reverse/C_1 but */*/* or */*/C_1 will.
3. Once it finds a match for a path segment it won't find any alternative match for that particular path segment.

Here are some examples using the following url: content://dsndata.sds2mobile.jobprovider/SDS2MobileDemo/reverse/C_1

The first two rules are easy to understand:

• SDS2MobileDemo/*/* will match
• */reverse/* will match
• */* won't match because it matches only two path segments
• SDS2MobileDemo won't match because it matches only one path segment

The third rule is a little harder to understand. If you add the following Uris in this exact order:

• */wrong/C_1
• SDS2MobileDemo/reverse/C_1

then it won't find a match because that translates into the following (pseudo) code:

if ("*".matches("SDS2MobileDemo")) {    
    // tries to match the other parts but fails    
}
else if ("SDS2MobileDemo".matches("SDS2MobileDemo")) {
    // will never be executed
}

If you reverse the order the (pseudo) code becomes:

if ("SDS2MobileDemo".matches("SDS2MobileDemo")) {    
    // tries to match the other parts and succeeds    
}    
else if ("*".matches("SDS2MobileDemo")) {    
    // will never be executed    
}

Now as far as the original question goes. SDS2MobileDemo/reverse/C_1 will get matched by */reverse/* but not e.g. JobNames/reverse/C_1 because that one will go down the JobNames/* path... Also it's clear that moving */reverse/* to the top isn't the solution because all other patterns not starting with * won't match any more. There's really no telling what the correct solution is as long as it's unknown which patterns should match which Uris.