java String转Date问题

string datestr="2015-15-12";

simpledateformat sdf = new simpledateformat("yyyy-mm-dd   ");  

date date = sdf.parse(datestr); 

java.text.parseexception: unparseable date: "2015-15-12"

at java.text.dateformat.parse(unknown source)

at cn.xh.mybatis.test.usermappertest.testinsertuser(usermappertest.java:75)

at sun.reflect.nativemethodaccessorimpl.invoke0(native method)

at sun.reflect.nativemethodaccessorimpl.invoke(unknown source)

at sun.reflect.delegatingmethodaccessorimpl.invoke(unknown source)

at java.lang.reflect.method.invoke(unknown source)

at org.junit.runners.model.frameworkmethod$1.runreflectivecall(frameworkmethod.java:50)

at org.junit.internal.runners.model.reflectivecallable.run(reflectivecallable.java:12)

at org.junit.runners.model.frameworkmethod.invokeexplosively(frameworkmethod.java:47)

at org.junit.internal.runners.statements.invokemethod.evaluate(invokemethod.java:17)

at org.junit.internal.runners.statements.runbefores.evaluate(runbefores.java:26)

at org.junit.runners.parentrunner.runleaf(parentrunner.java:325)

at org.junit.runners.blockjunit4classrunner.runchild(blockjunit4classrunner.java:78)

at org.junit.runners.blockjunit4classrunner.runchild(blockjunit4classrunner.java:57)

at org.junit.runners.parentrunner$3.run(parentrunner.java:290)

at org.junit.runners.parentrunner$1.schedule(parentrunner.java:71)

at org.junit.runners.parentrunner.runchildren(parentrunner.java:288)

at org.junit.runners.parentrunner.access$000(parentrunner.java:58)

at org.junit.runners.parentrunner$2.evaluate(parentrunner.java:268)

at org.junit.runners.parentrunner.run(parentrunner.java:363)

at org.eclipse.jdt.internal.junit4.runner.junit4testreference.run(junit4testreference.java:86)

at org.eclipse.jdt.internal.junit.runner.testexecution.run(testexecution.java:38)

at org.eclipse.jdt.internal.junit.runner.remotetestrunner.runtests(remotetestrunner.java:459)

at org.eclipse.jdt.internal.junit.runner.remotetestrunner.runtests(remotetestrunner.java:675)

at org.eclipse.jdt.internal.junit.runner.remotetestrunner.run(remotetestrunner.java:382)

at org.eclipse.jdt.internal.junit.runner.remotetestrunner.main(remotetestrunner.java:192)

是因为："yyyy-mm-dd   "多了一个空格。"2015-15-12"没有空格导致格式化出错，格式改一样就好了。