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# XML I/O Operations
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XML readers and writers for serializing models to and from POM files with location tracking and formatting preservation. These classes handle the conversion between Maven Model objects and XML POM files.
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## Capabilities
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### MavenXpp3Reader
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Standard XML reader for parsing POM files into Model objects using XPP3 parser.
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```java { .api }
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public class MavenXpp3Reader {
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    // Basic reading methods
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    public Model read(Reader reader) throws IOException, XmlPullParserException;
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    public Model read(InputStream in) throws IOException, XmlPullParserException;
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    public Model read(Reader reader, boolean strict) throws IOException, XmlPullParserException;
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    public Model read(InputStream in, boolean strict) throws IOException, XmlPullParserException;
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    // Advanced methods with encoding
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    public Model read(Reader reader, boolean strict, InputSource source) throws IOException, XmlPullParserException;
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    public Model read(InputStream in, boolean strict, String encoding, InputSource source) throws IOException, XmlPullParserException;
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}
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```
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**Usage Example:**
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```java
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import org.apache.maven.model.Model;
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import org.apache.maven.model.io.xpp3.MavenXpp3Reader;
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import java.io.FileReader;
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import java.io.IOException;
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import org.codehaus.plexus.util.xml.pull.XmlPullParserException;
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MavenXpp3Reader reader = new MavenXpp3Reader();
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try {
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    // Read from file
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    Model model = reader.read(new FileReader("pom.xml"));
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    // Read with strict parsing disabled (allows unknown elements)
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    Model model2 = reader.read(new FileReader("pom.xml"), false);
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    System.out.println("Project: " + model.getArtifactId());
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    System.out.println("Version: " + model.getVersion());
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} catch (IOException | XmlPullParserException e) {
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    System.err.println("Error reading POM: " + e.getMessage());
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}
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```
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### MavenXpp3ReaderEx
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Extended XML reader with location tracking support for error reporting and IDE integration.
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```java { .api }
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public class MavenXpp3ReaderEx {
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    // Reading methods with location tracking
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    public Model read(Reader reader) throws IOException, XmlPullParserException;
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    public Model read(InputStream in) throws IOException, XmlPullParserException;
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    public Model read(Reader reader, boolean strict) throws IOException, XmlPullParserException;
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    public Model read(InputStream in, boolean strict) throws IOException, XmlPullParserException;
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    // Advanced methods with encoding and source tracking
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    public Model read(Reader reader, boolean strict, InputSource source) throws IOException, XmlPullParserException;
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    public Model read(InputStream in, boolean strict, String encoding, InputSource source) throws IOException, XmlPullParserException;
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}
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```
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**Usage Example:**
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```java
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import org.apache.maven.model.Model;
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import org.apache.maven.model.InputLocation;
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import org.apache.maven.model.io.xpp3.MavenXpp3ReaderEx;
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MavenXpp3ReaderEx readerEx = new MavenXpp3ReaderEx();
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try {
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    Model model = readerEx.read(new FileReader("pom.xml"), true);
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    // Access location information for error reporting
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    InputLocation location = model.getLocation("version");
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    if (location != null) {
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        System.out.println("Version defined at line: " + location.getLineNumber());
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    }
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} catch (Exception e) {
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    System.err.println("Parse error: " + e.getMessage());
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}
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```
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### MavenXpp3Writer
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Standard XML writer for serializing Model objects to POM XML format.
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```java { .api }
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public class MavenXpp3Writer {
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    // Basic writing methods
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    public void write(Writer writer, Model model) throws IOException;
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    public void write(OutputStream stream, Model model) throws IOException;
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    // Methods with encoding control
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    public void write(Writer writer, Model model, String encoding) throws IOException;
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    public void write(OutputStream stream, Model model, String encoding) throws IOException;
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}
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```
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**Usage Example:**
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```java
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import org.apache.maven.model.Model;
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import org.apache.maven.model.io.xpp3.MavenXpp3Writer;
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import java.io.FileWriter;
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import java.io.IOException;
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// Create or modify model
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Model model = new Model();
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model.setModelVersion("4.0.0");
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model.setGroupId("com.example");
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model.setArtifactId("my-project");
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model.setVersion("1.0.0");
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MavenXpp3Writer writer = new MavenXpp3Writer();
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try {
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    // Write to file
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    writer.write(new FileWriter("output-pom.xml"), model);
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    // Write to file with specific encoding
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    writer.write(new FileWriter("utf8-pom.xml"), model, "UTF-8");
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    System.out.println("POM file written successfully");
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} catch (IOException e) {
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    System.err.println("Error writing POM: " + e.getMessage());
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}
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```
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### MavenXpp3WriterEx
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Extended XML writer with advanced formatting options and comment preservation.
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```java { .api }
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public class MavenXpp3WriterEx {
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    // Writing methods with extended formatting
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    public void write(Writer writer, Model model) throws IOException;
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    public void write(OutputStream stream, Model model) throws IOException;
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    // Methods with encoding and formatting control
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    public void write(Writer writer, Model model, String encoding) throws IOException;
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    public void write(OutputStream stream, Model model, String encoding) throws IOException;
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}
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```
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**Key Features:**
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- **Location Tracking**: Extended reader tracks source locations for each model element
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- **Error Reporting**: Precise line/column information for validation errors
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- **Comment Preservation**: Extended writer can preserve XML comments and formatting
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- **Encoding Support**: Full UTF-8 and other encoding support
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- **Strict vs Lenient**: Option to ignore unknown XML elements for forward compatibility
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### Error Handling
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All I/O operations can throw these exceptions:
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```java
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// XML parsing errors
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catch (XmlPullParserException e) {
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    System.err.println("XML syntax error: " + e.getMessage());
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    System.err.println("Line: " + e.getLineNumber() + ", Column: " + e.getColumnNumber());
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}
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// File I/O errors  
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catch (IOException e) {
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    System.err.println("File I/O error: " + e.getMessage());
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}
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```
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### InputSource and InputLocation
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Used by extended readers for tracking source information:
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```java { .api }
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public class InputSource {
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    public String getLocation();
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    public String getModelId();
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}
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public class InputLocation {
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    public int getLineNumber();
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    public int getColumnNumber();
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    public InputSource getSource();
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    public Map<Object, InputLocation> getLocations();
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}
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```
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**Usage for IDE Integration:**
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```java
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// Create input source for tracking
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InputSource source = new InputSource();
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source.setLocation("pom.xml");
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source.setModelId("com.example:my-project:1.0.0");
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// Read with source tracking
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Model model = readerEx.read(new FileReader("pom.xml"), true, source);
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// Later, get location of any element for error reporting or IDE navigation
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InputLocation versionLoc = model.getLocation("version");
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if (versionLoc != null) {
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    int line = versionLoc.getLineNumber();
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    int column = versionLoc.getColumnNumber();
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    String file = versionLoc.getSource().getLocation();
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    // Use for IDE "Go to Definition" or error highlighting
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}
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```