java.lang.reflect.InvocationTargetException
Bad writing
The cause of the bug:
in the service layer, the value passed in by the public list findbyproperty (string propertyname, object value) {} method service of Dao layer is a value of string type, so an error is reported;
Modification:
rewrite the object type of Dao layer to string type to fix the bug.
[problem description]
User root is created in the/root/exercise folder HelloWorld.java The code is as follows:
Compile and run the file as follows:
Compile HelloWorld.java Generate bytecode file HelloWorld.class , running HelloWorld.class Error: could not find or load main class.
[cause analysis]
The current directory is the directory where the. Class file is located. To run the. Class bytecode file, you need to add the current directory to the system variable classpath to find the Java class in the current directory.
[solution]
Step 1: add the classpath system variable at the end of the profile file in/etc.:,. To represent the current path.
The classpath in the original/etc/profile file is:
CLASSPATH=$JAVA_ HOME/jre/lib/ext:$JAVA_ HOME/lib/ dt.jar :$JAVA_ HOME/lib/ tools.jar .
The added classpath is: classpath =.: $Java_ HOME/jre/lib/ext:$JAVA_ HOME/lib/ dt.jar :$JAVA_ HOME/lib/ tools.jar
Step 2: input source/etc/profile on the command line to make the system variables in/etc/profile effective and then run.
Note: you can modify system variables only if the current user is root. If you enter source/etc/profile on the command line, the system variable will only take effect temporarily. If you close terminal, the system variable will be restored to its original state. Because the system variable is loaded at system startup, the system variable will be loaded automatically only at the next system restart, so you don’t need to enter source/etc/profile again.
The results are as follows
This article is reproduced from:
Solution to the problem of index downloads are disabled, search result may be incomplete when Maven imports dependent jar packages
Maven adds the solution of dependency query with no result
to solve the problem
[problem description]
When importing dependent jar packages with maven, an error is reported: index downloads are disabled, search result may be incomplete
Sometimes, even if the error is not reported, the query still does not respond.
[solution]
1. Select Maven in preferences and select “download repository index updates on startup”.
2. Open the Maven warehouse.
3. Right click on the global warehouse and select “full index enabled”.
4. After selecting, Maven will download an index file of nearly 100 megabytes. After downloading, it will update the index. The process is relatively long, and it may get stuck. It is recommended not to do anything else during this period.
5. After that, we can search the content in select dependency.
Problem description:
j2ee web debugging process I found that no matter how I modified it did not change, and then I clean it, but after this program can not run, 404 can not find resources.
Reason analysis:
checked the path of the release project
controller in classes these folders are all directories, no files, after searching baidu, it should be a reference project lack of jar package, leading to the project build failure, but the empty directory was built, leading to this problem.
Solutions:
once I know what the problem is, I remove the jar from the path and add it again, and the project runs. 