author | Oleksandr Gavenko <gavenkoa@gmail.com> |
Mon, 19 Oct 2015 17:04:52 +0300 | |
changeset 1769 | cadd23f8127f |
parent 1687 | da4a6ceb7e89 |
child 1833 | 378b566fd86b |
permissions | -rw-r--r-- |
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.. -*- coding: utf-8; -*- |
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Include common header with quick links.
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.. include:: HEADER.rst |
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================ |
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Java language. |
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================ |
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.. contents:: |
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Class version. |
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============== |
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========= ====== ===================== |
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major minor Java platform version |
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========= ====== ===================== |
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45 0x27 3 1.0 |
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45 0x27 3 1.1 |
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46 0x28 0 1.2 |
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47 0x29 0 1.3 |
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48 0x30 0 1.4 |
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49 0x31 0 5.0 |
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50 0x32 0 6.0 |
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51 0x33 0 7 |
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52 0x34 0 8 |
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========= ====== ===================== |
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where ``minor`` and ``major`` are value of 6 and 8 bytes in .class file:: |
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0xCA, 0xFE, 0xBA, 0xBE, 0x00, minor, 0x00, major |
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Access modifiers. |
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================= |
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Public. |
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------- |
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* Public class is visible in other packages. |
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* Public field is visible everywhere (class must be public too). |
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Private. |
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-------- |
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* Private variables or methods may be used only by an instance of the same |
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class that declares the variable or method |
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* A private feature may only be accessed by the class that owns the feature. |
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Protected. |
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---------- |
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* Is available to all classes in the same package and also available to all |
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subclasses of the class that owns the protected feature. |
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* This access is provided even to subclasses that reside in a different |
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package from the class that owns the protected feature. |
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default. |
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-------- |
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What you get by default ie, without any access modifier. |
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* It means that it is visible to all within a particular package. |
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static. |
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------- |
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* Static means one per class, not one for each object no matter how many |
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instance of a class might exist. This means that you can use them without |
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creating an instance of a class. |
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* Static methods are implicitly final, because overriding is done based on |
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the type of the object, and static methods are attached to a class, not an |
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object. |
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* A static method in a superclass can be shadowed by another static method in |
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a subclass, as long as the original method was not declared final. |
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* You can't override a static method with a nonstatic method. |
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final. |
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------ |
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* A final class can't be extended ie., final class may not be subclassed. |
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* A final method can't be overridden when its class is inherited. |
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* You can't change value of a final variable. |
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Exceptions. |
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=========== |
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A checked exception is some subclass of Exception (or Exception itself), |
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excluding class RuntimeException and its subclasses. |
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Unchecked exceptions are RuntimeException and any of its subclasses. Class |
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Error and its subclasses also are unchecked. With an unchecked exception, |
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however, the compiler doesn't force client programmers either to catch the |
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exception or declare it in a throws clause. |
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Inner classes. |
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============== |
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Nested top-level classes. |
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------------------------- |
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If you declare a class within a class and specify the static modifier, the |
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compiler treats the class just like any other top-level class. |
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Any class outside the declaring class accesses the nested class with the |
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declaring class name acting similarly to a package. eg, outer.inner. Top-level |
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inner classes implicitly have access only to static variables. There can also |
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be inner interfaces. All of these are of the nested top-level variety. |
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Member classes. |
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--------------- |
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Member inner classes are just like other member methods and member variables |
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and access to the member class is restricted, just like methods and variables. |
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This means a public member class acts similarly to a nested top-level class. |
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The primary difference between member classes and nested top-level classes is |
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that member classes have access to the specific instance of the enclosing |
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class. |
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Local classes. |
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-------------- |
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Local classes are like local variables, specific to a block of code. Their |
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visibility is only within the block of their declaration. In order for the |
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class to be useful beyond the declaration block, it would need to implement a |
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more publicly available interface. |
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Because local classes are not members, the modifiers public, protected, |
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private, and static are not usable. |
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Anonymous classes. |
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------------------ |
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Anonymous inner classes extend local inner classes one level further. As |
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anonymous classes have no name, you cannot provide a constructor. |
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64-bit problem. |
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=============== |
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http://www.java.com/en/download/faq/java_win64bit.xml |
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Which version of Java should I download for my 64-bit Windows |
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operating system? |
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http://java.sun.com/javase/6/webnotes/install/system-configurations.html |
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Java SE 6 Release Notes Supported System Configurations |
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Java performance. |
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================= |
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http://java.sun.com/performance/reference/whitepapers/5.0_performance.html |
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http://java.sun.com/performance/reference/whitepapers/6_performance.html |
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Creating jar. |
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============= |
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:: |
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$ jar cf myFile.jar *.class |
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$ jar cmf myManifestFile myFile.jar *.class |
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$ jar -cfe Main.jar foo.Main foo/Main.class |
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Profiling Java. |
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=============== |
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:: |
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$ java -Xprof com.vendor.product.Clazz |
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java -Xrunhprof:help
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$ java -Xrunhprof:help |
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Debugging Java. |
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=============== |
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Compile with ``-g`` to preserve source code information:: |
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$ javac -g -cp $CLASSPATH -sourcepath $SRC_DIR -d $BUILD_DIR |
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To run Java program in debugger:: |
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$ jdb -cp $CLASSPATH -sourcepath $SRC_DIR |
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-Xrunjdwp:transport
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To attach to Java application you firstly must run application with (use |
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-Xrunjdwp:transport
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``dt_shmem`` for Windows and ``dt_socket`` for Linux):: |
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$ java -Xdebug -Xrunjdwp:transport=dt_shmem,server=y,suspend=n,address=$PORT \ |
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com.vendor.product.Clazz |
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and then attach with debugger:: |
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$ jdb -attach $PORT |
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Dump current thread traces.
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Dump current thread traces and memory statistic to stdout:: |
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Dump current thread traces.
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Dump current thread traces.
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$ kill -QUIT $PID |
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Dump current thread traces.
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Debug class loading.
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Debug class loading. |
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Debug class loading.
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==================== |
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Debug class loading.
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Debug class loading.
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To dump class loading and unloading to ``System.out`` add to ``java`` opts:: |
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Debug class loading.
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Debug class loading.
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$ java -XX:+TraceClassLoading -XX:+TraceClassUnloading ... |
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$ java -verbose:class ... |
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Debug class loading.
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Debug class loading.
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To review loaded classes explore heap dump in ``visualvm`` (visit "Classes" |
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Debug class loading.
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tab). |
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Debug class loading.
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Decompile class file.
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Decompile class file. |
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Decompile class file.
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===================== |
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Decompile class file.
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:: |
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Decompile class file.
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Decompile class file.
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$ javap -v -p -c My.java |
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Decompile class file.
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Find jar by class. |
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================== |
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http://mvnrepository.com/search.html?query=PKG
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http://mvnrepository.com/search.html?query=PKG |
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http://www.jarfinder.com |
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Set default Java in Debian.
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Set default Java in Debian. |
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Set default Java in Debian.
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=========================== |
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Set default Java in Debian.
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:: |
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Set default Java in Debian.
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|
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Set default Java in Debian.
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$ update-java-alternatives -l |
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Set default Java in Debian.
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$ sudo update-java-alternatives -s java-1.8.0-openjdk-i386 |
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Set default Java in Debian.
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|
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Set default Java in Debian.
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or individually for each executable:: |
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Set default Java in Debian.
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|
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Set default Java in Debian.
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$ sudo update-alternatives --config java |
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Set default Java in Debian.
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Import SSL certificate.
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Import SSL certificate. |
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Import SSL certificate.
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======================= |
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Import SSL certificate.
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|
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Import SSL certificate.
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Get cert with:: |
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Import SSL certificate.
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|
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Import SSL certificate.
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$ openssl s_client -connect promin-test.it.loc:433 |
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Import SSL certificate.
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|
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Import SSL certificate.
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-----BEGIN CERTIFICATE----- |
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Import SSL certificate.
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... |
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Import SSL certificate.
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-----END CERTIFICATE----- |
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Import SSL certificate.
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|
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Import SSL certificate.
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or by opening URL in broswer and exporting in "Page info" ==> "Security" menu. |
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Import SSL certificate.
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|
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Import SSL certificate.
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Call import utility with default ``changeit`` password:: |
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Import SSL certificate.
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|
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Import SSL certificate.
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$ keytool -importcert -file $YOUR.crt -keystore $JAVA_HOME/jre/lib/security/cacert -alias $ANY -storepass changeit |
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Import SSL certificate.
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$ keytool -list -v -keystore $JAVA_HOME/jre/lib/security/cacert -storepass changeit |
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Import SSL certificate.
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|
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Import SSL certificate.
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Import certificate system wide in Debian by (note, ``.crt`` extention is |
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Import SSL certificate.
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mandatory):: |
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Import SSL certificate.
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|
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Import SSL certificate.
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|
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$ sudo mkdir /usr/share/ca-certificates/$ANY/ # don't mess with other certs |
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Import SSL certificate.
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$ sudo cp /tmp/$YOUR.crt /usr/share/ca-certificates/$ANY/ |
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Import SSL certificate.
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parents:
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|
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$ sudo dpkg-reconfigure --force ca-certificates # check your cert in curses GUI! |
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Import SSL certificate.
Oleksandr Gavenko <gavenkoa@gmail.com>
parents:
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|
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$ sudo update-ca-certificates --fresh --verbose |
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Import SSL certificate.
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parents:
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|
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Java EE versions. |
250 |
================= |
|
251 |
||
252 |
======= ======== ======== ======== |
|
253 |
Java EE Servlet JSP JSTL |
|
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======= ======== ======== ======== |
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6 3.0 2.2 - |
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5 2.5 2.1 1.2 |
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1.4 2.4 2.0 1.1 |
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1.2 2.3 1.2 1.0 |
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======= ======== ======== ======== |
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||
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To set servlet version check ``WEB-INF/web.xml``:: |
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<web-app xmlns="http://java.sun.com/xml/ns/javaee" version="3.0"> |
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See: |
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http://jcp.org/aboutJava/communityprocess/final/jsr315/index.html |
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Servlet 3.0 Specification |
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http://jcp.org/aboutJava/communityprocess/mrel/jsr154/index.html |
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Servlet 2.5 Specification |
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http://www.mularien.com/blog/2008/04/24/how-to-reference-and-use-jstl-in-your-web-application/ |
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How to Reference and Use JSTL in your Web Application |
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http://en.wikipedia.org/wiki/Java_EE_version_history |
|
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Java EE version history |
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Java interactive shell.
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Java interactive shell.
Oleksandr Gavenko <gavenkoa@gmail.com>
parents:
1380
diff
changeset
|
276 |
Java interactive shell. |
9b4441d30cac
Java interactive shell.
Oleksandr Gavenko <gavenkoa@gmail.com>
parents:
1380
diff
changeset
|
277 |
======================= |
9b4441d30cac
Java interactive shell.
Oleksandr Gavenko <gavenkoa@gmail.com>
parents:
1380
diff
changeset
|
278 |
|
9b4441d30cac
Java interactive shell.
Oleksandr Gavenko <gavenkoa@gmail.com>
parents:
1380
diff
changeset
|
279 |
Just use Groovy. ``bsh`` is older alternative without code completion. |