How to configure encoding in Maven?

Question

When I run maven install on my multi module maven project I always get the following output:

[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!

So, I googled around a bit, but all I can find is that I have to add:

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>

...to my pom.xml. But it's already there (in the parent pom.xml).

Configuring <encoding> for the maven-resources-plugin or the maven-compiler-plugin also doesn't fix it.

So what's the problem?

Solution 1

OK, I have found the problem.

I use some reporting plugins. In the documentation of the failsafe-maven-plugin I found, that the <encoding> configuration - of course - uses ${project.reporting.outputEncoding} by default.

So I added the property as a child element of the project element and everything is fine now:

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
</properties>

See also http://maven.apache.org/general.html#encoding-warning

Solution 2

This would be in addition to previous, if someone meets a problem with scandic letters that isn't solved with the solution above.

If the java source files contain scandic letters they need to be interpreted correctly by the Java used for compiling. (e.g. scandic letters used in constants)

Even that the files are stored in UTF-8 and the Maven is configured to use UTF-8, the System Java used by the Maven will still use the system default (eg. in Windows: cp1252).

This will be visible only running the tests via maven (possibly printing the values of these constants in tests. The printed scandic letters would show as '< ?>') If not tested properly, this would corrupt the class files as compile result and be left unnoticed.

To prevent this, you have to set the Java used for compiling to use UTF-8 encoding. It is not enough to have the encoding settings in the maven pom.xml, you need to set the environment variable: JAVA_TOOL_OPTIONS = -Dfile.encoding=UTF8

Also, if using Eclipse in Windows, you may need to set the encoding used in addition to this (if you run individual test via eclipse).

Solution 3

If you combine the answers above, finally a pom.xml that configured for UTF-8 should seem like that.

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>YOUR_COMPANY</groupId>
    <artifactId>YOUR_APP</artifactId>
    <version>1.0.0-SNAPSHOT</version>

    <properties>
        <project.java.version>1.8</project.java.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    </properties>

    <dependencies>
        <!-- Your dependencies -->
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.7.0</version>
                <configuration>
                    <source>${project.java.version}</source>
                    <target>${project.java.version}</target>
                    <encoding>${project.build.sourceEncoding}</encoding>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-resources-plugin</artifactId>
                <version>3.0.2</version>
                <configuration>
                    <encoding>${project.build.sourceEncoding}</encoding>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

Solution 4

It seems people mix a content encoding with a built files/resources encoding. Having only maven properties is not enough. Having -Dfile.encoding=UTF8 not effective. To avoid having issues with encoding you should follow the following simple rules

1. Set maven encoding, as described above:

<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>

2. Always set encoding explicitly, when work with files, strings, IO in your code. If you do not follow this rule, your application depend on the environment. The -Dfile.encoding=UTF8 exactly is responsible for run-time environment configuration, but we should not depend on it. If you have thousands of clients, it takes more effort to configure systems and to find issues because of it. You just have an additional dependency on it which you can avoid by setting it explicitly. Most methods in Java that use a default encoding are marked as deprecated because of it.

3. Make sure the content, you are working with, also is in the same encoding, that you expect. If it is not, the previous steps do not matter! For instance a file will not be processed correctly, if its encoding is not UTF8 but you expect it. To check file encoding on Linux:

$ file --mime F_PRDAUFT.dsv

4. Force clients/server set encoding explicitly in requests/responses, here are examples:

@Produces("application/json; charset=UTF-8")
@Consumes("application/json; charset=UTF-8")

Hope this will be useful to someone.

Solution 5

Try this:

<project>
  ...
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-resources-plugin</artifactId>
        <version>2.7</version>
        <configuration>
          ...
          <encoding>UTF-8</encoding>
          ...
        </configuration>
      </plugin>
    </plugins>
    ...
  </build>
  ...
</project>

View more solutions