java-quality

What this skill does

# Java Quality - Quick Reference

## When NOT to Use This Skill
- **SonarQube generic setup** - Use `sonarqube` skill
- **Spring Boot testing** - Use Spring Boot test skills
- **Security scanning** - Use `java-security` skill
- **Coverage reporting** - Use `jacoco` skill

> **Deep Knowledge**: Use `mcp__documentation__fetch_docs` with technology: `spring-boot` for framework-specific patterns.

## Tool Overview

| Tool | Focus | Speed | Integration |
|------|-------|-------|-------------|
| **Checkstyle** | Code style, formatting | Fast | Maven/Gradle |
| **SpotBugs** | Bug patterns, bytecode | Medium | Maven/Gradle |
| **PMD** | Code smells, complexity | Fast | Maven/Gradle |
| **SonarJava** | All-in-one | Slow | SonarQube |
| **Error Prone** | Compile-time bugs | Fast | Compiler plugin |

## Checkstyle Setup

### Maven Configuration

```xml
<!-- pom.xml -->
<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-checkstyle-plugin</artifactId>
    <version>3.3.1</version>
    <configuration>
        <configLocation>checkstyle.xml</configLocation>
        <consoleOutput>true</consoleOutput>
        <failsOnError>true</failsOnError>
        <violationSeverity>warning</violationSeverity>
    </configuration>
    <executions>
        <execution>
            <id>validate</id>
            <phase>validate</phase>
            <goals>
                <goal>check</goal>
            </goals>
        </execution>
    </executions>
    <dependencies>
        <dependency>
            <groupId>com.puppycrawl.tools</groupId>
            <artifactId>checkstyle</artifactId>
            <version>10.12.5</version>
        </dependency>
    </dependencies>
</plugin>
```

### checkstyle.xml (Google Style Based)

```xml
<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
    "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
    "https://checkstyle.org/dtds/configuration_1_3.dtd">

<module name="Checker">
    <property name="severity" value="warning"/>
    <property name="fileExtensions" value="java"/>

    <module name="TreeWalker">
        <!-- Naming -->
        <module name="ConstantName"/>
        <module name="LocalVariableName"/>
        <module name="MemberName"/>
        <module name="MethodName"/>
        <module name="PackageName"/>
        <module name="ParameterName"/>
        <module name="TypeName"/>

        <!-- Imports -->
        <module name="IllegalImport"/>
        <module name="RedundantImport"/>
        <module name="UnusedImports"/>

        <!-- Size -->
        <module name="LineLength">
            <property name="max" value="120"/>
        </module>
        <module name="MethodLength">
            <property name="max" value="50"/>
        </module>
        <module name="ParameterNumber">
            <property name="max" value="5"/>
        </module>

        <!-- Complexity -->
        <module name="CyclomaticComplexity">
            <property name="max" value="10"/>
        </module>
        <module name="NPathComplexity">
            <property name="max" value="200"/>
        </module>

        <!-- Best Practices -->
        <module name="EmptyBlock"/>
        <module name="EqualsHashCode"/>
        <module name="HiddenField"/>
        <module name="MissingSwitchDefault"/>
        <module name="SimplifyBooleanExpression"/>
        <module name="SimplifyBooleanReturn"/>
    </module>

    <!-- File-level checks -->
    <module name="FileLength">
        <property name="max" value="500"/>
    </module>
    <module name="NewlineAtEndOfFile"/>
</module>
```

### Commands

```bash
# Run Checkstyle
./mvnw checkstyle:check

# Generate report
./mvnw checkstyle:checkstyle
```

## SpotBugs Setup

### Maven Configuration

```xml
<!-- pom.xml -->
<plugin>
    <groupId>com.github.spotbugs</groupId>
    <artifactId>spotbugs-maven-plugin</artifactId>
    <version>4.8.3.0</version>
    <configuration>
        <effort>Max</effort>
        <threshold>Medium</threshold>
        <failOnError>true</failOnError>
        <plugins>
            <plugin>
                <groupId>com.h3xstream.findsecbugs</groupId>
                <artifactId>findsecbugs-plugin</artifactId>
                <version>1.12.0</version>
            </plugin>
        </plugins>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>check</goal>
            </goals>
        </execution>
    </executions>
</plugin>
```

### Exclude False Positives

```xml
<!-- spotbugs-exclude.xml -->
<?xml version="1.0" encoding="UTF-8"?>
<FindBugsFilter>
    <!-- Exclude generated code -->
    <Match>
        <Package name="~.*\.generated\..*"/>
    </Match>

    <!-- Exclude specific patterns -->
    <Match>
        <Bug pattern="EI_EXPOSE_REP"/>
        <Class name="~.*Dto"/>
    </Match>
</FindBugsFilter>
```

### Commands

```bash
# Run SpotBugs
./mvnw spotbugs:check

# Generate report
./mvnw spotbugs:spotbugs

# GUI viewer
./mvnw spotbugs:gui
```

### Common SpotBugs Warnings

| Bug ID | Description | Fix |
|--------|-------------|-----|
| NP_NULL_ON_SOME_PATH | Possible null dereference | Add null check or use Optional |
| EI_EXPOSE_REP | Returns mutable object | Return defensive copy |
| MS_SHOULD_BE_FINAL | Static field should be final | Add final modifier |
| SQL_INJECTION | SQL injection risk | Use parameterized queries |
| DM_DEFAULT_ENCODING | Uses default encoding | Specify charset explicitly |

## PMD Setup

### Maven Configuration

```xml
<!-- pom.xml -->
<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-pmd-plugin</artifactId>
    <version>3.21.2</version>
    <configuration>
        <rulesets>
            <ruleset>pmd-rules.xml</ruleset>
        </rulesets>
        <failOnViolation>true</failOnViolation>
        <printFailingErrors>true</printFailingErrors>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>check</goal>
            </goals>
        </execution>
    </executions>
</plugin>
```

### pmd-rules.xml

```xml
<?xml version="1.0"?>
<ruleset name="Custom Rules">
    <description>Custom PMD ruleset</description>

    <!-- Best Practices -->
    <rule ref="category/java/bestpractices.xml">
        <exclude name="JUnitTestContainsTooManyAsserts"/>
    </rule>

    <!-- Code Style -->
    <rule ref="category/java/codestyle.xml">
        <exclude name="AtLeastOneConstructor"/>
        <exclude name="OnlyOneReturn"/>
    </rule>

    <!-- Design -->
    <rule ref="category/java/design.xml">
        <exclude name="LawOfDemeter"/>
    </rule>

    <!-- Error Prone -->
    <rule ref="category/java/errorprone.xml"/>

    <!-- Performance -->
    <rule ref="category/java/performance.xml"/>

    <!-- Custom thresholds -->
    <rule ref="category/java/design.xml/CyclomaticComplexity">
        <properties>
            <property name="methodReportLevel" value="10"/>
        </properties>
    </rule>

    <rule ref="category/java/design.xml/CognitiveComplexity">
        <properties>
            <property name="reportLevel" value="15"/>
        </properties>
    </rule>
</ruleset>
```

### Commands

```bash
# Run PMD
./mvnw pmd:check

# Generate report
./mvnw pmd:pmd

# Copy-paste detection
./mvnw pmd:cpd
```

## Error Prone Setup

### Maven Configuration

```xml
<!-- pom.xml -->
<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.12.1</version>
    <configuration>
        <compilerArgs>
            <arg>-XDcompilePolicy=simple</arg>
            <arg>-Xplugin:ErrorProne</arg>
        </compilerArgs>
        <annotationProcessorPaths>
            <path>
                <groupId>com.google.errorprone</groupId>
                <artifactId>error_prone_core</artifactId>
                <version>2.24.1</version>
            </path>
        </annotationProcessorPaths>
    </configuration>
</plugin>
```

## Combined Quality Profile

### All-in-One Maven Profile

```xml
<!-- pom.xml -->
<profiles