Spring-MongoDB 关键类的源码分析

本文分析的是 spring-data-mongodb-1.9.2.RELEASE.jar 和 mongodb-driver-core-3.2.2.jar。

一、UML Class Diagram

核心类是 MongoTemplate，下面这张 UML 类图涉及了主要的类，省略了次要的类。

涉及的类： MongoTemplate,

MongoOperations,

MongoDbFactory,

SimpleMongoDbFactory,

Mongo,

MongoClient,

MongoCredential,

ServerAddress。

二、源码分析

 （1） MongoTemplate

MongoTemplate 是 Spring-MongoDB 整合的核心类，它实现了 MongoOperations 接口（该接口定义了 CRUD 操作）。

MongoTemplate 有个核心的构造方法（其他重载的构造方法最终都会调用这个构造方法）：

    /**
     * Constructor used for a basic template configuration.
     * 
     * @param mongoDbFactory must not be {@literal null}.
     * @param mongoConverter
     */
    public MongoTemplate(MongoDbFactory mongoDbFactory, MongoConverter mongoConverter) {

        Assert.notNull(mongoDbFactory);

        this.mongoDbFactory = mongoDbFactory;
        this.exceptionTranslator = mongoDbFactory.getExceptionTranslator();
        this.mongoConverter = mongoConverter == null ? getDefaultMongoConverter(mongoDbFactory) : mongoConverter;
        this.queryMapper = new QueryMapper(this.mongoConverter);
        this.updateMapper = new UpdateMapper(this.mongoConverter);

        // We always have a mapping context in the converter, whether it's a simple one or not
        mappingContext = this.mongoConverter.getMappingContext();
        // We create indexes based on mapping events
        if (null != mappingContext && mappingContext instanceof MongoMappingContext) {
            indexCreator = new MongoPersistentEntityIndexCreator((MongoMappingContext) mappingContext, mongoDbFactory);
            eventPublisher = new MongoMappingEventPublisher(indexCreator);
            if (mappingContext instanceof ApplicationEventPublisherAware) {
                ((ApplicationEventPublisherAware) mappingContext).setApplicationEventPublisher(eventPublisher);
            }
        }
    }

可以看到，这个构造方法至少需要一个参数 mongoDbFactory，MongoTemplate 类中其他字段都可以内部构造出来。

（2）MongoDbFactory

MongoDbFactory 是一个接口，用于新建 DB 实例。

它的实现之一是 SimpleMongoDbFactory。

public interface MongoDbFactory {

    /**
     * Creates a default {@link DB} instance.
     * 
     * @return
     * @throws DataAccessException
     */
    DB getDb() throws DataAccessException;

    /**
     * Creates a {@link DB} instance to access the database with the given name.
     * 
     * @param dbName must not be {@literal null} or empty.
     * @return
     * @throws DataAccessException
     */
    DB getDb(String dbName) throws DataAccessException;

    /**
     * Exposes a shared {@link MongoExceptionTranslator}.
     * 
     * @return will never be {@literal null}.
     */
    PersistenceExceptionTranslator getExceptionTranslator();
}

（3） SimpleMongoDbFactory

SimpleMongoDbFactory 实现了 MongoDbFactory 接口（以下省略了部分代码）：

public class SimpleMongoDbFactory implements DisposableBean, MongoDbFactory {

    private final Mongo mongo;
    private final String databaseName;
    private final boolean mongoInstanceCreated;
    private final UserCredentials credentials;
    private final PersistenceExceptionTranslator exceptionTranslator;
    private final String authenticationDatabaseName;

    private WriteConcern writeConcern;
    
    /**
     * Creates a new {@link SimpleMongoDbFactory} instance from the given {@link MongoClientURI}.
     * 
     * @param uri must not be {@literal null}.
     * @throws UnknownHostException
     * @since 1.7
     */
    public SimpleMongoDbFactory(MongoClientURI uri) throws UnknownHostException {
        this(new MongoClient(uri), uri.getDatabase(), true);
    }

    /**
     * Creates a new {@link SimpleMongoDbFactory} instance from the given {@link MongoClient}.
     * 
     * @param mongoClient must not be {@literal null}.
     * @param databaseName must not be {@literal null}.
     * @since 1.7
     */
    public SimpleMongoDbFactory(MongoClient mongoClient, String databaseName) {
        this(mongoClient, databaseName, false);
    }

    private SimpleMongoDbFactory(Mongo mongo, String databaseName, UserCredentials credentials,
            boolean mongoInstanceCreated, String authenticationDatabaseName) {

        if (mongo instanceof MongoClient && (credentials != null && !UserCredentials.NO_CREDENTIALS.equals(credentials))) {
            throw new InvalidDataAccessApiUsageException(
                    "Usage of 'UserCredentials' with 'MongoClient' is no longer supported. Please use 'MongoCredential' for 'MongoClient' or just 'Mongo'.");
        }

        Assert.notNull(mongo, "Mongo must not be null");
        Assert.hasText(databaseName, "Database name must not be empty");
        Assert.isTrue(databaseName.matches("[\w-]+"),
                "Database name must only contain letters, numbers, underscores and dashes!");

        this.mongo = mongo;
        this.databaseName = databaseName;
        this.mongoInstanceCreated = mongoInstanceCreated;
        this.credentials = credentials == null ? UserCredentials.NO_CREDENTIALS : credentials;
        this.exceptionTranslator = new MongoExceptionTranslator();
        this.authenticationDatabaseName = StringUtils.hasText(authenticationDatabaseName) ? authenticationDatabaseName
                : databaseName;

        Assert.isTrue(this.authenticationDatabaseName.matches("[\w-]+"),
                "Authentication database name must only contain letters, numbers, underscores and dashes!");
    }

    /**
     * @param client
     * @param databaseName
     * @param mongoInstanceCreated
     * @since 1.7
     */
    private SimpleMongoDbFactory(MongoClient client, String databaseName, boolean mongoInstanceCreated) {

        Assert.notNull(client, "MongoClient must not be null!");
        Assert.hasText(databaseName, "Database name must not be empty!");

        this.mongo = client;
        this.databaseName = databaseName;
        this.mongoInstanceCreated = mongoInstanceCreated;
        this.exceptionTranslator = new MongoExceptionTranslator();
        this.credentials = UserCredentials.NO_CREDENTIALS;
        this.authenticationDatabaseName = databaseName;
    }

}

核心构造方法：

/**
     * @param client
     * @param databaseName
     * @param mongoInstanceCreated
     * @since 1.7
     */
    private SimpleMongoDbFactory(MongoClient client, String databaseName, boolean mongoInstanceCreated) {

        Assert.notNull(client, "MongoClient must not be null!");
        Assert.hasText(databaseName, "Database name must not be empty!");

        this.mongo = client;
        this.databaseName = databaseName;
        this.mongoInstanceCreated = mongoInstanceCreated;
        this.exceptionTranslator = new MongoExceptionTranslator();
        this.credentials = UserCredentials.NO_CREDENTIALS;
        this.authenticationDatabaseName = databaseName;
    }

第一个参数 MongoClient client（MongoClient）: 包含 host, port, username, password 等信息。

（4）MongoClient 与 Mongo

MongoClient 继承了 Mongo。

/**
     * Creates a Mongo instance based on a (single) mongo node using a given ServerAddress and default options.
     *
     * @param addr            the database address
     * @param credentialsList the list of credentials used to authenticate all connections
     * @param options         default options
     * @see com.mongodb.ServerAddress
     * @since 2.11.0
     */
    public MongoClient(final ServerAddress addr, final List<MongoCredential> credentialsList, final MongoClientOptions options) {
        super(addr, credentialsList, options);
    }

这个核心构造方法接收三个参数：

final ServerAddress addr：可以由 new ServerAddress(host, port) 构造。

final List<MongoCredential> credentialsList： 包含 username, password 等信息。

final MongoClientOptions options： 包含 MongoDB 数据库的配置信息。

（5） MongoCredential

MongoCredential 包含 username, password 等信息。

public final class MongoCredential {

    private final AuthenticationMechanism mechanism;
    private final String userName;
    private final String source;
    private final char[] password;
    private final Map<String, Object> mechanismProperties;
    
    // Other code
}

三、其他

Spring-MongoDB 整合与 Spring-MyBatis 相似。

Spring-MyBatis 的核心类是 SqlSessionTemplate，作用与 MongoTemplate 一样。