## Using the batch compiler

### Finding the batch compiler

The batch compiler class is located in the JDT Core plug-in. The name of the class is org.eclipse.jdt.compiler.batch.BatchCompiler. It is packaged into `plugins/org.eclipse.jdt.core_<version>.jar`. Since 3.2, it is also available as a separate download. The name of the file is `ecj.jar`. Its corresponding source is also available. To get them, go to the download page and search for the section JDT Core Batch Compiler. This jar contains the batch compiler and the javac ant adapter.

Since 3.3, this jar also contains the support for jsr199 (Compiler API) and the support for jsr269 (Annotation processing). In order to use the annotations processing support, a 1.6 VM is required.

So it can be used as a standalone application and inside an Ant build outside of Eclipse.

### Running the batch compiler

- From the command line.

  `java -jar org.eclipse.jdt.core_<version>.jar -classpath rt.jar A.java`

  or:

  `java -jar ecj.jar -classpath rt.jar A.java`

- Using the static `compile(String commandLine, PrintWriter outWriter, PrintWriter errWriter, CompilationProgress progress)` method of the class BatchCompiler.

      org.eclipse.jdt.compiler.CompilationProgress progress = null; // instantiate your subclass
      org.eclipse.jdt.internal.compiler.batch.BatchCompiler.compile(
         "-classpath rt.jar A.java",
         new PrintWriter(System.out),
         new PrintWriter(System.err),
         progress);

  You can control how progress is reported, or how the batch compiler is canceled, by subclassing the class org.eclipse.jdt.compiler.CompilationProgress.

#### Which options are available?

The recommended options have an orange background.

When some options are being set multiple times, the batch compiler consumes them from left to right. When the warning option (-warn:....) is used without '+' or '-', this overrides the set of warnings previously specified. So the user should make sure that such an option is given before any other usage of the -warn option.

Same applies for the -err: option.

Name | Usage
--- | ---
Classpath options

-bootclasspath <dir 1>;<dir 2>;...;<dir P>

This is a list of directories or jar files used to bootstrap the class files used by the compiler. By default the libraries of the running VM are used. Entries are separated by the platform path separator.
Each directory or file can specify access rules for types between '[' and ']'.

If no bootclasspath is specified, the compiler will infer it using the following system properties `sun.boot.class.path`, `vm.boot.class.path` or `org.apache.harmony.boot.class.path` in this order respectively.

-cp
-classpath <dir 1>;<dir 2>;...;<dir P>

This is a list of directories or jar files used to compile the source files. The default value is the value of the property "java.class.path". Entries are separated by the platform path separator.
Each directory or file can specify access rules for types between '[' and ']' (e.g. [-X] to forbid access to type X, [~X] to discourage access to type X, [+p/X:-p/*] to forbid access to all types in package p but allow access to p/X).
The compiler follows the `Class-Path` clauses of jar files' manifests recursively and appends each referenced jar file to the end of the classpath, provided it is not on the classpath yet.

-extdirs <dir 1>;<dir 2>;...;<dir P> | This is a list of directories used to specify the location of extension zip/jar files. Entries are separated by the platform path separator.
-endorseddirs <dir 1>;<dir 2>;...;<dir P> | This is a list of directories used to specify the location of endorsed zip/jar files. Entries are separated by the platform path separator.
-sourcepath <dir 1>;<dir 2>;...;<dir P> | This is a list of directories used to specify the source files. Entries are separated by the platform path separator. Each directory can specify access rules for types between '[' and ']'.
-d <dir 1>|none | This is used to specify in which directory the generated .class files should be dumped. If it is omitted, no package directory structure is created. If you want to generate no .class file at all, use -d none.

-encoding <encoding name>

Specify default encoding for all source files. Custom encoding can also be specified on a per file basis by suffixing each input source file/folder name with [<encoding name>]. For example X.java[utf8] would specify the `UTF-8` encoding for the compilation unit X.java located in the current user directory.

If multiple default source file encodings are specified, the last one will be used.

For example:

- `... -encoding UTF-8 X.java[Cp1252] Y.java[UTF-16] Z.java ....`
  All source files will be read using UTF-8 encoding (this includes Z.java). X.java will be read using Cp1252 encoding and Y.java will be read using UTF-16 encoding.
- `... -encoding UTF-8 -encoding UTF-16 ....`
  All source files will be read using UTF-16 encoding. The -encoding option for UTF-8 is ignored.
- `... -encoding Cp1252 /foo/bar/X.java[UTF-16] /foo/bar[UTF-8] ....`
  All source files will be read using Cp1252 encoding. X.java is the only file inside the /foo/bar directory to be read using the encoding UTF-16. All other files in that directory will use UTF-8 encoding.

Compliance options

-target 1.1 to 1.7 or (5, 5.0, etc)

This specifies the .class file target setting. The possible value are:

- 1.1 (major version: 45 minor: 3)
- 1.2 (major version: 46 minor: 0)
- 1.3 (major version: 47 minor: 0)
- 1.4 (major version: 48 minor: 0)
- 1.5, 5 or 5.0 (major version: 49 minor: 0)
- 1.6, 6 or 6.0 (major version: 50 minor: 0)
- 1.7, 7 or 7.0 (major version: 51 minor: 0)

Defaults are:

- 1.1 in -1.3 mode
- 1.2 in -1.4 mode
- 1.5 in -1.5 mode
- 1.6 in -1.6 mode
- 1.7 in -1.7 mode

clcd1.1 can be used to generate the StackMap attribute.

-1.3 | Set compliance level to 1.3. Implicit -source 1.3 -target 1.1.
-1.4 | Set compliance level to 1.4 (default). Implicit -source 1.3 -target 1.2.
-1.5 | Set compliance level to 1.5. Implicit -source 1.5 -target 1.5.
-1.6 | Set compliance level to 1.6. Implicit -source 1.6 -target 1.6.
-1.7 | Set compliance level to 1.7. Implicit -source 1.7 -target 1.7.

-source 1.1 to 1.7 or (5, 5.0, etc)

This is used to specify the source level expected by the compiler.
The possible value are:

- 1.3
- 1.4
- 1.5, 5 or 5.0
- 1.6, 6 or 6.0
- 1.7, 7 or 7.0

Defaults are:

- 1.3 in -1.3 mode
- 1.3 in -1.4 mode
- 1.5 in -1.5 mode
- 1.6 in -1.6 mode
- 1.7 in -1.7 mode

In 1.4, assert is treated as a keyword. In 1.5 and 1.6, enum and assert are treated as a keywords.

Warning options
-?:warn -help:warn | Display advanced warning options

-warn:...

Specify the set of enabled warnings.
e.g. -warn:unusedLocal,deprecation

-warn:none | disable all warnings
-warn:<warning tokens separated by ,> | enable exactly the listed warnings
-warn:+<warning tokens separated by ,> | enable additional warnings
-warn:-<warning tokens separated by ,> | disable specific warnings

In the column Default below, a mark "+/-" indicates that an option covers several fine grained warning variants, some of which are enabled by default, others disabled. This means that specifying the given option with "+" will enable more warnings than the default, and specifying "-" disables some that are enabled by default.

Default | Token name | Description
+/- | allDeadCode | dead code including trivial if (DEBUG) check
+/- | allDeprecation | deprecation even inside deprecated code
- | allJavadoc | invalid or missing javadoc
- | allOver-ann | all missing @Override annotations (superclass and superinterfaces)
- | all-static-method | all method can be declared as static warnings
+ | assertIdentifier | occurrence of assert used as identifier
- | boxing | autoboxing conversion
+ | charConcat | when a char array is used in a string concatenation without being converted explicitly to a string
+ | compareIdentical | comparing identical expressions
- | conditionAssign | possible accidental boolean assignment
+ | constructorName | method with constructor name
+ | deadCode | dead code excluding trivial if (DEBUG) check
- | dep-ann | missing @Deprecated annotation
+/- | deprecation | usage of deprecated type or member outside deprecated code
+ | discouraged | use of types matching a discouraged access rule
- | emptyBlock | undocumented empty block
+ | enumIdentifier | occurrence of enum used as identifier
- | enumSwitch | incomplete enum switch
- | fallthrough | possible fall-through case
- | fieldHiding | field hiding another variable
+ | finalBound | type parameter with final bound
+ | finally | finally block not completing normally
+ | forbidden | use of types matching a forbidden access rule
- | hashCode | missing hashCode() method when overriding equals()
+/- | hiding | macro for fieldHiding, localHiding, typeHiding and maskedCatchBlock
- | includeAssertNull | raise null warnings for variables that got tainted in an assert expression
- | indirectStatic | indirect reference to static member
+ | intfAnnotation | annotation type used as super interface
+ | intfNonInherited | interface non-inherited method compatibility
- | intfRedundant | find redundant superinterfaces
- | javadoc | invalid javadoc
- | localHiding | local variable hiding another variable
+ | maskedCatchBlock | hidden catch block
- | nls | non-nls string literals (lacking of tags //$NON-NLS-<n>)
+ | noEffectAssign | assignment with no effect
+/- | null | potential missing or redundant null check
- | nullAnnot | enable annotation based null analysis. If desired, the annotation types to be interpreted by the compiler can be specified by appending (nullable|nonnull|nonnullbydefault), where each annotation type is specified using its fully qualified name. See also -nonNullByDefault below.
- | nullDereference | missing null check
- | over-ann | missing @Override annotation (superclass only)
- | paramAssign | assignment to a parameter
+ | pkgDefaultMethod | attempt to override package-default method
+ | raw | usage a of raw type (instead of a parameterized type)
+/- | resource | (potentially) unsafe usage of resource of type Closeable
- | semicolon | unnecessary semicolon or empty statement
+ | serial | missing serialVersionUID
- | specialParamHiding | constructor or setter parameter hiding another field
+/- | static-access | macro for indirectStatic and staticReceiver
- | static-method | an instance method that could be as a static method
+ | staticReceiver | if a non static receiver is used to get a static field or call a static method
- | super | overriding a method without making a super invocation
+ | suppress | enable @SuppressWarnings
- | syncOverride | missing synchronized in synchronized method override
- | syntheticAccess | when performing synthetic access for innerclass
- | tasks | enable support for tasks tags in source code
+ | typeHiding | type parameter hiding another type
+ | unavoidableGenericProblems | ignore unavoidable type safety problems due to raw APIs
+ | unchecked | unchecked type operation
- | unnecessaryElse | unnecessary else clause
- | unqualifiedField | unqualified reference to field
+/- | unused | macro for unusedAllocation, unusedArgument, unusedImport, unusedLabel, unusedLocal, unusedPrivate, unusedThrown and unusedTypeArgs
- | unusedAllocation | allocating an object that is not used
- | unusedArgument | unused method argument
+ | unusedImport | unused import reference
+ | unusedLabel | unused label
+ | unusedLocal | unused local variable
+ | unusedPrivate | unused private member declaration
- | unusedThrown | unused declared thrown exception
+ | unusedTypeArgs | unused type arguments for method and constructor
- | uselessTypeCheck | unnecessary cast/instanceof operation
+ | varargsCast | varargs argument need explicit cast
+/- | warningToken | unhandled or unused warning token in @SuppressWarnings
-nowarn | No warning (equivalent to -warn:none)

-err:...

Specify the set of enabled warnings that are converted to errors.
e.g. -err:unusedLocal,deprecation
unusedLocal and deprecation warnings will be converted to errors. All other warnings are still reported as warnings.

-err:<warning tokens separated by ,> | convert exactly the listed warnings to errors
-err:+<warning tokens separated by ,> | convert additional warnings to errors
-err:-<warning tokens separated by ,> | remove specific warnings from being converted to errors

-deprecation | Equivalent to -warn:+deprecation.

-properties <file>

Set warnings/errors option based on the properties file contents. This option can be used with -nowarn, -err:.. or -warn:.. options, but the last one on the command line sets the options to be used.

The properties file contents can be generated by setting project specific settings on an existing java project and using the file in `.settings/org.eclipse.jdt.core.prefs` file as a properties file, or a simple text file that is defined entry/value pairs using the constants defined in the `org.eclipse.jdt.core.JavaCore` class.

    ...
    org.eclipse.jdt.core.compiler.problem.annotationSuperInterface=warning
    org.eclipse.jdt.core.compiler.problem.assertIdentifier=warning
    org.eclipse.jdt.core.compiler.problem.autoboxing=ignore
    ...

Debug options

-g[:none|:lines,vars,source]

Set the debug attributes level

-g | All debug info (equivalent to -g:lines,vars,source)
-g:none | No debug info
-g:[lines,vars,source] | Selective debug info

-preserveAllLocals | Explicitly request the compiler to preserve all local variables (for debug purpose). If omitted, the compiler will remove unused locals.
Annotation processing options (require a 1.6 VM or above and are used only if the compliance is 1.6)
-Akey[=value] | Annotation processors options that are passed to annotation processors. `key` is made of identifiers separated by dots

-proc:[only|none]

If `-proc:only` is specified, the annotation processors will run but no compilation will be performed. If `-proc:none` is specified, annotation processors will not be discovered or run; compilation will proceed as if no annotation processors were found. By default the compiler must search the classpath for annotation processors, so specifying `-proc:none` may speed compilation if annotation processing is not required.

-processor <class1[,class2,...]> | Qualified class names of annotation processors to run. If specified, the normal processor discovery process will be skipped.
-processorpath <dir 1>;<dir 2>;...;<dir P> | A list of directories or jar files which will be searched for annotation processors. Entries are separated by the platform path separator. If not specified, the classpath will be searched instead.
-s <dir> | The directory where generated source files will be created.
-XprintProcessorInfo | Print information about which annotations and which elements a processor is asked to process
-XprintRounds | Print information about annotation processing rounds
-classNames <class1[,class2,...]> | Qualified names of binary types that need to be processed
Ignored options (for compatibility with javac options)
-J<option> | Pass option to the virtual machine
-X<option> | Specify non-standard option. -Xemacs is not ignored.
-X | Print non-standard options and exit
-O | Optimize for execution time
Advanced options
@<file> | Read command-line arguments from file
-maxProblems <n> | Max number of problems per compilation unit (100 by default)
-log <filename> | Specify a log file in which all output from the compiler will be dumped. This is really useful if you want to debug the batch compiler or get a file which contains all errors and warnings from a batch build. If the extension is .xml, the generated log will be an xml file.
-Xemacs | Use emacs style to present errors and warnings locations into the console and regular text logs. XML logs are unaffected by this option. With this option active, the message: `2. WARNING in /workspace/X.java (at line 8)...` is presented as: `/workspace/X.java:8: warning: The method...`

-proceedOnError[:Fatal]

Keep compiling in spite of errors, dumping class files with problem methods or problem types. This is recommended only if you want to be able to run your application even if you have remaining errors.
With ":Fatal", all optional errors are treated as fatal and this leads to code that will abort if an error is reached at runtime. Without ":Fatal", optional errors don't prevent the proper code generation and the produced .class files can be run without a problem.

-verbose | Print accessed/processed compilation units in the console or the log file if specified.
-referenceInfo | Compute reference info. This is useful only if connected to the builder. The reference infos are useless otherwise.
-progress | Show progress (only in -log mode).
-time | Display speed information.
-noExit | Do not call System.exit(n) at end of compilation (n=0 if no error).
-repeat <n> | Repeat compilation process <n> times (perf analysis).
-inlineJSR | Inline JSR bytecode (implicit if target >= 1.5).
-enableJavadoc | Consider references inside javadoc.
-missingNullDefault | When annotation based null analysis is enabled (using "nullAnnot", above), this option will raise a warning whenever there is no default annotation on a package or a type.
Helping options
-? -help | Display the help message.
-v -version | Display the build number of the compiler. This is very useful to report a bug.
-showversion | Display the build number of the compiler and continue. This is very useful to report a bug.

#### Examples

`d:\temp -classpath rt.jar -time -g -d d:/tmp` | It compiles all source files in d:\temp and its subfolders. The classpath is simply rt.jar. It generates all debug attributes and all generated .class files are dumped in d:\tmp. The speed of the compiler will be displayed once the batch process is completed.
`d:\temp\Test.java -classpath d:\temp;rt.jar -g:none` | It compiles only Test.java and its dependant files if any, retrieving dependant files from d:\temp. The classpath is d:\temp followed by rt.jar, which means that all necessary classes are searched first in d:\temp and then in rt.jar. It generates no debug attributes and all generated .class files are dumped in d:\temp.